27
Fields of Application / Industry: Chemistry / Polymer Industry Clinical Chemistry / Medicine / Hygiene/ Health Care Electronics Semi-Conductor Technology Energy Environment / Water / Waste Geology / Mining Food / Agriculture Metallurgy / Galvanization Refineries / Petrochemistry Pharmacy Cosmetics Material Analysis Others

Sample Preparation for Metals in Food

Embed Size (px)

DESCRIPTION

sample prep

Citation preview

  • Fields of Application / Industry:

    Chemistry / Polymer Industry Clinical Chemistry / Medicine /

    Hygiene/ Health Care

    Electronics Semi-Conductor Technology Energy Environment / Water / Waste Geology / Mining Food / Agriculture Metallurgy / Galvanization Refineries / Petrochemistry Pharmacy Cosmetics Material Analysis Others

  • Dow

    nloa

    ded

    By:

    [Kor

    n, M

    aria

    das

    Gra

    as

    And

    rade

    ] At:

    13:3

    0 6

    Febr

    uary

    200

    8

    Sample Preparation for the Determinationof Metals in Food Samples Using

    Spectroanalytical MethodsA Review

    Maria das Gracas Andrade Korn,1 Elane Santos da BoaMorte,1 Daniele Cristina Muniz Batista dos Santos,1

    Jacira Teixeira Castro,1 Jose Tiago Pereira Barbosa,1

    Alete Paixao Teixeira,1 Andrea Pires Fernandes,1

    Bernhard Welz,1 Wagna Piler Carvalho dos Santos,1,2

    Eduardo Batista Guimaraes Nunes dos Santos,3

    and Mauro Korn3

    1NQA/GPQA, Instituto de Qumica, Universidade Federal da Bahia,Campus de Ondina, Salvador, Bahia, Brazil

    2Centro Federal de Educacao Tecnologica da Bahia, Barbalho,

    Salvador-Bahia, Brazil3NQA/SONOFIA, Departamento de Ciencias Exatas e da Terra,

    Universidade do Estado da Bahia, Salvador, BA, Brazil

    Abstract: The present article gives an overview of recent publications and modern

    techniques of sample preparation for food analysis employing atomic and inorganic

    mass spectrometric techniques, such as flame atomic absorption spectrometry,

    chemical vapor generation atomic absorption and atomic fluorescence spectrometry,

    graphite furnace atomic absorption spectrometry, inductively coupled plasma optical

    emission spectrometry, and inductively coupled plasma mass spectrometry. Among

    the most frequently applied sample preparation techniques for food analysis are dry

    ashing, usually with the addition of an ashing aid, and acid digestion, preferably

    with the assistance of microwave energy. Slurry preparation, particularly with the

    assistance of ultrasound, is increasingly used to reduce acid consumption and sample

    preparation time. Direct analysis of solid samples is gaining importance in the field

    of food analysis as it offers the highest sensitivity, avoids the use of acids and other

    Address correspondence to Maria das Gracas Andrade Korn, NQA/GPQA,Instituto de Qumica, Universidade Federal da Bahia, Campus de Ondina, 40170-115

    Salvador, Bahia, Brazil. E-mail: [email protected]

    Applied Spectroscopy Reviews, 43: 6792, 2008

    Copyright# Taylor & Francis Group, LLCISSN 0570-4928 print/1520-569X onlineDOI: 10.1080/05704920701723980

    67

  • Dow

    nloa

    ded

    By:

    [Kor

    n, M

    aria

    das

    Gra

    as

    And

    rade

    ] At:

    13:3

    0 6

    Febr

    uary

    200

    8

    aggressive reagents, makes possible the analysis of micro-samples, and can be applied

    for fast screening analysis, e.g., of fresh meat.

    Keywords: Food samples, sample preparation, trace element determination, atomic

    spectrometry, inorganic mass spectrometry

    INTRODUCTION

    Elemental food composition data are important to both consumers and health

    professionals, and recent food labeling legislation has highlighted this require-

    ment. The determination of trace elements and contaminants in complex

    matrices, such as food, often requires extensive sample preparation and/orextraction regimes prior to instrumental analysis. Flame atomic absorption

    spectrometry (FAAS), graphite furnace atomic absorption spectrometry (GF

    AAS), and inductively coupled plasma optical emission spectrometry (ICP

    OES) are the main techniques used for the determination of trace element

    contents in food analysis laboratories. The traditional techniques for sample

    preparation are time consuming and require large amounts of reagents,

    which are expensive, generate hazardous waste, and might contaminate the

    sample with the analytes. Advances in sample preparation over the last few

    decades have been propelled by the advance of microwave-assisted acid

    digestion (13), ultrasound-assisted, extraction and slurry preparation (4),

    and direct solid sampling analysis (5).

    Quality control and safety in the food supply chain demands reliable

    methodology that is both rapid and easily transferable. In order to minimize

    the uncertainty in sample preparation a number of factors need to be con-

    sidered. As statistically the degree of uncertainty in a method is directly

    related to the number of stages involved, a minimization of that number

    should reduce the uncertainty proportionally. Automation and mechanization

    of processes also leads to a reduction in uncertainty. Automated procedures

    are generally more reproducible than manual methods and will also

    decrease the staff time spent on sample preparation, which is often the bottle-

    neck in analytical laboratories (4, 5).

    This review will discuss recent development in procedures for sample

    preparation of food samples particularly under the above-mentioned aspects.

    The discussion emphasizes analytes, samples, and effects on measurement

    conditions using atomic and mass spectrometric techniques.

    DRY-ASHING TECHNIQUES

    Dry ashing is a sample preparation method generally convenient to be applied

    for subsequent trace metal determination in food materials. Dry ashing or

    oxidation is usually performed by placing 0.11 g of the sample in an open

    M. das G. A. Korn et al.68

  • Dow

    nloa

    ded

    By:

    [Kor

    n, M

    aria

    das

    Gra

    as

    And

    rade

    ] At:

    13:3

    0 6

    Febr

    uary

    200

    8

    vessel and removing the organic matter from the samples by thermal

    decomposition, normally in the presence of an ashing aid, using a muffle

    furnace. Typical ashing temperatures are 450 to 5508C at atmosphericpressure, and the ash residues are dissolved in an appropriate acid. The

    degree of volatilization loss is a limiting factor and depends on (i) the

    applied temperature, (ii) the form in which the analyte is present in the

    sample, and (iii) the chemical environment in the ashing stage. Oxidizing

    reagents may be used as ashing aids in order to prevent the volatilization of

    analytes and also to speed up the ashing process. High-purity magnesium

    nitrate and magnesium oxide are commonly used for that purpose (6).

    Several papers have been published about dry ashing as a sample prep-

    aration method for metal determination in food samples. Tuzen et al. investi-

    gated the application of dry ashing to promote the decomposition of fish (7),

    baby food (8), and honey (9). Approximately 1 g of sample was submitted to

    dry ashing at 4508C for 416 h, depending on the matrix, and the residue wasdissolved in nitric acid. Aluminum, Cd, Co, Cr, Cu, Fe, Mn, Se, and Zn were

    determined using GF AAS; recoveries were quantitative (95%) for all inves-tigated elements.

    Mindak et al. (10) developed a flow-injection hydride generation atomic

    absorption spectrometry (FI-HG AAS) method for the determination of total

    arsenic and selenium in food. A combination of microwave-assisted

    digestion with nitric acid and dry ashing utilizing magnesium nitrate and

    magnesium oxide as ashing aids was used to destroy the organic matrix

    including refractory organometallic compounds present in many food

    samples. Complete mineralization of these compounds is a pre-requirement

    for the application of hydride generation for these elements. The resulting

    ash was dissolved in hydrochloric acid and diluted to volume. The method

    was validated using 21 food samples and nine reference materials.

    The application of dry ashing methods is simple and large quantities of

    food samples may be treated at the same time. This procedure permits the pre-

    concentration of trace elements in the final solution, which is useful when very

    low concentrations are to be determined. The ash is also completely free of

    organic matter, which is a prerequisite for some analytical techniques. The

    addition of an ashing aid, on the other hand, increases the content of

    inorganic salts significantly, which might be a problem for the subsequent

    determination of trace elements, and it might also contribute to contamination,

    necessitating careful blank control.

    WET-ASHING TECHNIQUES

    Wet digestion methods include sample decomposition by an acid or mixtures

    of acids, carried out in open vessels, in tubes, on a hot plate or in an aluminum

    heating block or in closed vessels at elevated pressure (digestion bombs) with

    thermal or microwave heating. Microwave-assisted digestion is an attractive

    Determination of Metals in Foods 69

  • Dow

    nloa

    ded

    By:

    [Kor

    n, M

    aria

    das

    Gra

    as

    And

    rade

    ] At:

    13:3

    0 6

    Febr

    uary

    200

    8

    method, especially for small samples. Extreme care should be exercised in

    using sealed pressure vessels since there is much anecdotal evidence of

    these vessels rupturing occasionally during conventional or microwave-

    assisted digestion of organic materials. The applicability of this technique is

    strictly dependent on the type of food: carbohydrates are easily mineralized

    with nitric acid at 1808C, while fats, proteins, and amino acids cause incom-plete digestion due to the relatively low oxidation potential of nitric acid at

    2008C; these materials require the addition of sulfuric and/or perchloricacid with all the problems related to their use at high temperature and pressure.

    The type of acid used in the preparation procedure can have important

    consequences in the measurement step. It is commonly known that in all

    atomic spectrometric techniques nitric acid is the most desirable reagent. In

    spite of occasionally observed signal suppression in its presence (e.g., in

    ICP OES), no severe analytical problems are encountered in practice with

    nitric acid at concentrations up to 10%, sometimes higher, in all atomic spec-

    trometric techniques as long as its concentration is similar in calibration and

    sample solutions. Hydrogen peroxide, added in most mineralization pro-

    cedures, is also rarely responsible for analytical problems (1). The presence

    of hydrochloric acid is not troublesome in ICP OES analysis; however, its

    exclusive use is kind of prohibited in GF AAS analysis because of the

    possible formation of volatile and difficult-to-dissociate analyte chlorides

    that could cause vapor phase and/or spectral interference (11). Because ofits high viscosity, utilization of sulfuric acid is usually avoided in spite of

    its efficiency in digestion of organic matrices. Its presence is particularly unde-

    sirable in analytical techniques where the sample introduction is by nebuliza-

    tion (FAAS, ICP OES, ICP-MS).

    Momen et al. (12) investigated two digestion procedures for the determi-

    nation of essential (Cr, Cu, Fe, Mg, Mn, Zn) and non-essential (Al, Ba, Cd, Pb)

    elements in nuts by ICP OES. The procedures included wet digestion with

    HNO3/H2SO4 and HNO3/H2SO4/H2O2 in PTFE vessels and experimentaldesigns were used for optimization. The factors studies were HNO3, H2SO4,

    and H2O2 volumes, digestion time, predigestion time, temperature of the hot

    plate, and sample weight. The factors HNO3 and H2O2 volume and the

    digestion time were found to be the most important parameters. The good

    agreement between measured and certified values for all analytes (relative

    error , 11%) in two certified reference materials (CRM), IAEA-331,spinach leaves and IAEA-359, cabbage, indicates that the developed analyti-

    cal method was working well.

    In another study, Momen et al. (13) assessed four procedures for the deter-

    mination of essential (Cr, Cu, Fe, Mg, Mn, Zn) and toxic (Al, Cd, Pb) elements

    in legumes by ICP OES. These included wet digestion with HNO3/H2SO4 andHNO3/H2SO4/H2O2 and dry ashing with Mg(NO3)2 and Mg(NO3)2/HNO3,respectively. The precision, expressed as RSD for an aqueous standard con-

    taining 250 mg L21 of each analyte, was in the range of 1.58.0%. Theaccuracy, expressed as relative error was generally within the range of

    M. das G. A. Korn et al.70

  • Dow

    nloa

    ded

    By:

    [Kor

    n, M

    aria

    das

    Gra

    as

    And

    rade

    ] At:

    13:3

    0 6

    Febr

    uary

    200

    8

    0.510% for all analytes, and the quantification limits were lower than

    2.5 mg g21. Although acceptable results were obtained with all procedures,wet digestion with HNO3/H2SO4/H2O2 was recommended because of thebetter recovery. The good agreement between measured and certified concen-

    trations for IAEA-331 and IAEA-359 CRM indicates that the developed

    analytical method is well suited for the determination of toxic and nutrient

    elements in legumes and possibly similar matrices.

    ICP OES with continuous hydride generation was used for the determi-

    nation of As in seafood samples (14). The lyophilized samples were

    digested with concentrated nitric and sulfuric acid. The reliability of the

    developed method was checked by analyzing several CRM. Complete miner-

    alization was obtained for an arsenobetaine-containing CRMwith a mixture of

    nitric and sulfuric acids followed by adding hydrogen peroxide in an open

    digestion system and a digestion time of 4 h.

    Studies on the transfer of chemical contaminants through the food chain

    provide useful information for the development of surveillance programs

    aimed at ensuring the safety of the food supply and minimizing human

    exposure to toxic agents. Tinggi et al. (15) investigated two wet digestion pro-

    cedures using acid mixtures of HNO3/H2SO4/HClO4 and HNO3/H2SO4 fordecomposition of food samples in Australian diet. The addition of hydrofluo-

    ric acid to the mixture of HNO3/HSO4 was also investigated for the determi-nation of Cr. All the acid mixtures tested were found to be satisfactory but, for

    safety reasons, HNO3/H2SO4 was the method of choice. Olivares et al. (16)employed a wet digestion procedure using a mixture of nitric, perchloric,

    and sulfuric acids for sample preparation of common Chilean foods for the

    determination of Fe, Zn, and Cu by FAAS and assessed the intake of these

    elements in a population living in Santiago, Chile. In another study, the

    levels of essential elements, such as Cu, Cr, Fe, and Zn, and toxic elements

    such as Al, Ni, Pb, and Cd were evaluated in a total of 40 samples of

    legumes and 56 samples of nuts that are widely consumed in Spain (17).

    These samples were mineralized in a digestion block with HNO3 and V2O5and determined using GF AAS as the analytical technique. The reliability of

    the procedure was checked by the analysis of a CRM; no matrix effects

    were observed and aqueous standard solutions were used for calibration.

    Kira et al. (18) developed a fast procedure for the determination of Ca, Cr,

    Cu, Fe, K, Mg, Mn, Na, P, and Zn in milk samples by ICP OES. This procedure

    consisted of a partial digestion with hydrochloric acid on a hot plate. The results

    were compared with two digestion procedures (dry ashing and microwave-

    assisted acid digestion). All the procedures showed similar levels of

    precision, with coefficients of variation ,10% for the majority of theelements. The accuracy was evaluated using a CRM, and the values were

    within the confidence intervals for these products. Rodriguez et al. (19) used

    a mixture of HNO3 and HClO4 (9:1 v/v) for the preparation of bovine milksamples. Calcium, Cu, Fe, K, Mg, Na, Se, and Zn were determined by

    FAAS, FAES, and fluorimetry. In another paper, Cava-Montesinos et al. (20)

    Determination of Metals in Foods 71

  • Dow

    nloa

    ded

    By:

    [Kor

    n, M

    aria

    das

    Gra

    as

    And

    rade

    ] At:

    13:3

    0 6

    Febr

    uary

    200

    8

    compared two sample preparation procedures for bovine milk samples for the

    determination of Se and Te by HG AFS. The first digestion was in a

    microwave oven using HNO3 and 30% v/v H2O2. The other procedureconsisted of many stages using a muffle furnace and a hot plate. A suspension

    with 10% (m/v) Mg(NO3)2 . 6H2O and 1% (m/v), MgO as an ashing aid wasused for dry ashing of the sample in the muffle furnace. The ash was treated with

    KBr and HCl before the quantification of the analytes using HG AFS. The

    proposed method involved the use of a low-cost instrumentation, and

    microwave-assisted sample pretreatment provides fast and accurate results.

    Ferreira et al. (21) developed an acid digestion procedure for the determi-

    nation of Cu in various food samples of animal and plant origin. A (3:1 v/v)mixture of HNO3:HClO4 was used for digestion of the samples on a hot plate

    until the total oxidation of the organic material. Copper was determined by

    FAAS.

    Santos et al. (22) proposed a fast and inexpensive wet digestion procedure

    for beans samples. Essential (Ca, Cu, Fe, K, Mg, Mn, Ni, P, Zn) and non-

    essential (Al, Ba, Sr) elements were determined in bean digestates by ICP

    OES. Experimental designs for five factors (HNO3 and H2O2 volume,

    digestion time, block temperature, and particle size) were used for optimiz-

    ation of the digestion procedure, adopting a factorial experiment with 2521

    design. The factor block temperature was found to be the most important

    parameter and Doehlert designs were applied in order to determine the

    optimum conditions. Digestion conditions were attained using 3.5 mL of con-

    centrated HNO3 for 45 min. The accuracy of the results was demonstrated

    using one CRM (spinach leaves NIST 1570a) and comparison with the

    recommended official method.

    Microwave-Assisted Digestion

    Microwave (MW)-assisted digestion with nitric acid, nitric and hydrochloric

    acids without or with the addition of hydrogen peroxide is a widely used

    technique for the dissolution of food samples. Microwave heating has

    several advantages over conventional heating on a hot plate, etc., as the

    energy is generated in the digestion mixture and not transferred by conduction.

    Among the key advantages of MW-assisted digestion are the much shorter

    digestion times and the reduced need for aggressive reagents to obtain

    complete digestion. There are two different systems available for MW-

    assisted digestion, pressurized closed-vessel systems and open focused-MW

    systems that work under atmospheric pressure. Microwave-assisted

    digestion in closed vessels under pressure has gained popularity as a simple

    and fast dissolution technique that minimizes acid consumption, the risk of

    sample contamination, and loss of volatile elements. One of the limitations

    is the time required for cooling before the vessels can be opened, which

    may take hours, depending on the type of equipment used. The main

    M. das G. A. Korn et al.72

  • Dow

    nloa

    ded

    By:

    [Kor

    n, M

    aria

    das

    Gra

    as

    And

    rade

    ] At:

    13:3

    0 6

    Febr

    uary

    200

    8

    advantages of focused-MW radiation are safety, versatility, control of

    microwave energy released to the sample, and the possibility for programmed

    addition of solutions during the digestion. However, loss of volatile elements

    cannot be excluded in open-vessel digestion and results for low-level elements

    might be affected by the high amount of reagents used and hence the increased

    risk of sample contamination. This risk can be minimized by using vapor-

    phase acid digestion, which has proven to be very effective in minimizing

    the residual carbon content (RCC) (1, 2).

    Table 1 gives an overview of more recent applications of MW-assisted

    digestion for the analysis of food samples. Doner and Ege (23) evaluated

    Table 1. Microwave-assisted dissolution for diverse food samples

    Food Reagents Analytes Technique Ref.

    Biscuits HNO3, HCl Fe, Zn FAAS (23)

    Bread and

    biscuits

    HNO3, H2O2 Al GF AAS (24)

    Beans HNO3, H2SO4 Ca, Fe, Mg, Mn, Zn ICP OES (25)

    Flour HNO3, H2O2 Fe, Mn, Zn FAAS (26)

    Herbal tea HNO3, H2O2 Mg, Al, Ca, V, Cr,

    Mn, Fe, Co, Ni, Cu,

    Zn, Se, Sr, Sb, Ba,

    As, Cd, Hg, Pb

    ICP-MS (27)

    Tea HNO3 Al, Ca, Mg, Mn ICP OES (28)

    Wheat grain HNO3, H2O2 Cd, Cr, Fe, Ni, Pb ICP OES, ICP-MS (29)

    Durum wheat

    flour

    HNO3, H2O2 Cd, Cr, Fe, Ni, Pb ICP OES, ICP-MS (30)

    Edible oil HNO3, H2O2 Al, Ca, Co, Cr, Cu,

    Fe, K, Mg, Mn, Na,

    Ni, Pb, Zn

    ICP OES, GF AAS (31)

    Olive oil HNO3, H2O2 Al, Ca, Co, Cr, Cu,

    Fe, K, Mg, Mn, Na,

    Ni, Pb, Zn

    ICP OES, GF AAS (32)

    Bovine milk HNO3, H2SO4 Ba, Ca, Cu, K, Mg,

    Na, P, Zn

    ICP OES (33)

    Milk powder HNO3, H2O2, TiO2 Al, Ca, Cu, Fe, Mg,

    Na, Se, Zn

    ICP OES, GF AAS (34)

    Yogurt HNO3, H2O2 Al, Fe, and Zn FAAS (35)

    Bovine liver HNO3, H2SO4NaClO4, H2O2

    Al, Ca, Cu, Fe, Mg,

    Mn, Zn

    ICP OES (36)

    Fish HNO3 Cd, Cu, Ni, Pb, Zn GF AAS (38)

    Fish Hg CV AFS (39)

    Fish TMAH As GF AAS (40)

    Milk powder NH4NO3 Cu, Zn FAAS (41)

    Vegetables HNO3, H2O2 Ba, Ca, Cu, K, Mg,

    Mn, P, S, Zn,

    ICP OES (42)

    Determination of Metals in Foods 73

  • Dow

    nloa

    ded

    By:

    [Kor

    n, M

    aria

    das

    Gra

    as

    And

    rade

    ] At:

    13:3

    0 6

    Febr

    uary

    200

    8

    different digestion methods for biscuits prior to the determination of iron and

    zinc using FAAS. In an initial study, MW-assisted digestion with hydrochloric

    and nitric acids 3:1 v/v, 1808C, and 600 W provided an accuracy (spikerecovery 96102%), precision and digestion time comparable to dry ashing,

    wet digestion (using different acid mixtures), and also to a simple acid

    treatment at room temperature. The latter technique was further investigated

    because of its simplicity and to reduce the digestion time. The addition of

    ethanol was found necessary to digest the organic residue at room tempera-

    ture. The method was validated by comparison of the data found for commer-

    cial biscuit samples using the proposed procedure and the AOAC official

    spectrophotometric reference method. Jalbani et al. (24) investigated the

    dietary intake of aluminum in bakery products consumed in the urban areas

    of Hyderabad, Pakistan. Samples of different branded and non-branded

    bread and biscuits were dissolved using MW-assisted and conventional wet

    acid digestion prior to GF AAS analysis.

    Costa et al. (25) used a factorial design for optimization of a focused-

    MWassisted digestion of bean samples for the determination of Ca, Fe,

    Mg, Mn, and Zn. A closed-vessel MW-assisted digestion was used to

    certify the elemental compositions obtained after open digestion. The

    accuracy was checked using the NIST SRM 8433 Corn Bran CRM. Results

    were in agreement with certified values at the 95% confidence limit using a

    Students t-test. Volumes of nitric and sulfuric acid, temperature, and the

    interaction between the initial volumes of HNO3 and H2SO4 were significant

    variables according to the P-values in the analysis of variance (ANOVA).

    Santelli et al. (26) also used a Doehlert matrix response surface method to

    optimize a focused-MWassisted digestion of various food samples for the

    determination of Fe, Mn, and Zn by FAAS. Three variables, irradiation

    power, irradiation time, and composition of the oxidant solution

    (HNO3H2O2), were considered as factors in the optimization study. Theworking conditions were established as a compromise between optimum

    values found for each analyte, taking into consideration the robustness of

    the procedure. These values were 260 W, 12 min, and 42% (v/v) forirradiation power, irradiation time, and percentage of H2O2 in solution,

    respectively. The accuracy of the optimized procedure was evaluated by the

    analysis of CRM and by comparison with a well-established closed-vessel

    MW-assisted digestion method.

    Nookabkaew et al. (27) used MW-assisted digestion for three types of

    popular herbal tea products, Gynostemma pentaphyllum, Camellia sinensis,

    and Morus alba, which are widely consumed in Thailand and in the rest of

    the world. The contents of Mg, Al, Ca, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Se,

    Sr, Sb, Ba, As, Cd, Hg, and Pb were determined by ICP-MS. Costa et al.

    (28) investigated a focused-MWassisted extraction of Al, Ca, Mg, and Mn

    in tea leaves. The efficiency of extraction was evaluated using diluted acid

    and alkaline solution of a tertiary amine in water. The extraction procedure

    was implemented in 5 min. A hot plate digestion procedure was developed

    M. das G. A. Korn et al.74

  • Dow

    nloa

    ded

    By:

    [Kor

    n, M

    aria

    das

    Gra

    as

    And

    rade

    ] At:

    13:3

    0 6

    Febr

    uary

    200

    8

    for comparison. A colorless digest was obtained for all the tea samples and the

    total content for each analyte was used to calculate the efficiency of the extrac-

    tion. The determination was carried out by FAAS and ICP OES; quantitative

    recovery (80100%) was obtained for Ca, Mg, and Mn, but for Al recoveries

    were only 1080%, which is probably due to the strong interaction of this

    element with the matrix. The results indicated that the percentages of extrac-

    tion of the elements are directly related with the chemical form in which the

    metal is present in the tea leaf.

    Cubadda et al. (29, 30) used closed-vessel MW-assisted digestion for

    determination of Cd, Pb, Fe, Ni, and Cr in selected food matrices by plasma

    spectrometric techniques and to investigate the transfer of metal contaminants

    through the food chain and the effect of food processing. Cadmium, Pb, Fe,

    Ni, and Cr, were accurately determined in durum wheat grain and

    derived products, wheat-based reference materials, and drinking water, used

    both as an ingredient and for technology purposes in the industrial process.

    The analytical determination was performed using ICP-MS. Changes in

    the sample introduction system and complementary use of ICP OES

    overcame the difficulties in determining the analytes in the food matrixes.

    The benefits of ultrasonic nebulization in reducing spectral interferences

    were demonstrated. Overall, a robust analytical method with high sample

    throughput was developed.

    The determination of trace elements in edible oils is important because of

    both the metabolic role of metals and possibilities for adulteration detection

    and oil characterization. Zeiner et al. (31) used an MW-assisted digestion of

    the olive oil in closed vessels with a mixture of nitric acid and hydrogen

    peroxide; the trace element content of olive oils was determined by ICP

    OES and GF AAS. Recently, the quantification of selected metals in various

    oils (olive, pumpkin seed, sunflower, sesame seed, hazelnut, grape, soy, and

    rice oil) was carried out by ICP OES and GF AAS after MW-assisted

    digestion (32). Differences in the metal concentrations for edible oils

    obtained in this preliminary study were the basis for the development of an

    additional analytical procedure applicable for oil characterization.

    Santos et al. (33) developed a method for the determination of Ba, Ca, Cu,

    K, Mg, Na, P, and Zn in whole and non-fat bovine milk after digestion in a

    focused MW oven, using an alternate procedure based on gradual sample

    addition to hot and concentrated acids. A two-level 23 full factorial design

    experiment with eight runs was carried out to evaluate the optimum exper-

    imental conditions for reducing both the RCC and the final acidity of the

    digestates. The best conditions were attained by adding small aliquots of

    milk (ten additions of a volume of 0.5 mL during 5 min) to a digestion

    mixture containing 3.0 mL nitric acid plus 1.0 mL sulfuric acid heated at

    1058C. It was demonstrated that the digestion efficiency of the alternativeprocedure was better than the conventional procedure; i.e., 98% compared

    to 80% for the latter one. The accuracy was checked using two CRM,

    whole and non-fat milk powder. This strategy expands the application of

    Determination of Metals in Foods 75

  • Dow

    nloa

    ded

    By:

    [Kor

    n, M

    aria

    das

    Gra

    as

    And

    rade

    ] At:

    13:3

    0 6

    Febr

    uary

    200

    8

    focused MW-assisted digestions and produces digestates more suitable for

    measurement using instrumental techniques, such as ICP OES. A novel

    MW-assisted high-temperature/high-pressure UV-TiO2 digestion procedurewas developed for the accelerated decomposition of biological samples such

    as milk (34). The technique is based on a closed, pressurized MW digestion

    apparatus. UV irradiation was generated by an immersed electrodeless

    discharge lamp operated by the focused MW field in the single polymer

    vessel. To enhance oxidation efficiency, a photo catalyst, TiO2, was added

    to the MW-heated Teflon bomb. Measures of digestion completeness were

    provided by the RCC and determination of trace and minor elements,

    enabling a comparison of different digestion procedures and sample types.

    Compared with other digestion systems, unusually low RCC of 12% was

    obtained, corresponding to a digestion efficiency of 9899%.

    Yaman et al. (35) compared digestion methods, such as dry and wet

    ashing and MW-assisted digestion for the treatment of yogurt samples prior

    to the determination of essential nutrients by FAAS. Digestion in a

    microwave oven was found to be an excellent technique in comparison with

    dry and wet ashing for the determination of Al and Zn. Iron in this matrix

    was not completely recovered after MW-assisted digestion using the

    examined conditions. Aluminum concentrations in yogurt samples

    fermented in Al containers were found to be significantly higher than in

    plastic containers. Al concentrations of yogurt taken from the bottom of the

    container were found to be higher than those from the center and top of the

    Al containers.

    An acid-vapor partial digestion procedure for bovine liver has been

    proposed by Trevizan et al. (36) using a focused-MW oven and a labora-

    tory-made PTFE support. The support was equipped with three cups of

    approximately 4 mL volume each and the cups were adapted to the glass

    reaction vessel of the MW oven. A mixture containing HNO3 and H2SO4was heated to 1208C to generate the acid vapor. Bovine liver (5090 mg)were directly weighed into the cups followed by addition of a mixture contain-

    ing NaClO4H2O2. Samples were exposed to acid vapor during 1525 minand then diluted with distilled and deionized water to a final mass of 3.0 g.

    Recoveries of Al, Ca, Cu, Fe, Mg, Mn, and Zn were evaluated using an ICP

    OES with axially viewed configuration. The advantages of using this

    strategy are the reduced concentration of acid in the digestate, the possibility

    of using a technical grade acid without any deterioration of analytical blank,

    and the reduction of blank values due to the purification of reagents during

    MW-assisted evaporation. The main attraction of the proposed procedure is

    that all steps can be carried out in one single vessel, which improves the

    capacity for trace analysis.

    The determination of trace elements in seafood is of interest because of

    nutritional and toxicological reasons. Nutritional because trace metals such

    as Ca, Fe, Mg, Zn, Cu, Co, and Al are necessary for maintenance of

    optimum health, and toxicological as metals such as Pb, Cd, As, and Hg are

    M. das G. A. Korn et al.76

  • Dow

    nloa

    ded

    By:

    [Kor

    n, M

    aria

    das

    Gra

    as

    And

    rade

    ] At:

    13:3

    0 6

    Febr

    uary

    200

    8

    detrimental to health. Furthermore, trace elements are an important aspect of

    environmental analysis because mussels are used as bioindicator organisms to

    assess bioavailability of contaminant concentrations in coastal waters (37). An

    MW-assisted digestion procedure was developed for the determination of Cd,

    Cu, Ni, Pb, and Zn in fish samples from seven sampling stations of the Ria de

    Aveiro (Portugal) by GF AAS (38). The accuracy of the analytical method was

    evaluated through the analysis of two CRM (NIST-1577 band IAEA-V10);

    good agreement was obtained between the experimental results and the

    certified values. The authors concluded that the employed MW-assisted

    digestion method could be considered as a fast procedure, since only 2 min

    was required for a complete dissolution of the sample. Liang et al. (39)

    proposed an automatic system, based on the on-line coupling of high-perform-

    ance liquid chromatography separation, post-column MW-assisted digestion,

    and cold vapor atomic fluorescence spectrometric (CV AFS) determination of

    four mercury compounds in seafood samples. Post-column MW-assisted

    digestion in the presence of potassium persulfate (in HCl), was applied in

    the system to improve the conversion efficiency of three organic mercury

    compounds into inorganic mercury. Parameters influencing the on-line

    digestion efficiency and the separation were optimized. Dogfish muscle

    (DORM-2) was analyzed to verify the accuracy of the method and the

    result was in good agreement with the certified value. Serafimovski et al.

    (40) proposed a simple and fast MW-assisted extraction of arsenic species

    from fish tissue in tetramethylammonium hydroxide (TMAH, 0.075% m/v)or in a water-methanol mixture (80 20 v/v) that took only 20 min. TotalAs was measured by GF AAS directly in the TMAH extract with Pd as a

    modifier ensuring thermal stabilization of all extracted arsenic species.

    Mesko et al. (41) proposed an MW-assisted sample combustion in the

    presence of oxygen under pressure using ammonium nitrate as aid for

    ignition. The system was adapted in a microwave oven with closed quartz

    vessels. A quartz piece was used as a sample holder and to protect the cap

    of the quartz vessel from the flame generated in the combustion process.

    The sample was pressed into a pellet and placed on a disc paper in the

    holder and 50 mL of 50% m/v ammonium nitrate solution was added. Theinfluence of the absorption solution (diluted or concentrated nitric acid or

    water) on the recovery of Cu and Zn was evaluated. About 3 s of

    microwave irradiation was necessary to start the combustion. The combustion

    process was evaluated in relation to the influence of sample mass on the

    ignition time, combustion time, and maximum operation pressure. Bovine

    liver, milk powder, and oyster tissue CRM were used to evaluate the

    accuracy of the procedure for determination of copper and zinc. Results

    from the proposed procedure were also compared to those obtained with con-

    ventional digestion procedures, such as wet digestion in open vessels and

    MW-assisted digestion in closed vessels. The advantages of this procedure

    include the complete sample decomposition in shorter time than with other

    procedures and the acid consumption was always lower than 2%. Other

    Determination of Metals in Foods 77

  • Dow

    nloa

    ded

    By:

    [Kor

    n, M

    aria

    das

    Gra

    as

    And

    rade

    ] At:

    13:3

    0 6

    Febr

    uary

    200

    8

    advantages are the low RCC of less than 1.4% without reflux and less than

    0.3% with a reflux step and the possibility of using diluted acid as the

    absorbing solution.

    Araujo et al. (42) investigated the efficiency of MW-assisted acid digestion

    of plants using different concentrations of nitric acid with hydrogen peroxide

    (30% v/v) by measuring the RCC using ICP OES with axial viewing. TwoCRM, spinach leaves (NIST 1570a) and corn bran (NIST 8433), were used

    for evaluating the accuracy attained when 2 mol L21 HNO3 was employed

    for digestion. Under all experimental conditions RCC values were lower than

    13% w/v, and even the highest concentration did not cause any interferencewith element recovery. It has been observed that the high pressure that is

    attained in closed-vessel operation improved the oxidative action of nitric

    acid due to consequent temperature increase, even when this reagent was not

    used at high concentration. The residual acid present in the digestates varied

    from 1.2 to 4.0 mol L21, depending on the initial acid concentration. Hence,

    for plant materials, MW-assisted acid digestion can be carried out under mild

    conditions, which implies that digestates do not need extensive dilution

    before introduction by pneumatic nebulization into an ICP OES. An additional

    advantage is the lower amount of residue generated when working with less

    concentrated acid solutions.

    Ultrasonic Extraction

    Some conjectural approaches keep up the application of ultrasound irradiation

    to assist metallic species extraction from various solid samples, such as

    intense disturbance imposed by acoustic wave propagation, disruptions

    produced by microjets at the collapse of cavitation bubble, as well as the

    products generated by volatile species sonodegradation. The application of

    ultrasound to assist sample preparation points to some singularities that

    align to the feature of expeditious preparation methods and low reagent con-

    sumption. Ultrasound speeds up sample preparation once it diminishes solvent

    gradient concentration in the solid-liquid interface, yields unstable species

    into the irradiated medium, and, sometimes, increases sample surface area

    due to solid erosion.

    Ultrasound has been employed for sample preparation in order to improve

    analytical throughput (43); however, chemical information of samples

    submitted to ultrasonic irradiation can be severely compromised since the

    collapse of cavitation bubble results in a strong local temperature increase

    and free radical production (4), which could provoke analyte loss and gross

    analytical errors. Analyte losses were also observed for spectrometric determi-

    nations contrasting the results obtained for various metals in food samples pre-

    treated with ultrasound devices with other sample preparation techniques and

    certified materials (4448).

    M. das G. A. Korn et al.78

  • Dow

    nloa

    ded

    By:

    [Kor

    n, M

    aria

    das

    Gra

    as

    And

    rade

    ] At:

    13:3

    0 6

    Febr

    uary

    200

    8

    Nascentes et al. (44) proposed a fast and accurate method for the extrac-

    tion of Ca, Mg, Mn, and Zn from vegetables using ultrasonic energy and dilute

    acid. Optimized conditions for the ultrasonic bath were 1 L of water, 258C,and 2% v/v detergent concentration. The best conditions for extractionwere 0.14 mol L21 HNO3, 10 min of sonication time, and a particle size

    ,75 mm. The accuracy of the proposed ultrasound-assisted extractionmethod was assessed by using certified reference materials, as well as wet

    digestion.

    An ultrasound-assisted leaching procedure using diluted mixed acid

    solution was developed for the determination of cadmium, copper, and zinc

    in fish and mussel samples by FAAS (45). The effects of several parameters

    such as nitric acid, hydrochloric acid, and hydrogen peroxide concentration,

    volume of leaching solution, and sonication time were investigated. A 30-min

    sonication, 568C operating temperature and 6 mL of a 1:1:1 mixture of 4 molL21 HNO3, 4 mol L

    21 HCl, and 0.5 mol L21 H2O2 were used for 0.5 g of

    dried sample. The results from the proposed procedure were compared with

    those obtained by microwave-assisted digestion, and the recovery obtained

    with the leaching technique ranged from 92 to 114% for fish and from 88 to

    103% for mussel samples. The accuracy of the developed method was investi-

    gated by analyzing a certified reference material (DORM-2). Melo et al. (46)

    developed an ultrasound-assisted metal extraction with an aqueous solution of

    tertiary amines (CFA-C reagent) in the presence of hydrogen peroxide for

    improving metal solubilization in fish samples. The optimization was carried

    out using a factorial design. The proposed procedure made possible the quanti-

    tative extraction of Ca, Cu, Fe, Mg, and Zn. Accuracy was evaluated by com-

    parison with total acid digestion of the sample in a Parr bomb and using a CRM

    (fish homogenate, MA-A-2, IAEA). All results were in agreement at a 95% con-

    fidence level according to a paired-t test.

    Three different ultrasonic-based sample treatment approaches, automated

    ultrasonic slurry sampling, ultrasound-assisted acid solid-liquid extraction

    (ASLE), and enzymatic probe sonication (EPS), were compared for the determi-

    nation of Cd and Pb by GF AAS in biological reference materials (47). The

    sample mass chosen to perform the analysis was 10 mg and the liquid volume

    was 1 mL of 1 mol L21 nitric acid. Optimum performance (total metal extrac-

    tion) of ultrasound-assisted ASLE for Cd was only achieved in two of the four

    materials investigated, and total Pb recovery was only possible in three of the

    five samples. Total extraction with the enzymatic probe sonication was only

    obtained for Cd in oyster tissue. Neither ASLE nor EPS were able to extract

    Cd or Pb from spruce needles. Pb concentration obtained after EPS was

    found to be highly dependent on sample centrifugation speed and time.

    Krishna and Arunachalam (48) investigated the application of an ultra-

    sound-assisted extraction procedure for the determination of major, minor,

    and trace elements in lichen and mussel tissue as a possible alternative to con-

    ventional digestion methods. ICP-MS and ICP OES were used for the quanti-

    fication of the elements. Parameters affecting extraction, such as extractant

    Determination of Metals in Foods 79

  • Dow

    nloa

    ded

    By:

    [Kor

    n, M

    aria

    das

    Gra

    as

    And

    rade

    ] At:

    13:3

    0 6

    Febr

    uary

    200

    8

    concentration, sonication time, and ultrasound amplitude, were optimized to

    get quantitative recovery of elements. These studies indicate that the

    method is fast (within 15 min including centrifugation time) and simple for

    the determination of Na, K, Ca, Mg, Cr, Mn, Co, Ni, Cu, Zn, Ge, As, Se,

    Rb, Sr, Zr, Ag, Cd, In, Sb, Cs, Ba, Pb, and Bi. Quantitative recoveries were

    obtained for most of the elements for which certified concentrations were

    available using a 1% (v/v) HNO3 as extractant and metal solubilizationcould be achieved within 4-min sonication time at 40% sonication

    amplitude and 100 mg sample weight. An overall precision of better than

    10% could be achieved for many elements in multiple extractions. Closed-

    microwave digestion method was also used for the estimation of various

    elements in lichen and mussel samples for comparison.

    A new sample preparation procedure for elemental characterization,

    involving acid extraction of the analytes from onion cultivar samples by

    means of an ultrasonic bath, was proposed by Alvarez et al. (49). The

    technique of total reflection X-ray fluorescence was successfully applied for

    the simultaneous determination of Ca, K, Mn, Fe, Cu, and Zn. The procedure

    was compared with wet and dry ashing procedures for all the elements using

    multivariate analysis and the Scheffe test. The FAAS technique was

    employed for comparison purposes and accuracy evaluation of the proposed

    analytical method. Good agreement between the two techniques was found

    when using the dry ashing and ultrasonic leaching procedures.

    Slurry Sample Preparation

    Slurry sampling was considered to have certain advantages over direct solid

    sampling, since it is possible to change the slurry concentration by simple

    dilution, hence combining the advantages of solid and liquid sampling.

    Another advantage that has been claimed is that aqueous standards may be

    used for calibration. However, the stabilization of the slurry, its homogeneity,

    particle size, and sedimentation also have to be considered.

    Li and Jiang (50) used an electrothermal vaporization dynamic reaction

    cell ICP-MS to determine trace elements in rice slurry samples. The

    influence of instrument operating conditions and slurry preparation on the

    ion signals was investigated. Since the sensitivities of Cr, Cu, Cd, Hg, and

    Pb in the rice flour slurry and aqueous solution were quite different,

    standard addition and isotope dilution methods were used for the determi-

    nation of these elements in NIST SRM 1568a rice flour CRM and two rice

    samples purchased from the market. The analytical results for the CRM

    agreed with the certified values. The results for the rice samples, for which

    no reference values were available, were also found to be in good

    agreement between the isotope dilution and standard addition methods.

    Vinas et al. (51) developed a rapid and accurate procedure for the deter-

    mination of Se, Cd, and Pb in different types of baby food using slurry

    M. das G. A. Korn et al.80

  • Dow

    nloa

    ded

    By:

    [Kor

    n, M

    aria

    das

    Gra

    as

    And

    rade

    ] At:

    13:3

    0 6

    Febr

    uary

    200

    8

    sampling and GF AAS. Suspensions prepared in a medium containing 0.1%

    (w/v) Triton X-100, 30% (v/v) concentrated hydrogen peroxide, 1% (v/v)concentrated nitric acid and a chemical modifier (0.5% (w/v) nickel for Se,0.2% (w/v) nickel plus 1% (w/v) ammonium dihydrogenphosphate for Cd,and 1% (w/v) ammonium dihydrogenphosphate for Pb) were introduceddirectly into the furnace. Calibration with aqueous standard solutions was

    used for the determination of Se and Pb, while the standard addition

    technique was used for Cd determination. The reliability of the procedures

    was established by comparing the results obtained with those found for five

    fish-based baby foods after MW-assisted digestion and by analyzing six bio-

    logical CRM. The results showed that no previous sample mineralization was

    necessary because the experimental procedure was simple, which reduces the

    risks of contamination and loss through volatilization.

    Silva et al. (52) developed a method to determine Mn and Zn in powdered

    chocolate samples by slurry sampling FAAS. The optimized conditions,

    which were established using univariate methodology, were a sample mass

    of 150 mg, 2.0 mol L21 nitric acid solution, sonication time of 15 min, and

    a slurry volume of 50 mL. The analytical results were compared with those

    obtained after open vessel and acid bomb digestion procedures and determi-

    nation using FAAS. The statistical comparison by t-test (95% confidence

    level) showed no significant difference between these results.

    Lopez-Garca et al. (53) proposed a procedure for GF AAS determination

    of phosphorus in honey, milk, and infant formulas using slurry sampling. Sus-

    pensions prepared in a medium containing 50% v/v concentrated hydrogenperoxide, 1% v/v concentrated nitric acid, 10% m/v glucose, 5% m/vsucrose, and 100 mg L21 of potassium were introduced directly into the

    furnace. Calibration was performed using aqueous standards prepared in the

    same suspension medium and the analytical curve was linear between 5 and

    80 mg L21 P. The reliability of the procedure was checked by comparing

    the results obtained by the proposed method with those found with a

    reference spectrophotometric method after mineralization and by analyzing

    several CRM. Cava-Montesinos et al. (54) developed a simple and fast

    procedure for the determination of As, Sb, Se, Te, and Bi in milk samples

    by HG AFS. Samples were treated with aqua regia for 10 min in an ultrasound

    water bath and pre-reduced with KBr for total Se and Te determination or with

    KI and ascorbic acid for total As and Sb; the determination of Bi was possible

    with or without pre-reduction. Slurries of samples, in the presence of

    Antifoam A, were treated with NaBH4 in HCl medium to form the correspond-

    ing hydrides, and the calibration solutions were prepared and measured in the

    same way as samples. Results obtained by the developed procedure compared

    well with those found after MW-assisted digestion of samples. The proposed

    method is simple and fast, and only 1 mL of milk is required.

    Anthemidis and Pliatsika (55) developed a simple on-line slurry formation

    and direct nebulization system for multi-element analysis of cocoa and coffee

    powder samples by ICP OES. A laboratory-made microchamber with a

    Determination of Metals in Foods 81

  • Dow

    nloa

    ded

    By:

    [Kor

    n, M

    aria

    das

    Gra

    as

    And

    rade

    ] At:

    13:3

    0 6

    Febr

    uary

    200

    8

    magnetic stirrer was used for on-line slurry formation in a dispersant solution of

    0.5% v/v Triton X-100 and 1% v/v HNO3. A Babington-type nebulizercombined with cyclonic-type spray chamber was adopted for on-line slurry neb-

    ulization. The recommended particle size was ,70 mm and the slurry concen-tration was 0.6%m/v, while the working slurry concentration could range from0.3 to 3.3% m/v with proportional sensitivity. Excellent agreement was foundbetween the standard addition calibration procedure and calibration against

    aqueous standard solutions for almost all of the investigated elements. The

    reliability of the proposed method was confirmed by comparing it with FAAS

    and GF AAS after wet digestion and no significant differences were observed

    between the two methods.

    A simple method combining slurry sampling after cryogenic grinding and

    the use of a permanent modifier was proposed for the determination of Cd and

    Pb in foods by GF AAS (56). The potentialities of cryogenic grinding were

    evaluated for different materials that are difficult to homogenize, such as

    high-fat and high-fiber tissues. Animal and vegetal samples were cut into

    small pieces and ground in liquid nitrogen for 2 min. Slurries were prepared

    directly in the autosampler cup by transferring an exact amount of ground

    material (520 mg) to the cup, followed by 1.00 mL of 0.2% (v/v) HNO3containing 0.04% (v/v) Triton X-100 and sonication for 30 s, before transfer-ring onto the platform that has previously been coated with 250 mg W and200 mg Rh. No statistical differences were found by the paired t-test at the95% level between the results for Cd and Pb in foods slurries and those

    obtained with digested samples.

    Santos et al. (57) tested five different slurry preparation procedures for

    fish tissue samples after grinding the solid samples to a particle size of

    53 mm: (1) using aqua regia plus HF, 30 min of sonication, standing time of24 h followed by another 30 min of sonication; (2) same as the previous

    one, except that the standing time and the second ultrasound treatment were

    omitted; (3) same as the previous one, except that HF was not used; (4)

    same as the previous one, except that the aqua regia was replaced by nitric

    acid; (5) same as the previous one, except that the nitric acid was replaced

    by tetramethylammonium hydroxide (TMAH). The Hg vapor was generated

    in a continuous-flow system and the emission signal intensity measured on-

    line at 253.652 nm by axial view ICP OES. The first three procedures

    produced results in agreement with the certified values. The two last pro-

    cedures using nitric acid or TMHA could not be used for quantitative determi-

    nation. For practical reasons, Procedure 3, with a detection limit (3 s, n 10)of 0.06 microgram per gram for a sample mass of 20 mg in a final volume of

    15 mL was recommended, because it was simple, rapid, and robust.

    Bugallo et al. (58) developed a slurry sampling method for the determi-

    nation of Ca, Cu, Fe, Mg, and Zn in fish tissue samples by FAAS. In compari-

    son with microwave-assisted digestion, the proposed method was simple,

    required only a short time, and eliminated total sample dissolution before

    analysis. The suspension medium was optimized for each analyte to obtain

    M. das G. A. Korn et al.82

  • Dow

    nloa

    ded

    By:

    [Kor

    n, M

    aria

    das

    Gra

    as

    And

    rade

    ] At:

    13:3

    0 6

    Febr

    uary

    200

    8

    quantitative recoveries from fish tissue samples without interferences.

    However, Fe recoveries were not higher than 46%. Treatment of samples

    suspended in nitric acid by MW irradiation for 1530 s at 75285 W

    permitted achieving efficient recoveries for Ca, Fe, Mg, and Zn. Further

    reduction of matrix effects for iron determination was accomplished by the

    use of an additional short step of MW-assisted slurry treatment. However,

    use of the standard addition technique was required for Ca and Cu determi-

    nation, and hydrochloric acid had to be used as suspension medium for the

    last one. The standard deviations obtained using slurry sampling method

    and MW-assisted digestion were not significantly different, and the mean

    relative standard deviation of the overall method (n 3) of the slurrysampling method for different concentration levels was less than 12%.

    DIRECT SOLID SAMPLING ANALYSIS

    Direct solid sampling (SS) analysis is the oldest technique for the determi-

    nation of metals by spectrometric techniques using arc or spark emission

    and, together with X-ray fluorescence spectrometry, it is still the most

    widely used technique in metallurgical laboratories nowadays. Among the

    techniques that can be used for direct SS in combination with AAS, ICP

    OES, and ICP-MS are laser ablation and electrothermal atomization or vapor-

    ization. From these alternatives, GF AAS has been shown to be the most

    attractive technique for the direct analysis of solid samples, mainly because

    of the absence of a nebulizer system, which simplifies the introduction of

    the solid material into the atomizer. Direct SS analysis offers a number of

    advantages, such as the reduced sample preparation time and hence a faster

    analysis; higher accuracy, as errors due to analyte loss and/or contaminationare dramatically reduced; higher sensitivity due to the absence of any dilution;

    and the absence of any corrosive or toxic waste. Another advantage is the long

    residence time of the sample in the GF AAS atomizer, which usually makes

    possible complete volatilization of the particles independent of their size

    and complete atomization of the analyte. Moreover, it shows quite low

    limits of detection, which is highly desirable in trace analysis. Most of the dis-

    advantages that have been mentioned for direct SS analysis using GF AAS are

    actually no longer valid. There are reliable tools available nowadays both for

    manual and automatic introduction of solid samples into the graphite furnace,

    and it has been shown that in most cases aqueous standards can be used for

    calibration also in direct SS analysis. The only limitations that have to be

    mentioned are the relatively short linear working range of AAS, which

    usually limits direct SS analysis to the determination of low trace concen-

    trations, and the imprecision of the results, which is typically of the order

    of 10% due to the inhomogeneity of natural samples (59).

    Flores et al. (60) developed a new device to introduce solid biological test

    samples directly into the flame of an AAS instead of the traditional

    Determination of Metals in Foods 83

  • Dow

    nloa

    ded

    By:

    [Kor

    n, M

    aria

    das

    Gra

    as

    And

    rade

    ] At:

    13:3

    0 6

    Febr

    uary

    200

    8

    introduction systems and also to avoid prior sample combustion-vaporization.

    Copper was determined directly in bovine liver samples by FAAS without the

    need of extraction, digestion, or slurry preparation. Between 0.05 and 0.50 mg

    of the test sample was weighed directly into a small polyethylene vial

    connected to a glass chamber. A flow of air carries the test sample as a dry

    aerosol to a T-shaped quartz cell positioned in the optical path above the

    burner. The atomic vapor generated produced a transient signal of less than

    3 s duration; integrated absorbance was used for signal evaluation. The

    results were compared with those obtained after a conventional sample

    digestion and there was no statistical difference between the results from

    the proposed system and those obtained after digestion and determination

    by conventional FAAS. No excessive grinding of the samples was required

    and samples with particle size less than 80 mm were used throughout. Back-ground signals were always low and a characteristic mass of 1.5 ng was

    found for Cu. The proposed system allows the determination of 60 test

    samples in 1 h and it can be easily adapted to conventional atomic absorption

    spectrometers.

    Detcheva and Grobecker (61) developed direct SS methods for GF AAS

    and applied these to the determination of Hg, Cd, Mn, Pb, and Sn in seafood.

    All elements except for Hg were measured using a third-generation Zeeman-

    effect AAS combined with an automatic solid sampler. The calibration range

    was substantially extended using the three-field and dynamic mode and high

    analyte masses could be determined without laborious dilution of solid

    samples. The measurements were based on calibration with CRM of

    organic matrices. In case solid CRM were not available, calibration with

    aqueous standard solutions was proved to be an alternative. No matrix

    effects were observed under optimized conditions and results were in good

    agreement with the certified values. Direct SS-GF AAS with Zeeman-effect

    background correction proved to be a reliable, rapid, and low-cost method

    for the control of trace elements in seafood.

    Grobecker and Detcheva (62) validated the determination of total

    mercury by direct SS-GF AAS with Zeeman-effect background correction

    and a specially designed furnace using CRM of different origin. The tempera-

    ture program provided only one stage; atomization of mercury and pyrolysis

    of the matrix was performed at a constant temperature in the range of 900

    10008C. A calibration curve established using aqueous solutions and solidCRM; all points were covered by one line, indicating that mercury determi-

    nation was matrix independent using this technique. Even relatively high

    amounts of chlorine, which are known for causing problems in mercury deter-

    mination, did not influence analytical results. The accuracy of the method

    became evident when comparing certified and experimental values. The

    precision of the measurements in a range from 0.5 to 50 ng Hg did not

    exceed 3% RSD.

    Oleszczuk et al. (63) developed a method for the determination of cobalt,

    copper, and manganese in green coffee using direct SS-GF AAS. The authors

    M. das G. A. Korn et al.84

  • Dow

    nloa

    ded

    By:

    [Kor

    n, M

    aria

    das

    Gra

    as

    And

    rade

    ] At:

    13:3

    0 6

    Febr

    uary

    200

    8

    used a number of botanical CRM and preanalyzed samples of green coffee for

    method validation, and ICP OES after MW-assisted acid digestion of the

    samples was used as reference method. Manganese and cobalt could be deter-

    mined using aqueous standards for calibration, but calibration with solid CRM

    was necessary for the determination of copper. No significant difference was

    found between the results obtained with the proposed method and certified or

    independently determined values. Seven samples of Brazilian green coffee

    were analyzed, and there was no significant difference between the values

    obtained with SS-GF AAS and ICP OES for Mn and Cu. Hence, a single-

    element technique that does not require any sample preparation besides

    grinding of the coffee beans appears to be an attractive alternative to the

    multi-element techniques that have been used up to now. The much better sen-

    sitivity of this technique is an additional advantage in the determination of

    trace elements such as cobalt and others that might be of importance.

    Oliveira et al. (64) investigated systematically sample preparation and

    micro-homogeneity for the determination of Cd and Pb in bovine liver using

    direct SS-GF AAS. Two different procedures for sample preparation have been

    investigated: (a) drying in a household microwave oven followed by drying in

    a stove at 608C to constant mass and (b) freeze drying; ball and cryogenicmills were used for grinding. Particle size, sample size, and microsample hom-

    ogeneity were investigated. All samples showed good homogeneity (He , 10)even for low sample mass, but samples dried in a microwave oven/stove andground in a ball mill presented the best homogeneity. The results obtained

    with both methods of sample preparation indicated the possibility to produce

    bovine liver of reference for determination of Cd and Pb by SS-GF AAS.

    A very interesting series of studies about direct SS-GF AAS has been

    carried out by Lucker et al. (6570) between 1987 and 1999, investigating

    the possibility of analyzing fresh meat for contaminants as kind of a

    screening method to be carried out directly in the slaughterhouse. This idea

    has been picked up recently by Damin et al. (71) in order to find out if this

    technique could be used within the Brazilian program of residue control in

    products of animal origin. The authors investigated the determination of Cd

    and Pb in fresh meat, which was weighed directly onto the SS platform

    using palladium and magnesium nitrates as a mixed modifier. The results

    were in good agreement with those obtained after acid digestion, taking into

    account the average humidity of 27+ 2% of fresh meat. Aqueous standardscould be used for calibration and the limits of detection of 0.13 mg kg21 forCd and 1.9 mg kg21 for Pb as well as the average RSD of 14% were morethan adequate for the purpose.

    The recently introduced technique of high-resolution continuum source

    (HR-CS) AAS (7274) appears to offer even greater advantages for direct

    SS-GF AAS, as the entire spectral environment of the analytical line becomes

    visible at high resolution. This feature makes it possible to detect and avoid

    spectral interferences and the system also offers new possibilities to correct

    for spectral interferences and is greatly facilitating method development (72).

    Determination of Metals in Foods 85

  • Dow

    nloa

    ded

    By:

    [Kor

    n, M

    aria

    das

    Gra

    as

    And

    rade

    ] At:

    13:3

    0 6

    Febr

    uary

    200

    8

    Ribeiro et al. (75) investigated the determination of Co in fish and other biologi-

    cal samples comparing direct SS-GF AAS and alkaline treatment with TMAH

    and conventional line source GF AAS with HR-CS GF AAS. Method develop-

    ment was found to be much easier using HR-CS AAS, and the best LOD of 5 ng

    g21 was obtained with direct SS and HR-CS GF AAS.

    Borges et al. (76) used HR-CS GF AAS for the determination of Pb in fish

    and meat CRM using direct SS analysis. Ruthenium was used as a permanent

    modifier, and the 217.001-nm resonance line was used for the determination

    because of its better signal-to-noise ratio with HR-CS AAS. Under

    optimized conditions the electron excitation spectrum of the PO molecule

    with rotational fine structure could be separated in time from the Pb absorption

    signal, avoiding any spectral interference. A limit of detection of 10 ng g21

    could be obtained and the precision was typically better than 10% RSD.

    The values obtained in seven CRM were in agreement with the certified

    values according to the t-test for a 95% confidence level.

    Da Silva et al. (77) investigated the determination of Hg in fish and meat

    CRM using direct SS analysis with HR-CS GF AAS. Initial experiments

    indicated that it was not possible to use a chemical modifier for this kind of

    analysis, as in this case the Hg absorption peak would coincide with the

    excessive background absorption caused by the organic matrix. It was also

    found that without a modifier Hg from fish samples was already lost at temp-

    eratures around 1008C, as it is mostly present as methyl mercury in this matrix,which is much more volatile than inorganic Hg. The authors finally used a

    temperature program without a pyrolysis stage, using only a drying stage of

    3 s at 1008C, followed directly by the atomization stage at 11008C. Underthese conditions the Hg signal appeared before the background and could

    be separated because of the superior background correction capabilities of

    HR-CS AAS. Aqueous standards were used for calibration, which had to be

    stabilized with potassium permanganate in order to avoid losses of Hg in

    the drying stage. Good agreement was found between determined and

    certified values for six CRM according to the t-test for a 95% confidence

    level. The precision, expressed as RSD, was typically around 5% and the

    detection limit was determined as 0.1 mg g21 Hg in the solid sample.

    CONCLUSION

    Assured information about metal concentration in food samples is essential

    from the society from the nutritional, technological and toxicological point

    of view. Atomic and inorganic mass spectrometric techniques , after appropri-

    ate sample preparation, are most frequently used in order to obtain the required

    and reliable information about metals in foods, particularly at trace levels.

    Ultratrace species need particular laboratorial structures.

    In this perspective, the integrity of chemical information is strongly

    dependent on the prior analytical steps and an adequate selection of sample

    M. das G. A. Korn et al.86

  • Dow

    nloa

    ded

    By:

    [Kor

    n, M

    aria

    das

    Gra

    as

    And

    rade

    ] At:

    13:3

    0 6

    Febr

    uary

    200

    8

    preparation procedure is of capital importance. It was observed that different

    sample preparation procedures have been successfully applied for determi-

    nation of a wide variety of elements in diverse food samples and the trends

    are to minimize sample handling and reagent consumption in order to

    reduce sample contamination and to improve analytical throughput. In this

    sense, direct solid analysis and slurry analysis have obtained special interest

    of analytical chemists since they cover the mentioned sample preparation

    trends.

    ACKNOWLEDGMENTS

    The authors are grateful to the CNPq (Conselho Nacional de Desenvolvimento

    Tecnologico, Braslia, Brazil) and FAPESB (Fundacao de Amparo a Pesquisa

    do Estado da Bahia, Salvador, Brazil) for fellowships and financial supports.

    REFERENCES

    1. Arruda, M.A.Z. (2007) Trends in Sample Preparation; Nova Science Publishers:New York.

    2. Sneddon, J., Hardaway, C., Bobbadi, K.K., and Reddy, A.K. (2006) Sample prep-aration of solid samples for metal determination by atomic spectroscopyAnoverview and selected recent applications. Applied Spectroscopy Reviews, 41:114.

    3. Buldini, P.L., Ricci, L., and Sharma, J.L. (2002) Recent applications of samplepreparation techniques in food analysis. Journal of Chromatography A, 975:4770.

    4. Luque de Castro, M.D. and Capote, F.P. (2007) Analytical Applications of Ultra-sound; Elsevier: Amsterdam.

    5. Kurfurst, U. (1998) Solid Sample AnalysisDirect and Slurry Sampling UsingGF-AAS and ETV-ICP; Springer: Berlin.

    6. Hoenig, M. (2001) Preparation steps in environmental trace element analysisFacts and traps. Talanta, 54: 10211038.

    7. Tuzen, M. (2003) Determination of heavy metals in fish samples of the middleBlack Sea (Turkey) by graphite furnace atomic absorption spectrometry. FoodChemistry, 80 (1): 119123.

    8. Saracoglu, S., Saygi, K.O., Uluozlu, O.D., Tuzen, M., and Soylak, M. (2007)Determination of trace element contents of baby foods from Turkey. FoodChemistry, 105 (1): 280285.

    9. Tuzen, M., Silici, S., Mendil, D., and Soylak, M. (2007) Trace element levels inhoneys from different regions of Turkey. Food Chemistry, 103 (2): 325330.

    10. Mindak, W.R. and Dolan, S.P. (1999) Determination of arsenic and selenium infood using a microwave digestionDry ash preparation and flow injectionhydride generation atomic absorption spectrometry. Journal of Food Compositionand Analysis, 12: 111122.

    Determination of Metals in Foods 87

  • Dow

    nloa

    ded

    By:

    [Kor

    n, M

    aria

    das

    Gra

    as

    And

    rade

    ] At:

    13:3

    0 6

    Febr

    uary

    200

    8

    11. Welz, B. and Sperling, M. (1999) Atomic Absorption Spectrometry; Wiley-VCH:

    Weinheim.

    12. Momen, A.A., Zachariadis, G.A., Anthemidis, A.N., and Stratis, J.A. (2007) Use of

    fractional factorial design for optimization of digestion procedures followed by

    multi-element determination of essential and non-essential elements in nuts

    using ICP-OES technique. Talanta, 71 (1): 443451.

    13. Momen, A.A., Zachariadis, G.A., Anthemidis, A.N., and Stratis, J.A. (2006) Inves-

    tigation of four digestion procedures for multi-element determination of toxic andnutrient elements in legumes by inductively coupled plasma-optical emission spec-

    trometry. Analytica Chimica Acta, 565 (1): 8188.

    14. Boutakhrit, K., Claus, R., Bolle, F., Degroodt, J.M., and Goeyens, L. (2005) Open

    digestion under reflux for the determination of total arsenic in seafood by induc-

    tively coupled plasma atomic emission spectrometry with hydride generation.

    Talanta, 66 (4): 10421047.

    15. Tinggi, U., Reillyb, C., and Pattersod, C. (1997) Determination of manganese and

    chromium in foods by atomic absorption spectrometry after wet digestion. Food

    Chemistry, 60 (1): 123128.

    16. Olivares, M., Pizarro, F., and Pablo, S. (2004) Iron, zinc, and copper: contents in

    common Chilean foods and daily intakes in Santiago, Chile. Nutrition, 20 (2):

    205212.

    17. Cabrera, C., Lloris, F., Gimenez, R., Olalla, M., and Lopez, M.C. (2003) Mineralcontent in legumes and nuts: contribution to the Spanish dietary intake. Science of

    the Total Environment, 308: 114.

    18. Kira, C.S., Maio, F.D., and Maihara, V.A. (2004) Comparison of partial digestion

    procedures for determination of Ca, Cr, Cu, Fe, K, Mg, Mn, Na, P, and Zn in milk

    by inductively coupled plasma-optical emission spectrometry. Journal of AOAC

    International, 87 (1): 151156.

    19. Rodriguez, E.M.R., Sanzalaejos, M., and Romero, C.D. (2001) Mineral concen-

    trations in cows milk from the Canary Island. Journal of Food Composition

    and Analysis, 14 (4): 419430.

    20. Cava-Montesinos, P., Cervera, M.L., Pastor, A., and Guardia, M. (2003) Hydride

    generation atomic fluorescence spectrometric determination of ultratraces of

    selenium and tellurium in cow milk. Analytica Chimica Acta, 481 (2): 291300.21. Ferreira, K.S., Gomes, J.C., and Chaves, J.B.P. (2005) Copper content of

    commonly consumed food in Brazil. Food Chemistry, 92 (1): 2932.

    22. Santos, W.P.C., Teixeira, A.P., Gramacho, D.R., Costa, A.C.S., and Korn, M.G.A.

    Use of Doehlert design for optimizing the digestion of beans for multi-element

    determination by inductively coupled plasma optical emission spectrometry.

    Journal of the Brazilian Chemical Society, 19 (1): 110.

    23. Doner, G. and Ege, A. (2004) Evaluation of digestion procedures for the determi-

    nation of iron and zinc in biscuits by flame atomic absorption spectrometry.

    Analytica Chimica Acta, 520 (12): 217222.

    24. Jalbani, N., Kazi, T.G., Jamali, M.K., Arain, B.M., Afridi, H.I., and Baloch, A.

    (2007) Evaluation of aluminum contents in different bakery foods by electrother-

    mal atomic absorption spectrometer. Journal of Food Composition and Analysis,

    20 (34): 226231.25. Costa, L.M., Korn, M.G.A., Castro, J.T., dos Santos, W.P.C., Carvalho, E.V., and

    Nogueira, A.R.A. (2006) Planejamento fatorial aplicado a` digestao de amostras de

    feijao assistida por radiacao microondas. Quimica Nova, 29 (1): 149152.

    26. Santelli, R.E., Bezerra, M.A., SantAna, O.D., Cassella, R.J., and Ferreira, S.L.C.

    (2006) Multivariate technique for optimization of digestion procedure by

    M. das G. A. Korn et al.88

  • Dow

    nloa

    ded

    By:

    [Kor

    n, M

    aria

    das

    Gra

    as

    And

    rade

    ] At:

    13:3

    0 6

    Febr

    uary

    200

    8

    focussed microwave system for determination of Mn, Zn and Fe in food samples

    using FAAS. Talanta, 68: 10831088.

    27. Nookabkaew, S., Rangkadilok, N., and Satayavivad, J. (2006) Determination of

    trace elements in herbal tea products and their infusions consumed in Thailand.

    Journal of Agricultural and Food Chemistry, 54: 69396944.

    28. Costa, L.M., Gouveia, S.T., and Nobrega, J.A. (2002) Comparison of heating

    extraction procedures for Al, Ca, Mg, and Mn in tea samples. Analytical

    Sciences, 18 (3): 313318.

    29. Cubadda, F. and Raggi, A. (2005) Determination of cadmium, lead, iron, nickel

    and chromium in selected food matrices by plasma spectrometric techniques.

    Microchemical Journal, 79 (12): 9196.

    30. Cubadda, F., Raggi, A., and Marconi, E. (2005) Effects of processing on five

    selected metals in the durum wheat food chain. Microchemical Journal, 79:

    97102.

    31. Zeiner, M., Steffan, I., and Cindric, I.J. (2005) Determination of trace elements in

    olive oil by ICP-AES and ETA-AAS: A pilot study on the geographical character-

    ization. Microchemical Journal, 81: 171176.

    32. Cindric, I.J., Zeiner, M., and Steffan, I. (2007) Trace elements characterization in

    edible oil by ICP-AES and GFAAS: A pilot study on the geographical character-

    ization. Microchemical Journal, 85: 136139.

    33. Santos, D.M., Pedroso, M.M., Costa, L.M., Nogueira, A.R.A., and Nobrega, J.A.

    (2005) A new procedure for bovine milk digestion in a focused microwave

    oven: Gradual sample addition to pre-heated acid. Talanta, 65: 505510.

    34. Matusiewicz, H. and Stanisz, E. (2007) Characterization of a novel UV-TiO2-

    microwave integrated irradiation device in decomposition process.Microchemical

    Journal, 86: 916.

    35. Yaman, M., Durak, M., and Bakirdere, S. (2005) Comparison of dry, wet, and

    microwave ashing methods for the determination of Al, Zn, and Fe in yogurt

    samples by atomic absorption spectrometry. Spectroscopy Letters, 38 (45):

    405417.

    36. Trevizan, L.C., Nogueira, A.R.A., and Nobrega, J.A. (2003) Single vessel

    procedure for acid vapor partial digestion of bovine liver in a focused

    microwave: Multielement determination by ICP-OES. Talanta, 61: 8186.

    37. Yebra-Biurrun, M.C. and Garcia-Garrido, A. (2001) Continuous flow systems for

    the determination of trace elements and metals in seafood. Food Chemistry, 72:

    279287.

    38. Cid, B.P., Boia, C., Pombo, L., and Rebelo, E. (2001) Determination of trace

    metals in fish species of the Ria de Aveiro (Portugal) by electrothermal atomic

    absorption spectrometry. Food Chemistry, 75 (1): 93100.

    39. Liang, L.N., Jiang, G.B., Liu, J.F., and Hu, J.T. (2003) Speciation analysis of

    mercury in seafood by using high-performance liquid chromatography on-line

    coupled with cold-vapor atomic fluorescence spectrometry via a post column

    microwave digestion. Analytica Chimica Acta, 477: 131137.

    40. Serafimovski, I., Karadjova, I.B., Stafilov, T., and Tsalev, D.L. (2006) Determi-

    nation of total arsenic and toxicologically relevant arsenic species in fish by

    using electrothermal and hydride generation atomic absorption spectrometry.

    Microchemical Journal, 83: 5560.

    41. Mesko, M.F., Moraes, D.P., Barin, J.S., Dressler, V.L., Knapp, G., and

    Flores, E.M.M. (2006) Digestion of biological materials using the microwave-

    assisted sample combustion technique. Microchemical Journal, 82: 183188.

    Determination of Metals in Foods 89

  • Dow

    nloa

    ded

    By:

    [Kor

    n, M

    aria

    das

    Gra

    as

    And

    rade

    ] At:

    13:3

    0 6

    Febr

    uary

    200

    8

    42. Araujo, G.C.L., Gonzalez, M.H., Ferreira, A.G., Nogueira, A.R.A., and

    Nobrega, J.A. (2002) Effect of acid concentration on closed-vessel microwave-

    assisted digestion of plant materials. Spectrochimica Acta, 57B (12): 21212132.

    43. Korn, M., Santos Junior, D., and Krug, F.J. (2006) Currents on ultrasound-assisted

    extraction for sample preparation and spectroscopic analytes determination.

    Applied Spectroscopy Reviews, 41: 305321.44. Nascentes, C.C., Korn, M., and Arruda, M.A.Z. (2001) A fast ultrasound-assisted

    extraction of Ca, Mg, Mn and Zn from vegetables. Microchemical Journal, 69:

    3743.

    45. Manutsewee, N., Aeungmaitrepirom, W., Varanusupakul, P., and Imyim, A.

    (2007) Determination of Cd, Cu, and Zn in fish and mussel by AAS after ultra-

    sound-assisted acid leaching extraction. Food Chemistry, 101 (2): 817824.

    46. Melo, M.H.A., Costa, A.C.S., Nobrega, J.A., and Ferreira, S.L.C. (2005) The use

    of water soluble tertiary amine reagent for solubilization and metal determination

    in fish muscle tissue. Journal of the Brazilian Chemical Society, 16 (1): 6973.47. Maduro, C., Vale, G., Alves, S., Galesio, M., da Silva, M.D.R.G., Fernandez, C.,

    Catarino, S., Rivas, M.G., Mota, A.M., and Capelo, J.L. (2006) Determination of

    Cd and Pb in biological reference materials by electrothermal atomic absorption

    spectrometry: A comparison of three ultrasonic-based sample treatment pro-

    cedures. Talanta, 68 (4): 11561161.

    48. Balarama Krishna, M.V. and Arunachalam, J. (2004) Ultrasound-assisted extrac-

    tion procedure for the fast estimation of major, minor and trace elements in

    lichen and mussel samples by ICP-MS and ICP-AES. Analytica Chimica Acta,

    522 (2): 179187.49. Alvarez, J., Marco, L.M., Arroyo, J., Greaves, E.D., and Rivas, R. (2003) Determi-

    nation of calcium, potassium, manganese, iron, copper and zinc levels in represen-

    tative samples of two onion cultivars using total reflection X-ray fluorescence and

    ultrasound extraction procedure. Spectrochimica Acta B, 58 (12): 21832189.

    50. Li, P.C. and Jiang, S.J. (2003) Electrothermal vaporization inductively coupled

    plasma-mass spectrometry for the determination of Cr, Cu, Cd, Hg and Pb in

    rice flour. Analytica Chimica Acta, 495: 143150.

    51. Vinas, P., Martnez, M.P., and Cordoba, M.H. (2000) Rapid determination of

    selenium, lead and cadmium in baby food samples using electrothermal atomicabsorption spectrometry and slurry atomization. Analytica Chimica Acta, 412:

    121130.

    52. Silva, E.G.P., Santos, A.C.N., Costa, A.C.S., Fortunato, D.M.N., Jose, N.M.,

    Korn, M.G.A., Santos, W.N.L., and Ferreira, S.L.C. (2006) Determination of

    manganese and zinc in powdered chocolate samples by slurry sampling using

    sequential multi-element flame atomic absorption spectrometry. Microchemical

    Journal, 82 (2): 159162.

    53. Lopez-Garca, I., Vinas, P., Romero-Romero, R., and Hernandez-Cordoba, M.

    (2007) Fast determination of phosphorus in honey, milk and infant formulas by

    electrothermal atomic absorption spectrometry using a slurry samplingprocedure. Spectrochimica Acta B, 62: 4855.

    54. Cava-Montesinos, P., Cervera, M.L., Pastor, A., and de la Guardia, M. (2004)

    Determination of As, Sb, Se, Te and Bi in milk by slurry sampling hydride gener-

    ation atomic fluorescence spectrometry. Talanta, 62: 175184.

    55. Anthemidis, A.N. and Pliatsika, V.G. (2005) On-line slurry formation and nebuli-

    zation for inductively coupled plasma atomic emission spectrometry. Multi-

    element analysis of cocoa and coffee powder samples. Journal of Analytical

    Atomic Spectrometry, 20: 12801286.

    M. das G. A. Korn et al.90

  • Dow

    nloa

    ded

    By:

    [Kor

    n, M

    aria

    das

    Gra

    as

    And

    rade

    ] At:

    13:3

    0 6

    Febr

    uary

    200

    8

    56. Santos, D. Jr., Barbosa, F. Jr., Tomazelli, A.C., Krug, F.J., Nobrega, J.A., and

    Arruda, M.A.Z. (2002) Determination of Cd and Pb in food slurries by GFAAS

    using cryogenic for sample preparation. Analytical and Bioanalytical Chemistry,

    373: 183189.

    57. dos Santos, E.J., Herrmann, A.B., Vieira, M.A., Frescura, V.L.A., and Curtius, A.J.

    (2005) Evaluation of slurry preparation procedures for the determination of

    mercury by axial view inductively coupled plasma optical emission spectrometry

    using on-line cold vapor generation. Spectrochimica Acta B, 60: 659665.

    58. Bugallo, R.A., Segade, S.R., and Gomez, E.F. (2007) Comparison of slurry

    sampling and microwave-assisted digestion for calcium, magnesium, iron,

    copper and zinc determination in fish tissue samples by flame atomic absorption

    spectrometry. Talanta, 72: 6065.

    59. Vale, M.G.R., Oleszczuk, N., and Santos, W.N.L. (2006) Current status of direct

    solid sampling for electrothermal atomic absorption spectrometryA critical

    review of the development between 1995 and 2005. Applied Spectroscopy

    Reviews, 41: 377400.

    60. Flores, E.M.M., Costa, A.B., Barin, J.S., Dressler, V.L., Paniz, J.N.G., and

    Martins, A.F. (2001) Direct flame solid sampling for atomic absorption spec-

    trometry: Determination of copper in bovine liver. Spectrochimica Acta B, 56:

    18751882.

    61. Detcheva, A. and Grobecker, K.H. (2006) Determination of Hg, Cd, Mn, Pb and Sn

    in seafood by solid sampling Zeeman atomic absorption spectrometry. Spectrochi-

    mica Acta B, 61: 454459.

    62. Grobecker, K.H. and Detcheva, A. (2006) Validation of mercury determination by

    solid sampling Zeeman atomic absorption spectrometry and a specially designed

    furnace. Talanta, 70: 962965.

    63. Oleszczuk, N., Castro, J.T., Silva, M.M., Korn, M.G.A., Welz, B., and

    Vale, M.G.R. Method development for the determination of manganese, cobalt

    and copper in green coffee comparing direct solid sampling electrothermal

    atomic absorption spectrometry and inductively coupled plasma optical emission

    spectrometry Talanta, 73: 862869.

    64. Nomura, C.S. and Oliveira, P.V. (2006) Preparacao de amostra de fgado bovino e

    estudo de micro homogeneidade para a determinacao de Cd e Pb por espectrome-

    tria de absorcao atomica com atomizacao eletrotermica e amostragem direta de

    solido. Quimica Nova, 29 (2): 234239.

    65. Lucker, E., Rosopulo, A., and Kreuzer, W. (1987) Analyses of the distribution of

    lead and cadmium in fresh renal tissue by means of solid sampling Zeeman-AAS.

    Fresenius Zeitschrift fur Analytische Chemie, 328: 370377.

    66. Lucker, E., Gerbig, C., and Kreuzer, W. (1993) Distribution of Pb and Cd in the

    liver of the mallardDirect determination by means of solid sampling ZAAS.

    Fresenius Zeitschrift fur Analytische Chemie, 346: 10621067.

    67. Lucker, E., Meuthen, J., and Kreuzer, W. (1993) Distribution of Pb and Cd in

    equine liverDirect determination by means of solid sampling ZAAS.

    Fresenius Zeitschrift fur Analytische Chemie, 346: 10681071.

    68. Lucker, E. and Schuierer, O. (1996) Sources of error in direct solid sampling

    Zeeman atomic absorption spectrometry analyses of biological samples with

    high water content. Spectrochimica Acta B, 51: 201210.

    69. Lucker, E. (1999) Direct solid sampling ET AAS determination of cadmium in

    equine muscle. Journal of Analytical Atomic Spectrometry, 14: 583587.

    Determination of Metals in Foods 91

  • Dow

    nloa

    ded

    By:

    [Kor

    n, M

    aria

    das

    Gra

    as

    And

    rade

    ] At:

    13:3

    0 6

    Febr

    uary

    200

    8

    70. Lucker, E. (1999) Direct solid sampling ET AAS determination of lead in muscletissue contaminated by gun-shot residues. Journal of Analytical Atomic Spec-trometry, 14: 17311735.

    71. Damin, I.C.F., Silva, M.M., Vale, M.G.R., andWelz, B. (2007) Feasibility of usingdirect determination of cadmium and lead in fresh meat by electrothermal atomicabsorption spectrometry for screening purposes. Spectrochimica Acta B, 62:10371045.

    72. Welz, B., Becker-Ross, H., Florek, S., and Heitmann, U. (2005) High-ResolutionContinuum Source AAS; Wiley-VCH: Weinheim.

    73. Welz, B. (2005) High-resolution continuum source AAS: the better way to performatomic absorption spectrometry. Analytical and Bioanalytical Chemistry, 381:6971.

    74. Welz, B., Borges, D.L.G., Lepri, F.G., Vale, M.G.R., and Heitmann, U. (2007)High-resolution continuum source atomic absorption spectrometryAn analyticaland diagnostic tool for trace analysis. Spectrochimica Acta B, 62: 873883.

    75. Ribeiro, A.S., Vieira, M.A., da Silva, A.F., Borges, D.L.G., Welz, B.,Heitmann, U., and Curtius, A.J. (2005) Determination of cobalt in biologicalsamples by line-source and high-resolution con