aam-wyk2 [tryb zgodności]galaxy.agh.edu.pl/~kca/aam-sem-nas.pdf · Mixed substances may be separate if they differ at least in one physicochemical property. Basic of separation Method

2018-10-29

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W.W.KUBIAK - ADVANCED ANALYTICAL METHODS

ADVANCED ANALYTICAL METHODS

SAMPLE PREPARATION

ANALYTICAL PROCESS


OBJECT OF MESUREMENT

SAMPLE

SIGNAL

RESULT OF MEASUREMENT

RESULT OFANALYSIS

INFORMATION

HIDDENVARIABLES

OBJECT OFINVESTIGATION PROBLEM

STRATEGY OF SAMPLINGSAMPLING

SAMPLE PREPARATION

MEASUREMENT

REGISTRATION/EVALUATION

CALIBRATION

INTERPRETATION

PERCEPTION SOLUTION OF

THE PROBLEM

MEASURINGSYSTEM

CHEMOMETRICMETHODS


SAMPLE PREPARATION

• Homogenization

• Reduction of bulk samples

• Mineralisation

• Dissolution/Digestion/Fusion

• Separation

• Accumulation

• Weighting/Mesurement


SAMPLE MINERALISATION AND DIGESTION

Dry mineralisation (ashing)

OPEN SYSTEM – heating sample in muffle furnace or onburner up to 450 - 550°C (sometimes up to 1000 °C) incrucible (porcelain, quartz, platinum) till all organic matter isdecomposed. Usually proccess takes 3 – 4 hours.


Adventages: method is simple, low blank, unrestrictedsample size

Disadventages: losses of volatile components, possiblemechanical losses, long proccess duration, proccess istwo-stages (ash must be digested/dissolute)

• CLOSED SYSTEM – oxygen bombMethod consisit in deflagration of small amount of organic matter (less than 20

mg) in closed flask with oxygen. Gas products of combustion are absorbed insolution presented in the flask.


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Modern oxygen bombs (Parr)


WET MINERALIZATION

Open system

Mineralization/digestion in acids – heating the sample in oxidatingacids. During proccess inorganic components are digested and organicmatter is oxidized to carbon dioxide, water and other volatile products.Most often are used acids or their mixtures:

HNO3 + H2O2 - biological samplesHNO3 + H2SO4 - universalHNO3 + HCl - aqua regia - universalHNO3 + HClO4 - biological samples, explosiveHF - inorganic samplesHNO3 + HF - universalHClO4 - biological samples, explosive


UV mineralisation – is applicated toliquid samples which contain smallamount of organic matter. Liquidsample is irradiated with UVradiation (quartz lamp usually λ =250 nm, P = 150 W). In most casesthe oxidant (H2O2, K2S2O8, HNO3) isadded to sample in order to facilitatethe process.


Microwave assisted digestion andmineralisation – microwaves arenonionizing irradiation which causemolecular movements such as ionsmigration and dipol rotation. They donot change directly molecular structure.Full frequency range of microwaves is300 - 300000 MHz. However fordigestion and mineralisation applied isfrequency 2450 MHz (the same as inmicrowave oven for kitchen purpose)and source power of 600 - 700 W.


During penetration of the sample by microwave irradiation itis adsorbed in the degree which depends on dissipationfactor. The dissipation factor defines the ability of a mediumto convert electromagnetic energy into heat for a givenfrequency and temperature.Some approximate dissipation factors:0.6 quartz1.5 teflon10 glass1600 waterIn comparison with wet digestion at the heating plate, themicrowave assisted digestion is much faster, becauseenergy is supplied directly to the sample (not through thewalls of container).Applications: biological, geological, environmental andmetalurgical samples.


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MICROWAVE DIGESTION SYSTEM


DIGESTION / MINERALISATION INCLOSED SYSTEM is performed inpressure vassels (bombs orautoclaves) in higher temperature(~125°C) and higher pressure (~0,15MPa). Due to these conditionsproccess is more efficient and faster.Heating may be conventional ormicrowave.Adventages: faster and more efficientproccess. There is no loss of volatilecompounds.


Pressure bomb


Autoclave

FUSION

Some materials are particularly resistant to acid digestion,for example: certain rocks, mineral oxides, phosphates,silicates and some iron alloys. For these samples, high-temperature fusion with an acidic or basic flux in themelted state can be used to render such materials to besoluble in water or dilute acid. Fusion decompositions arethe most rigorous methods available and all silicatematerials, including refractory substances like zircon andcassiterite, can be dissolved completely when fused withan appropriate flux.Disadvantages: contamination because of introduction oflarge amount (10-15 times more than the sample itself) ofsalt (flux).



Pt

Ni

Fe

Au


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SEPARATION AND ACCUMULATION METHODS

Mixed substances may be separate if they differ at least in one physicochemicalproperty.

Basic of separation Method

Volatility DistillationRefining

Partition coefficient (Nernstian)

Chromatography gas-liquidPartition chromatographyExtraction

Equilibrium of exchange Ionic exchange


Surface activity Adsorption chromatographyChromatography gas-solidFoam refining

Molecular geometry Molecular sivesGel filtration/permationGas diffusionInclusion compexesUltrafiltrationDialysis, electrodialysis


Migration Elektrophoresis

Solubility PrecipitationZone refining

Decomposition potential Electrolysis


SEPARATION METHODS


EXTRACTION

Process of mass exchange between two phases:- phase (solid or liquid) from which substance is extracted;- phase (most often liquid called extrahent) to whichsubstance is extracted;performed in the multicomponent system of restrictedsolubility.

Common liquid-liquid extraction system


As the result of the proccess extracted component passes to extrahent in degree described by Nernst division coefficient:

To intensify proccess the complexing agent is added to extrahent phase. In such case the division coefficient is defined as:

Most often extraction is performed in liquid-liquid or solid-liquid system. Recently, especially for chromatography applied is extaction to the solid phase (SPE).


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Extractor (separation funnel) Soxlet apparatus Syringe for SPE


IONIC EXCHANGEReaction A1A2+B1B2=A1B2+B1A2 which is performed at ionexchange resins. They are insoluble in waterpolyelectrolytes (~90% are polystyrenic matrix).Cation exhangers – functional groups -SO3H; -COOHAnion exhangers - functional groups –NH2; =NHGood ion exhange resin should be:chemically resistant,have large exhange capacityreaction of exhange should be fast.Stages of the proccess:

- Exhange metal ions by H+

- Exhange anions by OH-

pure water

- Relase metal ions purging column with acid

- Relase anions purging column with base

Separation

Accumulation


Kolumna jonitowa Ion exhange resin


Laboratory and industrial ion-exhange column

Leakage of column (exceeding capacity of column)


MEMBRANE SEPARATION

W.W.KUBIAK - ADVANCED ANALYTICAL METHODS W.W.KUBIAK - ADVANCED ANALYTICAL METHODS

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ULTRAFILTRATIONProccess in which solution under high pressure permatethrough the membrane. Depending on size of membranepores the solvent molecules and small ions permatethrough the membrane, whereas particles, colloids andlarge molecules remain on the membrane. In ultrafiltrationthe pores diameters are 0.2 - 0.45 µm and the appliedpressure is 10 - 30 MPa.


Membrane and seperated latex particles


DIALYSISRemoval of small ions and particles from colloidal solutionsby semipermable membrane. Proccess is much faster whenelectrical field is applied (electrodialysis).


ELECTROPHORESISCharged colloidal particles migrate in electric field. Velocity ofmigration depends on charge, magnitude and shape of theparticles. It allows to separate different particles.Electrophoresis is performed on substrates such as celluloseacetate, agarose, polyacrylic gels etc. If capillaryelectrophoresis is used there is possibility to separate ions.


Apparatus for electrophoresisElectrophoresis of peptides from several animal meats


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aam-wyk2 [tryb zgodności]galaxy.agh.edu.pl/~kca/aam-sem-nas.pdf · Mixed substances may be separate if they differ at least in one physicochemical property. Basic of separation Method