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Journal of Chromatography A, 1180 (2008) 122130

Organotin speciation in French brandies and wines bysolid-phase microextraction and gas

chromatographyPulsed flame photometric detection

Julien Heroult , Mate Bueno,Martine Potin-Gautier, Gaetane Lespes

Laboratoire de Chimie Analytique Bio Inorganique et Environnement, UMR 5254,

Universite de Pau et des Pays de lAdour, B.P. 1155, 64013 PAU Cedex, France

Received 18 July 2007; received in revised form 16 October 2007; accepted 27 November 2007

Available online 4 December 2007

Abstract

An analytical method devoted to organotin compounds (OTC) determination in brandy and wine was developed. It is based on solid-phase

microextraction (SPME) of ethylated organotins. The following operating factors were examined: SPME mode/nature of fibre coating, sample

volume/dilution, and sampling time. The optimisation work led to dilute the sample in an aqueous buffer (1/11, v/v ratio) in order to satisfactorily

decrease the matrix effects due to competitive sorption of non-OTC species onto/into fibre coating. The optimised operating conditions consist of

polydimethylsiloxane (PDMS) coated fibre used in headspace mode for 30 min. In wines, the limits of detection (LOD) and quantification (LOQ)

ranged from 1 to 40 and 3 to 80 ng(Sn) L1 respectively, according to the species. The analytical validation was made by evaluating the accuracy of

OTC determination in spiked samples with various concentrations over the whole calibration range, i.e. from LOQ to 1000 ng(Sn) L1. Recovery

was around 80110% and precision (relative standard deviation, RSD) was between 12% and 25%. Despite the presence of two chromatographic

peaks corresponding to sulphur compounds during brandy analysis, the selectivity of the method is adequate. The analysis confirmed the analytical

performances and applicability of the method to wine and brandy samples. The obtained results emphasise the contamination of brandy and wine

by organotins, the storage in plastic container seeming to be confirmed as the main OTC source. 2007 Elsevier B.V. All rights reserved.

Keywords: Organotin; Wine; Brandy; Solid-phase microextraction

1. Introduction

Organotin compounds (OTC) are widely used in a lot

of human activities in agriculture and industrial processes.

Tributyl- (TBT) and triphenyltin (TPhT) are employed as wood

preservers or pesticides. Mono- and dibutyl- (MBT and DBT),

mono- and dioctyltins (MOcT and DOcT) are applied as cat-

alysts and stabilisers in plastic [poly(vinyl chloride) (PVC)]

production. According to grape culture and wine-making, OTC

can also be present in brandy and wine. In previous studies,

these species were detected in various wines, with concentra-

tions varying between 50 and 80,000 ng(Sn) L1 [16]. The

extremely high concentrations in some Canadian wines were

Corresponding author.

E-mail address: [email protected](J. Heroult).

attributed to the storage in PVC flasks [7]. Other authors did

not find differences in butyltin concentrations in wines stored

in plastic and glass bottles [5]. In most of the analysed sam-

ples, MBT and DBT were determined in concentrations ranging

from 100 to 500 ng(Sn)L1. There is no information available

on simultaneous determination of butyl-, phenyl- and octyltins,

and no data about phenyltin speciation in wines and brandies.

Because of the high OTC toxicity at very low concentrations,

sensitive and selective analytical procedures are required. Ana-

lytical development devoted to OTC has given rise to a great

deal of interest, especially in environmental samples. Studies

about OTC speciation in manufactured foodstuffs such as oils,

fruit juices or alcoholic drinks remain relatively limited, despite

quality control of food and drink [2,48]. However, analytical

request is increasing in more and more food and agrochemi-

cal industries. Consequently, constant analytical improvements

are required in order to have methods able to answer to the

0021-9673/$ see front matter 2007 Elsevier B.V. All rights reserved.

doi:10.1016/j.chroma.2007.11.084
mailto:[email protected]://localhost/var/www/apps/conversion/tmp/scratch_5/dx.doi.org/10.1016/j.chroma.2007.11.084http://localhost/var/www/apps/conversion/tmp/scratch_5/dx.doi.org/10.1016/j.chroma.2007.11.084mailto:[email protected]


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J. Heroult et al. / J. Chromatogr. A 1180 (2008) 122130 123

need and regulation. It is especially urgent since the interna-

tional institution dealing with food safety and normalisation

is working to define specific regulation dedicated to OTC in

manufactured media. The most recent analytical methods pro-

posed for organotin determination in wines concern butyltins

[5,8]. They were based on derivatisation andeither liquidliquid

extraction (LLE) in hexane or headspace solid-phase microex-

traction (HS-SPME), before gas chromatography (GC) with

flame photometric detection (FPD) or mass spectrometry (MS)

[5,8]. In HS-SPME, a 100m-polydimethylsiloxane (PDMS)

coated fibre was used. The derivatisation step was achieved by

hybridization with potassium tetrahydroborate (KBH4), Grig-

nard propylation or ethylation with sodium tetraethylborate

(NaBEt4). LLE led to too high limits of detection (LODs), over

300 ng(Sn) L1. By using HS-SPME, the LOD reported were

16200, 22100 and 1550ng(Sn)L1, respectively for MBT,

DBT and TBT. Although HS-SPME was used, strong matrix

effects were observed, mainly leading to important variation of

extraction yield. Thus, the LODs could be increased five times

according to the type of wine, e.g. from 20 to 100 ng(Sn) L

1

for DBT [8]. Other work dealing with volatile sulphur com-

pounds analysis in beer related matrix effects observed in

alcoholic drinks and induced by the presence of ethanol [9].

Two hypotheses were given to explain the effect of ethanol on

organic and sulphur compounds analysis: ethanol could either

act as co-solvent where analytes remained preferentially or

be responsible for sorption competition onto/into fibre coat-

ing.

Given the different projects concerning OTC regulation in a

wide range of media, the general aim of the present work is to

investigate an analytical procedure able to reach organotin spe-

ciation in manufactured solutions with complex content, quitedifferent from environmental media. The challenge rests on the

understanding of HS-SPME step, with regard to the presence of

matrix components sufficiently volatile to be co-extracted. The

acquired information is especially useful to complete theknowl-

edge about theSPME fibre coating behaviour. More specifically,

the study focuses on the optimisation of a method for simulta-

neous determination of butyl-, octyl- and phenyltins in routine

conditions. The media chosen were various types of wine and

brandy. The OTC traceability required a particular attention

regarding the sensitivity and robustness of the method. The

reduction of matrix effects due to co-extracted volatile com-

pounds was investigated.The analyticaldevelopment was based

on SPME GC-pulsed flame photometric detection (PFPD), pre-viously demonstratedas suitable for OTC speciation in complex

environmental matrices [1015].

2. Experimental

2.1. Instrumentation

A Varian 1079split/splitless temperature programmable

injector (Walnut Creek, USA) associated to a Varian 3800

gas chromatograph coupled with a pulsed flame photomet-

ric detector was used. The GC system was equipped with

a 30 m

0.32mm capillary column (film thickness 0.25m)

coated with (5% phenyl)methylpolysiloxane, 007-5 (Quadrex,

New Heaven, CT, USA). The operating conditions were

optimised previously in our laboratory [15]. The following tem-

perature program was applied for the separation of OTC: the

column temperature was held at 80 C for the first minute,

raised to 125 C at a heating rate of 20 Cmin1, to 190 C

at 5 Cmin1, to 225 C at 10 Cmin1, then to 270 at

30 Cmin1 and held at the final temperature for 3 min. The

splitless injector port was kept at 250 C and the temperature of

the detector was 350 C. Nitrogen was used as the carrier gas

(2mLmin1).

The detector operating conditions have been precisely

described elsewhere [12]. The signal corresponds to the emis-

sion of the Sn H molecular bond and was measured via a high

transmission band filter (> 610 nm; OG590, Schott, France).

According to the tin emission profile, signalacquisition was car-

ried out with a gate delay of 3.0 ms and a gate width of 2.0ms

after each flame ignition.

The investigation about co-extracted matrix componentswas

performed by using a Hewlett-Packard 6890 GCMS system(Palo Alto, CA, USA). The GC system was equipped with

a capillary column HP-5 (30m 0.32mm I.D.) coated with

(5% phenyl)methylpolysiloxane (film thickness 0.25m) (Agi-

lent Technology, Massy, France). Ultrapure helium was used as

carried gas, with a flow rate of 1.7 mL min1. The mass spec-

trometer was operated with electron impact (EI) at 70 eV as

ionisation potential, in positive ion mode. The injector temper-

ature was kept constant at 250 C. The transfer line was held at

280 C. Mass range from m/z 19500 was recorded in full scan

mode.

The manualSPME device was obtained from Supelco (Belle-

fonte, PA, USA). The fibres used were coated with either100m polydimethylsiloxane (PDMS) or 75m carboxen-

polydimethylsiloxane (CAR-PDMS) phases. These two types

of fibres were previously found to give satisfactory results for

OTC extraction [10,13].

Mechanical shaking during the SPME procedure was per-

formed using an elliptical table (KS 2502 basic) from Prolabo

(Fontenay Sous Bois, France). The maximum adjustable shak-

ing speed corresponded to 420 rpm. This shaking mode was

previously found to be the most efficient [11].

2.2. Standards and reagents

Monobutyltin trichloride (MBT, 95%), monophenyltintrichloride (MPhT, 98%) and diphenyltin dichloride (DPhT,

96%) were purchased from Aldrich (Milwaukee, WI, USA).

Dibutyltin dichloride (DBT, 97%), tributyltin chloride (TBT,

96%), triphenyltin chloride (TPhT, 95%) and tripropyltin chlo-

ride (TPrT, 98%) were obtained from Merck (Darmstadt,

Germany). Monooctyltin trichloride (MOcT, 97%), dioctyltin

dichloride (DOcT, 97%) and trioctyltin chloride (TOcT, 97%)

came from Lancaster (Strasbourg, France). Organotin standard

stock solutions (1000mg(Sn)L1) were prepared in methanol.

Working standard solutions (10 mg(Sn)L1) were prepared

weekly from stock standard solutions by dilution in Milli-Q

water (18.2M

) (Millipore, Bedford, MA, USA). Standard


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124 J. Heroult et al. / J. Chromatogr. A 1180 (2008) 122130

solutions of 100g(Sn) L1 were daily prepared. All the stan-

dards were stored in the dark at 4 C.

Ethanoic acid, ammoniac and nitric acid were obtained from

J.T. Baker (Paris, France). Methanol was purchased from Pro-

labo. Sodium tetraethylborate (NaBEt4) was purchased from

Galab products (Geesthacht, Germany). NaBEt4 was dissolved

in Milli-Q water to provide a 2% (m/v) ethylating solution.Glassware was decontaminated overnight in 10% (v/v) nitric

acid solution and rinsed with Milli-Q water.

2.3. Samples

Various brandies, white and red wines from west, south-west

and south of France were analysed. They were chosen on the

basis of different sample matrices, according to their production

process and storage. Three types of brandy were studied: (1) a

pure wine distillation product, directly put into glass flask after

distillation, (2) a brandy let soaked with oak shavings and (3)

a brandy corresponding to a distillation product stored in oak

barrel for two years. The brandy alcohol percentage (AP) was40%. Sweet white wines were originating from two different

wines (AOC type) and glass-bottled. Their AP were 12.5% and

17%, respectively. White and Red table wines (blended; 11%

AP), stored in plastic bottles were also analysed.

For analytical development and optimisation, an OTC-free

brandy sample was used. It was chosen because of its high alco-

holic degree and the most important matrix effects observed

during preliminary tests. It was spiked with the eight OTC of

interest, i.e. butyl-, phenyl- and octyltins. It is called brandy-test

sample later on.

2.4. Analytical procedure

An aliquot of brandy or wine sample of varying vol-

ume (540 mL) was directly introduced into a derivatisation

reactor. Ethylation was carried out using NaBEt4 solution

(0.5 mL, preliminary tested and validated volume) in a sodium

ethanoateethanoic acid buffer (0.2 mol L1, pH 4.8, volume

varying from 20 to 80 mL) [13]. For SPME extraction, both

direct and headspace (HS) sampling modes were used in a pre-

liminary study. In direct mode, the fibre was immersed in the

sample/buffer mixture immediately after NaBEt4 addition, for

30min [11]. For HS sampling, the SPME fibre was inserted in

theheadspace10 minafterNaBEt4 addition,stirring timeneeded

to equilibrate liquid and gaseous phase analyte content as pre-viously studied [13]. HS-SPME sampling was then performed

undermechanicalstirring.Differentextraction timeswere tested

and results have been presented later on.

After SPME sampling, the fibre was introduced into the GC

injector port where the analytes were thermally desorbed for

1 min. The same procedure, with exception that no sample was

added, was applied to determine blanks. All the analyses were

made in duplicate at room temperature (22 2 C).

Quantification of OTC was performed by applying the

standardadditioncalibration method usingTPrT as internalstan-

dard. OTC standards were added into the reactor just before

NaBEt4 addition.

2.5. Chemometrics

Simultaneous optimisation of operating factors was per-

formed by using experimental design. This approach allows the

data to be modelled and transformed into continuous informa-

tion on the whole experimental field [16]. 3NF design(whereNF

represents the number of studied factors) was chosen because

it is easy to use and sufficiently robust. Three different levels

of adjustment, respectively noted 1, 0 and +1 were used for

each factor (X), involving N= 3NF experiments. This type of

design also offers a sequential approach, i.e. the possibility to

extend the experimental field during the optimisation. This is

due to the regular distribution of the experiments in the stud-

ied field. The standard deviation (s) of the measured responses

(Y) was estimated by duplicating each experiment [17]. The

effect (A) of a factor or an interaction between two factors on

a response was calculated by using the least-squares method.

Correspondingerror(dA) was calculated byusing themean stan-

dard deviation (s) of the response [17]. The effect was regarded

as significant if it was higher than the precision. The modellingrelied on a second-order polynomial fitting on the variation of

the response as a function of the significant factors (Y=AX).

It was validated by evaluating the precision (via the determi-

nation coefficient, R2), the signification and lack-of-bias (by

FisherSnedecor statistics, F-tests respectively noted Fsign and

Fbias) [17]. All statistical tests and uncertainty calculations were

made in a confidence level of 95%. Mathematical and statisti-

cal calculationswere performed by using NEMRODW (2000-D

version from LPRAI, Marseille, France) and EXCEL software.

3. Results and discussion

3.1. SPME optimisation

In this part, brandy aliquots were spiked with the different

organotins with concentrations adapted to the chromatographic

responses of the analytes. Extracted amounts (and so extraction

efficiency) were evaluated by considering the peak areas [11].

3.1.1. SPME mode and fibre coating

Direct and headspace sampling modes were first compared

by using PDMS fibre, as this coating was previously shown to be

well-adapted to simultaneous extraction of butyl-, phenyl- and

octyltins from aqueous samples [11,14,15]. HS-SPME should

allow competitive co-extraction of low-volatile non-organotinspecies into the fibre to be reduced, and has experimentally

shown the best analytical performances, especially if several

organotins (including butyl- to octyltins) have to be analysed

[9,13]. According to Fig. 1, HS-SPME from the brandy-test

sample actually provides higher peak areas in comparison with

direct extraction. This mode was thus selected for further devel-

opment. Because of the particular nature of the sample matrix,

thenatureof fibre coating was also tested, especially with regard

to the co-extraction of non-organotin species currently found in

alcoholic drink. In the literature, both PDMS and CAR-PDMS

fibres were used for the analyses of volatile organic and sulphur

compounds in different beverages such as beer or fruit juices


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Fig. 1. Typical GCPFPD chromatograms according to SPME mode. Other

operating conditions: Direct SPME: 30 min sampling, 20mL sample volume;

Head Space SPME: 15 min sampling, 20mL sample volume. Spiked sample:

from 100 (MBT) to 2000 (TPhT) g(Sn)L1.

[9,18,19]. From a previous study concerning aqueous samples,

PDMS coating allowed higher quantitative simultaneous extrac-

tion of butyl-, octyl-, MPhT and DPhT, whereas CAR-PDMS

was showed to be well-adapted to the most volatile methyltins

[13]. TPhT was also more efficiently extracted by using this

fibre than with PDMS. A comparison of both fibre coatings in

HS sampling mode for the brandy-test sample has been carried

out. Results showed that PDMS coating gave higher OTC peaks

than the ones obtained with CAR-PDMS fibre (up to 20 times

higher), which is inagreementwith ourprevious results obtained

in water samples [13]. Consequently, PDMS fibre was selectedin the analytical procedure.

3.1.2. Operating factors

3.1.2.1. Preliminary experiments. In HS-SPME, the mass

transfer at fibre/headspace and headspace/solution interfaces

directly determines the amounts of analytes extracted by the

SPME coating [20,21]. These extracted amounts depend on the

analyte concentrations and volumes of the three phases. The

main limiting parameter in HS-SPME is the transport of the

analytes from the solution to the headspace. It can be enhanced

by an efficient shaking of thesolution, which insures continuous

renewal of OTC at the solution surface [22].The matrix effects induced by the presence of ethanol and

other organic volatile compounds forming aroma were first con-

sidered. GCPFPD and GCMS analyses of a brandy sample

and an ethanol/water mixture with the same ethanol content

(40%) were made, each one being diluted in ethanoic buffer

and OTC spiked. The results are presented in Fig. 2. An

important decrease of peak areas can be observed from the

brandy sample. According to the corresponding GCMS chro-

matograms,different non-OTCvolatilecomponentsaredetected

in this sample. Indeed, organic volatile compounds frequently

present in alcoholic beverages such as fatty acids (octanoic,

decanoic, dodecanoic acids) and brandy aromas (vitispirane

Fig. 2. Compared GCPFPD and GCMS chromatograms from (a) an

ethanol/water mixture (40/60, v/v), (b and c) a diluted brandy sample, with

respectively (5/55, v/v) and (20/40, v/v) dilution. OTC concentration in solution

(sample+ buffer): from 167 (MBT) to 1667 (TPhT) ng(Sn)L1 for GC-PFPD

analysis and from 1.67 (MBT) to 16.7 (TPhT) g(Sn)L1 for GCMS anal-

ysis. MS Identification: 1. ethanol, 2. octanoic acid, 3. vitispirane, 4. 1,2

dihydro-1,1,6-trimethylnaphtalene (TDN),5. decanoic acid,6. dodecanoic acid,

7. silicate compounds.

and1,2 dihydro-1,1,6-trimethylnaphtalene [TDN]) areextracted

in high quantity, simultaneously to OTC. This co-extraction

induces the OTC sorption onto the SPME fibre to be widely

decreased [19,23]. These results highlight that ethanol is not

the only responsible factor for the observed matrix effects. In

order to decrease these matrix effects, Azehna and Vasconce-

los proposed a sample pre-treatment based on a preliminary

extraction of OTC from wine matrix by an aqueous solution

of tetramethyl ammonium hydroxide (TMAH) [8]. However,

this pre-treatment had no significant effect and was rather time-

consuming (50 min). In the present study, other pre-treatments

were tested in order to remove co-extracted volatile species:


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Fig. 3. Influence of solution volume (sample+ buffer) on extraction effi-

ciency. Volumes (mL): headspace/[sample + buffer]: (a) 60/[20 + 40] and (b)

120/[40+ 80]. Spiked sample: from 100 (MBT) to 2000 (TPhT)g(Sn)L1.

heating (30 C) nitrogen degassing (for 3075min), vacuum

degassing (5 min), ultrasonic bath (10 min), headspace vacuum

extraction (2 min). Results obtained showed more or less impor-

tant OTCpeak area decrease,whichis probably theconsequence

of OTC losses during pre-treatments. Dilution of the sample in

buffer was also tested. Because a significant improvement ofthe OTC peak areas was obtained, further investigations were

performed and are presented later on.

The effect of solution volume (i.e. brandy-

test sample + buffer) was also tested using a fixed

headspace/[sample + buffer] ratio (1/1, v/v) in reactors

with same geometry but different total volumes, respectively

120 and 240 mL. The positive effect of 120mL reactors on

the HS-SPME efficiency is obvious for all organotins, as

illustrated in Fig. 3. The use of smaller reactors leads to not

less than a two-fold increase of OTC peak areas in comparison

with 240 mL reactors. Such observation may be explained by

different stirring efficiencies due to different solution volumesto be agitated as a function of reactor volume. In the present

conditions (mechanical stirring at 420rpm), a solution volume

of 60 mL in 120 mL reactor appears as the most convenient.

3.1.2.2. Experimental design. According to the description of

the analytical process (see Section 2.4.), literature and pre-

liminary tests, the following three factors were taken into

consideration in their respective experimental field (i.e., and

+ levels, respectively):

(1) headspace/solution [i.e, sample+ buffer] volume ratio

(HS/S) studied at 1/1 (60 mL/60 mL) and 1/2 (40 mL/

80 mL);

(2) sample/aqueous buffer volume ratio (S/B), first considered

between 1/2 (20 mL/40 mL for 60 mL total volume of solu-

tion and 27mL/53mL for 80 mL total volume of solution)

and 2/1 (40 mL/20 mL for 60 mL and 53 mL/27 mL for

80 mL);

(3) extraction time: theexperimental field of this factorwas pre-

liminary studied between 5 and 45 min. As no significant

response improvement was observed over 30 min, experi-

mental field was then considered between 5 and 30 min.

Because of operating constraints and in order to avoid a too

high number of experiments, the experimentation wasorganised

in two 32 designs, each one corresponding to the low and high

levels of factor (1) (i.e. 60 or 80 mL of solution). Consequently,

each design addressed the two factors (2) and (3).

The organotin chromatographic peak areas were considered

individuallyas theresponsesto optimise.Experimental setswere

performed with constant OTC amount [5 ng(Sn) for MBT to

100 ng(Sn) for TPhT] in the reactor in order to evaluate the

actual extracted OTC amount considering the matrix effects.Some selected HS-SPME time profiles of the eight analytes

are presented in Fig. 4. They were obtained from the mod-

elling according to the approach described in chemometrics

part (model validation: R2 > 0.86, Fsign > 115 and Fbias < 5). In

order to compare them, scale was kept similar between some

of these figures. Because of the simultaneous ethylation/HS-

SPME, extracted amounts are dependent on both ethylation and

extraction yields, but time profiles are mainly dependent on

extraction efficiency as no limitation is supposed to occur from

ethylation step (no kinetic limitation and NaBEt4 in excess).

Individual profiles present significant differences according to

the degree of substitution and nature of the organic groupbonded to tin atom. Concerning mono- and disubtituted species,

equilibrium generally appears to be reached after 1520 or

2030 min, according to volume ratios. For trisubtituted com-

pounds, extracted amounts show a continuous weak increase in

the whole sampling time range.

In the octyltin series, mono- and disubtituted species appear

quantitatively extracted whatever be the experimental condi-

tions. This may be due to their lower volatility with regard to the

other organotins, leading to lowest extracted amounts. For the

two other organotin series, i.e. butyl- and phenyl-, the extracted

amount generally decreases from mono- to tri-substituted tin.

The most important dilution of the sample (S/B = 1/2) promotes

the HS-SPME of mono- and disubstituted species. According tothis observation, the sample/aqueous buffer volume ratio was

then studied down to 1/11 (i.e. 5/55, v/v ratio). The results

obtained in this extended experimental field (see Fig. 5) confirm

that the OTC extraction efficiency is greater for higher dilution,

especially when sample/buffer volume ratio is below 1/5. Sev-

eral hypotheses can be made to explain these observations. On

the one hand, as the solubility of organotins in the liquid phase

varies according to their substitution degree, the liquid phase

composition (mainly based on ethanol/water ratio) could lead to

differences in species partitioning between headspace and solu-

tion phases and then, differences in extraction yields. However,

from preliminary experiments, similar extraction yields were


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Fig. 4. Organotin HS-SPME timeprofiles plotted accordingto experimentaldesign modelling: (A) butyltins, (B) phenyltins, (C) octyltins. Solution= sample + buffer.

Headspace/solution volume ratios (HS/S): (1/1): Solution volume= 60 mL; (1/2): Solution volume = 80 mL. Sample/buffer volume ratios (S/B): (1/2): 20mL/40mL

(for 60mL solution) or 27mL/53 mL (for 80 mL solution); (2/1): 40mL/20 mL (for 60 mL solution) or 53mL/27mL (for 80 mL solution).

obtained from HS-SPME sampling in water and ethanol/water

mixture (40/60, v/v). On the other hand, discrimination between

OTC according to their volatility could occur. This phenomenon

has been already observed when OTC were extracted by HS-

SPME from aqueous samples [13,14]. Moreover, in the present

case, importantsorption competitionsalso existbetween thedif-

ferentvolatilematrix components, as highlighted in Fig. 2. They

even could lead to desorption of the most volatile OTC when the

alcoholic matrix is not sufficiently diluted (as seen for S/B = 2/1,

on Fig. 4, curves in grey lines). Sorption competition between

non-OTC and OTC compounds could also explain the signifi-

cant positive effect of the matrix dilution clearly emphasised in

Fig. 5. Finally, as shown in Fig. 2b andc, silicate compoundsare

detected with a 20/40 (v/v) dilution, whereas they are not with a

1/11 S/B ratio. These compoundsprobably come from reactions

between fibre bulk (containing silicon) and matrix organic com-

pounds. It could explain the rapid fibre degradation observed

during experiments when the sample is not sufficiently diluted.

Thus, dilution of the sample in aqueous buffer allows lower

matrix effects and protects fibre against a too early degradation.

The headspace/solution volume ratio was also found to have

a significant effect on extraction efficiency, HS/S= 1/1 (corre-

sponding to 60 mL solution in a 120 mL reactor see Fig. 4)

giving the highest extraction yield especially for MBT, DBT,


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Table 1

Analytical performances in brandy

LOD (ng (Sn) L1) LOQ (ng (Sn) L1) Sensitivity (mVng(Sn)1) [*RSD] **R2 Recovery (%) [*RSD]

MBT 3.4 8 5.6 0.1 [1.8] 0.9933 104 19 [18]

DBT 1.6 4 1.76 0.01 [0.5] 0.9993 96 6 [6]

TBT 4.6 11 0.70 0.01 [1.4] 0.9952 98 23 [23]

MPhT 17 40 3.21 0.07 [2.2] 0.9973 107 10 [9]

DPhT 30 71 0.065 0.001 [1.5] 0.9954 109 10 [9]MOcT 52 123 0.103 0.001 [1.0] 0.9968 93 10 [11]

*RSD: relative standard deviation; **R2: determination coefficient.

MPhT andDPhT. This ratio does notcorrespond to theminimum

headspace volume, although a minimum HS was expected to

give an optimal extraction [9,13]. This result is probably related

to the stirring efficiency as already noticed [11] and/or matrix

effects induced by higher amounts of non-OTC volatile com-

ponents as discussed just before. As a consequence, a strong

interaction between HS/S and S/B ratios occurs, as clearly

enhanced for octyltins (see Fig. 4). It is in agreement with thepreliminary results presented before in this paper.

With regard to the influence of the different studied fac-

tors, the optimised operating conditions were the following: (1)

30 min extraction time; (2) 1/11sample/buffer volume ratio (i.e.

5 mLofsample+55 mLof buffer)and (3)1/1 headspace/solution

volume ratio (i.e. 60 mL [sample + buffer] in a 120mL reactor).

3.2. Analytical performances

Thelimitsof detection(LOD) andquantification (LOQ) were

calculated by using the calibration curve method [24,25]. The

method accuracy (i.e. trueness and precision defined according

toISO [26]) wasalsodetermined. Precisionwas evaluated by the

relative standard deviation (RSD) of the calibration slope (i.e.

sensitivity) and the determination coefficient. Trueness was esti-

mated via themean recoveryobtained by determining OTC with

concentrations covering the calibration curve in spiked samples.

The results for brandy and wine samples are summarised in

Tables 1 and 2 respectively.

The butyltin LOD are 310 times lower than those reported

in the literature of wine [5,8]. The detection limits for MPhT,

DPhT andMOcTaresatisfactory, eveninbrandywiththehighest

alcohol content. TPhT andDOcT canalso be detected.However,

due to their lower volatility, their LOD remain very high, over

1000 ng(Sn)L1.

Accordingto thedatapresentedin Tables1and2 andthesatis-

factory recovery (trueness and precision), the optimised methodappears suitable for wine and brandy analysis.

3.3. Analysis of wine and brandy samples

Analyses were performed in routine conditions. Some sam-

ples of brandy originally stored in oak barrel during maturing

were analysed. They appeared slightly contaminated by MBT

only. Concentrations ranged between 10 and 50 ng(Sn)L1.

The analytical precision was around 37%. Some non-OTC

species were also detected by PFPD, as shown in Fig. 6. These

compounds were observed in brandy only. They involved chro-

matographic peaks withthe typical shapeof sulphur compounds.

Bravo et al. studied sulphur interferences and identified them

from their retention times [14]. According to this study and

the retention times measured from Fig. 6, the first peak could

be possibly attributed to diethyl trisulphur (*IS1: Et2S3) and

the second one to diethyl tetrasulphur (*IS2: Et2S4). They

could correspond to species formed during ethylation, as pre-

viously demonstrated [14]. Unfortunately, these species could

Table 2

Analytical performances in white (in white) and red (in grey) wines

LOD (ng (Sn) L1) LOQ (ng (Sn) L1) Sensitivity (mVng(Sn)1) [*RSD] **R2 Recovery (%) [*RSD]

MBT 2.2 5.2 44.0 0.3 [0.7] 0.9949 111 18 [16]

2.5 5.7 44 1 [2.3] 0.9920 123 22 [18]

DBT 1.2 2.9 61.2 0.7 [1.1] 0.9956 96 12 [12]

1.7 3.9 92 2 [2.2] 0.9922 120 17 [14]

TBT 1.6 3.9 18.7 0.3 [1.6] 0.9943 105 16 [15]

2.1 5.3 34 1 [2.9] 0.9911 94 10 [11]

MPhT 2.2 5.2 5.77 0.09 [1.6] 0.9949 114 29 [25]

9.1 20 32 1 [3.1] 0.9884 81 10 [12]

DPhT 18 43 2.67 0.03 [1.1] 0.9944 79 15 [19]

37 82 4.9 0.2 [4.1] 0.9915 90 11 [12]

MOcT 30 71 6.5 0.1 [1.5] 0.9920 104 23 [22]

35 69 13 1 [7.7] 0.9723 108 17 [16]

*RSD: relative standard deviation; **R2

: determination coefficient.


8/9


Fig. 5. Organotin extraction profiles according to sample/buffer volume ratio

Extraction duration, 30 min; total volume, 60mL.

Fig. 6. Chromatogram of a brandy sample exhibiting non-OTC species (*IS1

and *IS2).

not be identified from the GCMS chromatograms due to the

lack of MS sensitivity. Finally, because of the efficient chro-

matographic separation of sulphur species and organotins, the

OTC quantification was not disturbed by these compounds and

these first applications confirm the suitability of the analytical

method.

TheTable3 presents theresults obtainedon selectedbrandies,

white and red wines. MBT was found in all samples, whereas

DPhT was never detected. In most of the samples, the OTC

concentrations are lower than 150ng(Sn) L1, some of them

being close to LOQ. The precision of the determination remains

satisfactory for all the different analysed matrices.

Considering the brandy samples, the most contaminated

appears to be the one stored with oak shavings. The three

butyltins were found, showing that wood treatment may con-

tribute to the contamination. However, TBT and DBT do not

Table 3

Organotin speciation in various brandies and wines

Sample Characteristics (alcohol content) Concentrations (ng(Sn)L1)

MBT DBT TBT MPhT DPhT MOcT

Brandy 1 distillation product stored in glass (40%) 27 2 nd nd


9/9


seem very persistent, being not detected in brandy stored for

several years in oak barrel. Other sources of OTC contamina-

tion exist since MBT was also found in the distillation product

and MOcT was present in brandy samples (see Table 3). The

occurrence of this last compound is usually attributed to plas-

tic material. The brandy storage in plastic tank could explain

the presence of this compound. The AOC sweet white wines

appear slightly contaminated. The highest OTC concentrations

were found in table wines stored in plastic bottles that led to

significant MBT and DBT content. These results are in agree-

ment with those reported in literature [5,8]. They confirm the

impact of storage in plastic container. An important MPhT con-

centration was found in the white wine sample. MPhT presence

in such concentration remains difficult to explain. It could corre-

spond to an accidental contamination or could come from TPhT

degradation, TPhT being usually used as agricultural biocide in

continental media.

4. Conclusion

In the field of manufactured solutions, wine and brandy are

at once complex matrices and very good supports to evalu-

ate SPME fibre coating behaviour. However, analytical studies

devoted to this kind of matrices remain scarce in the literature.

Onemajor difficulty comes from aromasandflavours formedby

numerous volatile compounds. According to the OTC analytical

process, these species are co-extracted into the SPME fibre con-

currently with ethylated OTC.This phenomenon leads to drastic

decrease of analyte chromatographic signals, poor repeatability

and insufficient sensitivity.

In the present study, a rapid method for simultaneous deter-

mination of butyltins, MPhT, DPhT and MOcT without anypretreament was optimised and validated. The matrix effects

were simplyovercomeby diluting thesample. With regardto the

analytical performances, this method appears robust and precise

with RSD generally around 1020% over a range of calibration

from LOD up to 1000ng(Sn)L1. The results obtained from

brandy and wine analysis show the applicability and suitability

of the developed method in routine conditions. The presence

of butyl-, phenyl- and octyltins in various concentrations in

these samples emphasises the interest of analytical develop-

ments adapted to speciation of all these OTC. TPhT and DOcT

can not be quantified at satisfactory level and further investi-

gation is needed to overcome this difficulty. Finally, the results

obtained open new perspectives in the SPME-based analysis of

manufacturedmedia, which is especially importantaccording to

the increasing need of adapted analytical procedures and future

regulations.

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