Abstract An analytical method is described for assess-ing the vapour concentration of 11 pesticides (bioallethrin,chlorpyriphos methyl, folpet, malathion, procymidone, quin-tozene, chlorothalonil, fonofos, penconazole and trimetha-carb) in confined atmospheres (e.g. a greenhouse afterpesticide application). This study is a successful extensionof a method previously developed by the authors for di-chlorvos to much less volatile pesticides. Sampling wasperformed by using polydimethylsiloxane–solid phasemicro-extraction (PDMS–SPME) fibres immersed in a250-mL sampling flask through which air samples weredynamically pumped from the analysed atmosphere. Aftera 40-min sampling duration, samples were analysed byGC/MS.

Calibration was performed from a vapour-saturated airsample. The linearity of the observed signal versus pesti-cide concentration in the vapour phase was proved fromspiked liquid samples whose headspace concentrationswere measured by using the proposed method. This pro-cedure gave calibration curves with regression coeffi-cients (R2) greater than 0.98, and the repeatability of thesemeasurements was found with RSDs of 1.9–7.6%. As afield application test, this analysis procedure was used forthe determination of gaseous procymidone concentrationsas a function of time in the atmosphere of an experimen-tal 8-m2 and 20-m3 greenhouse. The pesticide was sprayedaccording to real cultivation conditions, and measure-ments were made for 80 h after application (8 measure-ments). The observed concentrations found ranged from200 to 500 µg m–3, thus indicating the level of contamina-

tion of the air breathed by people in such working condi-tions.

Keywords Pesticide vapours · SPME/GC/MS analysis ·Air sampling · Greenhouse atmospheres

Abbreviations GC/MS gas chromatography/mass spectrometry · SIM selective ion monitoring · FC43 perfluorotributylamine · RSD relative standard deviation · LOD limit of detection · LOQ limit of quantification

Introduction

Recent studies indicate that pesticide contamination issystematically invading all the segments of our biosphere[1]. This can be considered as a consequence of the evo-lution of human activities in our modern societies.

The atmosphere is well known to be a good pathway forthe dissemination of pesticides [2, 3] sometimes in zonesfar away from their emission sites (e.g. in remote Antarc-tic areas [4] or high-altitude mountain Lakes [5]). Actu-ally, some papers dealing with the characterisation of at-mospheric contamination by pesticides are now available.Different methods are used to evaluate the contaminationof the atmosphere by pesticides and to describe processesby which these compounds are transferred into the atmo-sphere (e.g. vaporisation, spraydrift etc.) [4, 6, 7, 8, 9].Nevertheless, measuring low levels of contaminant con-centrations in air samples is still a real challenge for ana-lytical chemists today [9, 10, 11]. Usual sampling consistsof collecting high volumes of contaminated air that are fil-tered through an adapted solid-phase material or washedout with organic solvents. In a further processing step, an-alytes have to be desorbed and/or concentrated before be-ing chromatographied [12], and this additional work upconsiderably increases duration and cost of the totalanalysis. Obtained data therefore give averaged valuescorresponding to extended sampling times (of at least sev-eral hours) and are recommended in the case of studies in

Federico Ferrari · Astrid Sanusi · Maurice Millet ·Michel Montury

Multiresidue method using SPME for the determination of various pesticides with different volatility in confined atmospheres

Anal Bioanal Chem (2004) 379 : 476–483DOI 10.1007/s00216-004-2587-0

Received: 11 September 2003 / Revised: 19 February 2004 / Accepted: 5 March 2004 / Published online: 15 April 2004

ORIGINAL PAPER

F. Ferrari · A. Sanusi · M. Montury (✉)Equipe Périgourdine de Chimie Appliquée LPTC, Université Bordeaux 1/CNRS UMR 5472, BP 1043, 24001 Périgueux Cedex, FranceTel.: +33 (0) 5-53352429e-mail: m.montury@epca.u-bordeaux1.fr

M. MilletLaboratoire de Physico-Chimie de l’Atmosphère CGS, Université de Strasbourg I, CNRS UMR 7517, 1 rue Blessig, 67084 Strasbourg Cedex, France

© Springer-Verlag 2004

which time-weighted average methods (TWA) are used[13, 14]. In cases where the evolution of instant concen-trations is required, these types of measurement are notideal, and a real need exists for rapid methods able to af-ford more punctual measurements. The situation is differ-ent for pollution of confined atmospheres (e.g. green-house, stockroom etc.) where worker exposure to pesti-cides may be intensive during and after application [15,16] despite recent efforts [17, 18]. In confined atmo-spheres, there is also a need for relatively rapid samplingmethods in order to assess the real worker exposure risk[19]. As an example of the urgent need for such methods,the Common Acceptance Directive 91/414/EEC, which dealswith the authorisation of plant protection products (pesti-cides) and their controlled use, requires that regulatorsfrom EU member States evaluate levels of worker expo-sure to pesticides during their intended use as part of theauthorisation process.

For sampling purposes, the so called solid-phase micro-extraction method (SPME), developed by Pawliszyn andhis group [20], has proven to be particularly convenientfor the determination of traces of organic pollutants in en-vironmental samples. According to the thermodynamicallycontrolled principle of partitioning, organic analytes con-tained in the analysed matrix accumulate onto the poly-meric coating of a silica microfibre probe, which is di-rectly immersed in the aqueous sample. After an optimisedexposure time that can be even shorter than the full equili-bration time [21], the fibre is withdrawn and desorbed intothe injection port of the chromatographic system.

This innovative method has been applied for the analy-sis of many types of water contaminants [22, 23] and wasvery rapidly and extensively used for the analysis of pes-ticide traces in all kinds of environmental matrices includ-ing waters [24, 25], aqueous solutions and suspensions[26, 27] and fruits and vegetables [28, 29].

Very recently, the authors also demonstrated that dichlor-vos, a semi-volatile insecticide, was easily sampled bySPME from the confined atmosphere of a greenhouse andanalysed at the level of few µg m–3 by GC/MS [30].

The objective of this paper was to enlarge the applica-tion field of the aforementioned analysis method to 11other pesticides with much lower volatilities at room tem-perature. Thus, bioallethrin, chlorothalonil, chlorpyriphosmethyl, cyanofos, folpet, fonofos, malathion, pencona-zole, procymidone, quintozene and trimethacarb were se-lected for this study, since their saturated vapour pressuresranged from 10–1 to 10–5 times that of dichlorvos, and alsobecause they are intensively used to protect productsgrown in greenhouses. As a consequence, they can also bebreathed by workers in the course of their professional ac-tivities.

Experimental

Reagents

Standards of pure bioalletrin (94%), chlorpyriphos methyl (99.0%),folpet (99%), malathion (99.5%), procymidone (99.7%) and quin-

tozene (99.5%) were supplied by Dr. Ehrenstorfer GmbH, Augs-burg, Germany; chlorothalonil (98.5%), fonofos (98.0%), pencona-zole (99.3%) and trimethacarb (98.0%) were supplied by Riedel-deHaen AG, Seelze, Germany; cyanofos was supplied by Chem Ser-vice, West Chester, PA, USA. Each pure standard was stored at–18°C.

Instrumentation

All SPME fibres – polydimethylsiloxane (PDMS) 100 µm; polydi-methylsiloxane–divinyl benzene (PDMS–DVB) 65 µm; carboxen–polydimethylsiloxane (CN–PDMS) 75 µm and polyacrylate (PA)85 µm – were provided by Supelco (USA).

A ThermoFinnigan GC/MS coupling system (Polaris ion-trapMS and GC-Q 2000) was used for analysing samples that were di-rectly introduced into the GC injection port with the SPME mani-fold. The chromatographic column used was a DB-5MS (Supelco),30-m long with a 0.25-mm ID and a 0.25-µm thickness.

A locally commercially available aquarium-type electric pump(5 W, 2 L min–1) was used to generate a homogeneous gas fluxthrough the sampling system.

Application of procymidone to field samples was performed inan experimental 8-m2 and 20-m3 greenhouse. Pesticide treatmentswere applied onto strawberry cultivations according to usual pro-fessional procedures.

Sample preparation

All measurements were made by exposing the selected SPME fibreto air samples. According to the objectives of this study, three dif-ferent assemblies were used. In the first one, corresponding to lab-oratory condition experiments (Fig. 1), the 250-mL sampling flaskwas connected to a 2.5-L glass bottle by using 5-mm-ID stainlesssteel pipes and an aquarium-type pump. Liquid or solid samples ofpure pesticides were introduced into this bottle to obtain a vapour-saturated atmosphere that was regularly circulated throughout thewhole assembly and especially the sampling flask. Sampling wasperformed by immersing SPME fibres into the sampling flaskthrough a septum wrapped with an aluminium foil for a definedduration.

In the second assembly (Fig. 2), which was used for assessingthe linearity of the method in terms of obtained signals versus con-centrations of the analyte in the vapour phase, extractions were car-ried out in the headspace mode from 5-mL vials containing spikedsolutions of the pesticide mixture in water and equipped with aglass-coated stirring bar and a thermostatic bath. The choice of thisassembly is due to the difficulty in generating gas-phase calibra-

477

Fig. 1 Laboratory assembly used for SPME samplings of pesti-cides vapours

478

tion samples of defined concentration, especially for pesticidesthat have very low vapour pressures.

This approach is in accordance with the process model for thethree-phase system involved in headspace solid-phase microex-traction (HS–SPME) as described by Zhang and Pawliszyn [31].Fibres are used to extract only insignificant portions of the targetanalytes in a given phase (HS or liquid) without affecting their dis-tribution in the whole system. Based on external calibration, theycan give the analyte concentrations in the phase of interest. So,measurements performed in the HS from perfectly agitated spikedaqueous solutions are representative of the gradient of their initialconcentrations.

In a third assembly, which was used for greenhouse measure-ments, the sampling flask was only connected through the outputknob to the pump with a stainless pipe, and the input knob was justopen to the greenhouse atmosphere (Fig. 3).

According to most of the procedures described in the literaturein this field, all sample vapours extracted by the fibre were consid-ered as perfect gases (low concentration) and thus the influence ofhumidity has not been considered.

After sampling, fibres were then withdrawn from the flask anddirectly introduced into the injector port of the GC system.

In all experiments, stable conditions were reached before per-forming SPME (by performing several measurements at a stablelevel according to time).

GC sample analysis

Fibres were desorbed into the split/splitless insert of the GC at thetemperature of 270°C. The He flow rate was fixed at 1.5 mL min–1,and the injector was used in the splitless mode for 3 min. The GC oven temperature was programmed as follows: 50°C (3 min), 25°C min–1 to 160°C, 8°C min–1 to 240°C, 150°C min–1 to 300°C (2 min). The transfer line was held at 250°C and the detector at220°C. The MS was tuned to FC43 (perfluorotributylamine), andmass spectra were collected over the mass range (m/z) 50–650.Pesticide identifications were based on the comparison of their re-tention times with those of standard samples and their mass spec-tra (Fig. 4 and Table 1) obtained in the electron impact mode (EI).Quantification was made in the selective ion monitoring mode(SIM) by measuring peak areas of the fragment ions selected foreach pesticide and by comparing their values with the correspond-ing external calibration curves described in Table 1.

Results and discussion

Fibre selection

Based on the approach developed in the case of dichlorvos[30], the four most usual coatings, namely 100-µm PDMS,65-µm PDMS–DVB, 75-µm CN–PDMS and 85-µm PA,were successively tested for extracting procymidone,which was considered as representative of the selectedcompounds with a saturated vapour pressure in the middleof the selected range (Ps=1.8×10–2 Pa at 25°C). Corre-sponding extraction profiles are presented in Fig. 5; theseindicate that the 100-µm PDMS coating was the most sen-sitive fibre for extraction of procymidone. As a consequenceand because this result was in agreement with those ob-tained for dichlorvos, 100-µm PDMS was selected for thefollowing study.

Extraction profile

To visualise the partition equilibria between the fibre andthe atmospheric air samples for each of the 11 selectedmolecules (Table 1), extraction profiles were successivelyperformed by analysing 12 samples (i.e. including a blankone) according to the procedure described above and rep-resented schematically in Fig. 1 and with exposure timesranging from 3 to 193 min.

The first and main observation made was that relativechromatographic peaks intensities were very high for allcompounds (Table 1), even after few minutes of extrac-tion. Nevertheless, several types of curves have been ob-tained as indicated in Fig. 6, in which pesticides have beengathered according to the order of magnitude of observedsignals. Independently of this feature, chlorothalonil,cyanofos, malathion and folpet appeared nearly at equilib-rium after 40–60 min of exposure to the PDMS fibre. Incontrast, bioalletrin, fonofos, penconazole and quintozene,did not reach equilibrium within the 193 min of the exper-iment. The behaviours of chlorpyriphos methyl, procymi-done and trimethacarb were different: quasi-linear extrac-tion profiles were found over the duration of the experi-ment. This means that the 100-µm PDMS fibre can accu-mulate these compounds for a long time (i.e. at least ap-proximately 200 min).

Taking into account the above features, an extractiontime of 40 min was chosen to obtain significant signalswithin reasonably short analysis durations for air samples.

Repeatability

A series of six measurements were performed from vapoursaturated samples in the sampling flask according to theconditions described above (Fig. 1). Each extraction wasperformed for 40 min, and relative results are presented inTable 1. These showed RSDs ranging from 1.9% to 7.6%;four of the measurements were made on one day and thetwo others on the following day under the same experi-

Fig. 2 Assembly used for studying the linearity of HS-SPME sam-plings

Fig. 3 Proposed assembly for SPME air sampling

479

Table 1 Identification and repeatability

Compound Number Class Molecular Vapour Identification Retention Observed RSDc

weight pressure fragment ionsa time signalc (%)(amu) Pa (25°C) (amu) (min) (au)

Bioallethrin 1 Pyrethroid 302 4.4×10–2 136, 123b, 91, 79 9.01 1,028,142 4.18Trimethacarb 2 Carbamate 193 6.8×10–3 136b, 121, 91, 77 13.64 19,717,664 2.93Quintozene 3 Aromatic HC derivative 295 1.3×10–2 265, 249, 237b, 214 14.82 19,970,922 4.27Cyanofos 4 Organophorphorus 243 1.1×10–1 243, 127b, 125, 109 15.05 8,553,016 3.54Fonofos 5 Organophorphorus 246 2.8×10–2 246, 137b, 109, 81 15.14 48,014,491 3.21Chlorothalonil 6 Halocyanobenzene 266 7.6×10–5 266b, 229, 168, 124 15.34 241,656 5.42Chlorpyriphos methyl 7 Organophorphorus 286 5.6×10–3 286b, 271, 210, 197 16.26 8,540,794 4.79Malathion 8 Organophorphorus 330 5.3×10–3 173, 127b, 143, 99 17.23 608,508 1.92Penconazole 9 Azole 248 2.1×10–4 248, 161b, 159 18.27 475,646 2.83Folpet 10 N-Trihalomethylthio 297 1.3×10–3 297, 260b, 130, 104, 18.50 13,187 7.59Procymidone 11 Dicarboximide 283 1.8×10–2 283b, 255, 96, 67 18.57 53,560 4.32

am/z values used for identification of compoundsbValues are peaks corresponding to fragments used to quantifypeak areas using the SIM mode

cAverage of 6 measurements from previously vapour-saturated HSsamples extracted for 40 min as described in Fig. 1

Fig. 4a–e Chromatograms ob-tained in single ion monitoringmode (123+266 amu, 136+137+237 amu, 127+286 amu,127+283 amu, 161+260 amu,for a–e (top to bottom), respec-tively); bold numbers refer topesticides listed in Table 1

mental conditions. This particular experiment also provedthat in all cases the saturated vapour pressure is renewedbetween two experiments, within less than 40 min, whichwas the time needed for chromatographic analysis of thepreceding extracted sample.

Linearity and calibration

Routine standard air samples containing pesticide vapoursare not commercially available. In a first approach and toverify the linearity of observed signals versus pesticideconcentrations in air samples under atmospheric pressure,a series of headspace samplings were carried out at 25°Caccording to the described protocol (Fig. 2). As was justi-fied in the “Experimental”, the analyte concentration inthe headspace is assumed to be proportional to its concen-tration in the aqueous solution regardless of the extractiontemperature. Solutions of pesticides were then preparedaccording to the range indicated in Table 2 by diluting themost concentrated one with water, in the ratio 1, 0.75,0.50 and 0.25, respectively. Observed signals were plottedagainst corresponding HS concentrations expressed in thesame ratio. As a result of the very low vapour pressure ofsome of the compounds at very diluted concentrations, nosignals were observed for them at this temperature. An-other series was successfully analysed at 65°C for all theselected compounds. Figure 7 illustrates these results inthe cases of bioallethrin, chlorothalonil, cyanofos and pro-cymidone. Under these conditions, regression coefficientsgreater than 0.99 were found for all of the compounds ex-cept penconazole and cyanophos, for which values greaterthan 0.98 were obtained (curves were obliged to go throughthe origin as long as blank samples gave no signal).

Once the linearity of the extracting method was veri-fied, calibration curves relative to the sampling procedureindicated in Fig. 1 were realised by measuring a uniquepoint corresponding to a definite and known concentra-tion for each of the selected pesticides. This point wasgiven by recycled saturated vapours obtained from a mix-

480

Fig. 5 Selection of the fibre: extraction profiles from saturatedvapour air samples for procymidone by using 100-µm PDMS (◊),85-µm Polyacrylate (V), 75-µm Carboxen-PDMS (–) and 65-µmPDMS-DVB (O) fibres

Fig. 6 Extraction profiles of the 11 selected pesticides from satu-rated vapour air samples classified according to observed signal in-tensities: fonofos (O), trimethacarb (◊), quintozene (V), chlor-pyriphos methyl (–), cyanofos (T), bioallethrin (x), malathion (+),penconazole (E), chlorothalonil (�] ), procymidone (N), folpet (K)

ture of these compounds introduced into the large bottleused in the first assembly. Under these conditions, the ef-fective concentration of each pesticide was calculated ac-cording to the Marriott’s law equation:

(1)

where Cx is the concentration of the pesticide x in a satu-rated gas sample, T the absolute temperature (in K), R theperfect gas constant, and Ps is the corresponding equilib-rium vapour pressure of this pesticide at this temperature.Slopes of the calibration curves thus established are indi-cated in Table 2 as are the limits of detection (and quan-tification) that have been estimated on the basis of a ratiohigher than 3 (and 10) between the peak height and thebackground noise for each analyte, respectively. Under suchconditions, these limits ranged from 0.03 for chlorothalonilto 77 µg m–3 for procymidone. Surprisingly, the lowestLOD (30 ng m–3) was found for chlorothalonil although itssaturated vapour pressure was very low (7.6×10–5 Pa at25°C). For comparison, the LOD for Cyanofos was foundto be much higher (80 times), whereas its Ps was 1,500 timesmore important than that of chlorothalonil. From this ob-servation, it appears that vapour pressure is not the pre-dominant factor for explaining either the slopes of cali-bration curves or the observed detection limits. In fact,some very low volatile compounds (then with higher dis-tribution level in the vapour phase) exhibit higher extrac-tion efficiencies than others with higher vapour pressures.In other words, the adsorption of compounds onto the probeis not merely dependent on their concentration in thevapour phase. The corresponding partitioning coefficientsbetween vapours and the polymeric solid phase must alsobe considered. Actually, pesticides are partitioned be-tween the polymeric probe and the vapour phase accord-ing to their partitioning coefficients, respectively, and in-dependently of their vapour pressures. Under these condi-tions, even a compound characterised by a low vapourpressure can accumulate onto the fibre mainly because the

corresponding partitioning coefficient largely favours thecondensed form. As a consequence, the accumulation ofthe pesticide onto the fibre coating can be the result of animportant transfer of compound from the sample to theprobe through the vapour phase, independently of its con-centration in this phase.

Application to confined air samples in an experimental greenhouse

In the course of this study, a validation experiment wasrealised with procymidone under real-life conditions in asmall 8-m2 and 20-m3 experimental greenhouse in whichstrawberry cultivation was performed. Air concentrationsof this pesticide was assessed according to the proceduredescribed with the third assembly (Fig. 3) and plotted ver-sus time after treatment in Fig. 8. Ambient sampling tem-peratures were also noted and indicated on the same dia-gram. During the 80 h of this experiment, 8 measurementswere taken at the rate of twice a day, and procymidoneconcentration levels were observed between 200 and500 µg m–3 in strong correlation with corresponding temper-atures which varied between 10 and 20°C in the same pe-riod. These results are in agreement with those obtained bySieber and Mattusch [32] for the assessment of parathionand pirimicarb vapours under similar conditions in green-house air samples. The main difference with the case ofdichlorvos previously reported [30] is that no decrease ofthe procymidone concentration in air was observed ac-cording to the time spent after treatment. In fact, the con-centration that is measured in this case, corresponds tovapours emitted by procymidone sprayed onto the vegetalmatter but long after the sedimentation of the sprayingaerosol has occurred. Under these conditions and even fora low-volatile pesticide, it is not surprising to observeconcentration values mainly correlated to ambient tem-peratures. Nevertheless, a concentration of 324 µg m–3 was

� �� � ��=

481

Table 2 Linearity and quantification

Compound Program Linearity Conc. Calibration LODb LOQb

Number in saturated curve slopea (µg m–3) (µg m–3)R2 R2 Range of solution vapour phasea (au µg–1m3)(65°C) (25°C) concentration (µg L) (µg m–3)

Bioallethrin 1 0.997 0.999 4.0–200 192 5,351 10.4 18.2Trimethacarb 2 0.990 – 2.0–100 37200 530 0.11 0.23Quintozene 3 0.997 0.994 0.5–25 13200 1,512 0.11 0.22Cyanofos 4 0.98 0.98 2.0–100 830 10,298 2.41 6.26Fonofos 5 0.998 0.989 3.7–185 17200 2.780 0.17 0.32Chlorothalonil 6 0.989 0.98 3.6–180 29600 8.16 0.03 0.07Chlorpyriphos methyl 7 0.998 0.98 8.8–440 13200 646 0.11 0.22Malathion 8 0.999 – 5.0–250 861 706 1.74 3.83Penconazole 9 0.988 – 3.2–160 22600 21.0 0.09 0.19Folpet 10 0.998 – 2.4–120 84 156 5.91 15.3Procymidone 11 0.992 – 1.6–80 26 2,056 76.7 172.7

aValues obtained by Marriott law at room temperature condition (25°C) starting from vapour pressure listed in Table 1bEstimated limit of detection and quantification

found 2 h after treatment, and this particular result exem-plifies first the level of potential contamination that can befound in greenhouse, and second, the use that can be madeof this method for assessing the amount of pesticidebreathed by people working in the greenhouse.

Conclusion

The previously described method for assessing dichlorvoscontamination of confined atmospheres has been success-fully extended to 11 other pesticides selected from differ-ent chemical families with a large range of saturated vapourpressures. The observed efficiency of the method wasmainly related to the ability of the PDMS fibre to accu-mulate the pesticide via an important transfer from the“infinite” sample of air onto the coating. No correlationappeared with the saturated pressure of the compounds.Because of this, the method should also be useful for theassessment of a large scope of other organic air pollutants.

As was previously found for dichlorvos, which is con-sidered as quite a volatile molecule, the observed limits ofdetection with this method are in the µg m–3 level and farbelow the concentration that can be found in real profes-sional working conditions. In addition, sampling time isreduced to 40 min (i.e. about 10 times shorter than forother usual methods). This should be of real interest forassessing pesticide concentrations in air samples in manydifferent situations, as long as the studied atmosphere isstable and considered as a homogenous medium. In allcases, the method is direct and solvent-free. It can there-fore only reduce the global cost of analyses, which at pre-sent corresponds to a universal need.

Acknowledgements The authors acknowledge the financial sup-port from the Conseil Général de la Dordogne, the Centre Nationalde la Recherche Scientifique and the European Community MarieCurie Training Site Program.

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