Gas Chromatography-electron Capture Detection Research Articles

Application of liquid-phase microextraction to the analysis of trihalomethanes in water

A liquid-phase microextraction method for the determination of trihalomethanes (THMs) including chloroform (CHCl 3), bromodichloromethane (CHBrCl 2), dibromochloromethane (CHBr 2Cl) and bromoform (CHBr 3) in water samples was developed, with analysis by gas chromatography-electron capture detection (GC-ECD). After the determination of the most suitable solvent and stirring rate for the extraction, several other parameters (solvent drop volume, extraction time and ionic strength of the sample) were optimized using a factorial design to obtain the most relevant variables. The optimized extraction conditions for 5 mL of sample volume in a 10 mL vial were as follows: n-hexane an organic solvent; a solvent drop volume of 2 μL; an extraction time of 5.0 min; a stirring rate of 600 rpm at 25 °C; sample ionic strength of 3 M sodium chloride. The linear range was 1–75 μg L −1 for the studied THMs. The limits of detection (LODs) ranged from 0.23 μg L −1 (for CHBr 2Cl) to 0.45 μg L −1 (for CHCl 3). Recoveries of THMs from fortified distilled water were over 70% for a fortification level of 15 μg L −1, and relative standard deviations of the recoveries were below 5%. Real samples collected from tap water and well water were successfully analyzed using the proposed method. The recovery of spiked water samples was from 73% to 78% with relative standard deviations below 7%.

Evaluation of organochlorine pesticides in serum from students in Coimbra, Portugal: 1997–2001

In 1997, 1999, 2000, and 2001, in an attempt to evaluate the contamination level of a Portuguese population, organochlorine pesticide residues were evaluated in human serum from students of the University of Coimbra. Concentrations of selected organochlorine pollutants ( α-, β-, and γ-HCH, aldrin, dieldrin, HE, HCB, p, p′-DDT, o, p′-DDT, p, p′-DDE, p, p′-DDD) and endosulfan sulfate was measured with gas chromatography–electron capture detector. Our objective is to point out the general levels of pesticide contamination and the differences between the four populations; and together with this, if a connection could be established with gender or the residence area of the subjects. Endosulfan sulfate, p, p′-DDE, o, p′-DDT, and p, p′-DDD were the most frequently identified residues. Endosulfan sulfate present the highest concentrations for all subjects, 42.6 μg/l, with concentrations ranging from undetected to 1295.5 μg/l. Between DDT, isomers, and analogues, o, p′-DDT, and p, p′-DDT presented the highest levels, 24.8 and 21.9 μg/l, respectively. Mean total DDT levels were higher than mean total HCH levels. For ∑-DDT, the highest levels were found among female gender and urban samples. An opposite situation was found in ∑-HCH: males presented higher levels than females. The mean concentration of organochlorine pesticide residues, present in the student populations, showed that it is among the highest levels of contamination, when compared with others from Europe, Asia, and America.

Determination of pyrethroid, organophosphate and organochlorine pesticides in water by headspace solid-phase microextraction

Simultaneous determination of pyrethroid, organophosphate (OP) and organochlorine (OC) pesticides in water was achieved with headspace solid-phase microextraction (HS-SPME) followed by gas chromatography-electron-capture detection (GC-ECD). The parameters affecting HS-SPME of pesticides from water were optimized, including extraction temperature, sample and headspace volumes, and sodium chloride amounts. The effects of desorption temperature, desorption time, and position of the fibre in the GC inlet were also investigated. Extraction temperature was the most important factor affecting the recoveries of analytes, and the optimized temperature was 96°C. The addition of salt did not increase extraction efficiencies of the pesticides from the water. The optimized desorption conditions in the GC were as follows: desorption time of 10 min; desorption temperature of 260°C; and a 2 cm position of the fibre in the inlet. The method detection limits were in the low-ng/L level with a linearity range of 50–1000 ng/L for the OCs, 50–5000 ng/L for the OP, and 50–20 000 ng/L for the pyrethroids. These data demonstrated that HS-SPME is a sensitive method for the determination of pyrethroid, OC, and OP pesticides in water.

Levels of selected pesticides in honey samples from Kahramanmaraş, Turkey

In this study 32 pesticide residues and eight polybrominated diphenlyl ether (PBDE) congeners were measured in nine honey samples from Kahramanmaraş, Turkey. A new method based on the best recovery was column extraction with n-hexane/acetone followed by gas chromatography electron-capture detection (GC-ECD), and mass spectrometry (GC–MS). Generally the pesticide levels were low in the honey samples. γ-HCH and PCB 28 were being measured in all honey samples. The sum of HCHs in samples varied between 0.71 and 2.47 ng/g. Malathion, bromophos methyl, cis-HCE, chlordane, endrin, p,p′-DDE and o,p′-DDD were not detectable. The mean values of α-HCH and β-HCH were 0.60 and 0.52 ng/g. The mean values of HCB, α-chlordan, trans-nonachlor, cis-nonachlor, Heptachlor, aldrin, bromophos ethyl, trans-HCE, α-endosulfan, β-endosulfan, dieldrin were 0.30, 0.05, 0.14, 0.84, 0.04, 0.06, 2.74, 0.03, 0.09, 0.27, 0.36 ng/g respectively. In none of the samples PBDEs were detected.

A simple supported liquid hollow fiber membrane microextraction for sample preparation of trihalomethanes in water samples

A simple and efficient liquid-phase microextraction (LPME) technique using a supported liquid hollow fiber membrane, in conjunction with gas chromatography–electron capture detector has been developed for extraction and determination of trihalomethanes (THMs) in water samples. THMs were extracted from water samples through an organic extracting solvent impregnated in the pores and filled inside the porous hollow fiber membrane. Our simple conditions were conducted at 35 °C with no stirring and no salt addition in order to minimize sample preparation steps. Parameters such as types of hollow fiber membranes, extracting solvents and extraction time were studied and optimized. The method exhibited enrichment factors ranged from 28- to 62-fold within 30 min extraction time. The linearity of the method ranged from 0.2 to 100 μg l −1. The limits of detection were in the low μg l −1 level, ranging between 0.01 and 0.2 μg l −1. The recoveries of spiked THMs at 5 μg l −1 in water were between 98 and 105% with relative standard deviations (RSDs) less than 4%. Furthermore, the method was applied for determination of THMs in drinking water and tap water samples was reported.

Determination of endocrine disruptors in Kafue lechwe ( Kobus leche kafuensis) samples from the Lochinvar National Park of Zambia

Analysis of serum, whole blood and liver tissue samples from Kafue lechwe in the Lochinvar National Park of Zambia for suspected endocrine disrupting compounds revealed high concentrations for some of the compounds. 45 samples of serum, whole blood and liver tissue were extracted by liquid–liquid extraction followed by an analysis using Gas Chromatography-Electron Capture Detection (GC-ECD). The following endocrine disruptors were analyzed: deltamethrin, aldrin, endosulfan, dieldrin, pp-DDD, heptachlor, d-t-allethrin, pp-DDE, endrin and pp-DDT. For all the samples, dieldrin showed the highest concentration ranging from 1.7 to 44.4 μg/ml in serum and whole blood sample extracts and 0.10–5.1 μg/g wet weight in liver sample extracts. The most frequently detected was deltamethrin in 62% of the samples. Percent recoveries in spiked laboratory blanks ranged between 60% and 100% while calculated detection limits ranged from 0.004 to 0.21 μg/ml for all the endocrine disruptors evaluated. Where endocrine disruptors were detected, the concentrations of most of them far exceeded the maximum residue limits (MRLs) and the extraneous maximum residue limits (EMRLs) set by the Codex Alimentarius of the United Nations (UN), Food and Agricultural Organization (FAO).

Development and Characterization of Stable Sediment-Free Anaerobic Bacterial Enrichment Cultures That Dechlorinate Aroclor 1260

We have developed sediment-free anaerobic enrichment cultures that dechlorinate a broad spectrum of highly chlorinated polychlorinated biphenyls (PCBs). The cultures were developed from Aroclor 1260-contaminated sediment from the Housatonic River in Lenox, MA. Sediment slurries were primed with 2,6-dibromobiphenyl to stimulate Process N dechlorination (primarily meta dechlorination), and sediment was gradually removed by successive transfers (10%) to minimal medium. The cultures grow on pyruvate, butyrate, or acetate plus H(2). Gas chromatography-electron capture detector analysis demonstrated that the cultures extensively dechlorinate 50 to 500 mug/ml of Aroclor 1260 at 22 to 24 degrees C by Dechlorination Process N. Triplicate cultures of the eighth transfer without sediment dechlorinated 76% of the hexa- through nonachlorobiphenyls in Aroclor 1260 (250 mug/ml) to tri- through pentachlorobiphenyls in 110 days. At least 64 PCB congeners, all of which are chlorinated on both rings and 47 of which have six or more chlorines, were substrates for this dechlorination. To characterize the bacterial diversity in the enrichments, we used eubacterial primers to amplify and clone 16S rRNA genes from DNA extracted from cultures grown on acetate plus H(2). Restriction fragment length polymorphism analysis of 107 clones demonstrated the presence of Thauera-like Betaproteobacteria, Geobacter-like Deltaproteobacteria, Pseudomonas species, various Clostridiales, Bacteroidetes, Dehalococcoides of the Chloroflexi group, and unclassified Eubacteria. Our development of highly enriched, robust, stable, sediment-free cultures that extensively dechlorinate a highly chlorinated commercial PCB mixture is a major and unprecedented breakthrough in the field. It will enable intensive study of the organisms and genes responsible for a major PCB dechlorination process that occurs in the environment and could also lead to effective remediation applications.

Uncertainty associated to the analysis of organochlorine pesticides in water by solid-phase microextraction/gas chromatography–electron capture detection—Evaluation using two different approaches

As the performances of analytical instrumentation are being gradually enhanced, the limits of detection become increasingly lower, allowing more environmental contaminants to be determined in different matrices. Problems emerge when dealing with data from different origins, once the uncertainty of the results is difficult to be compared, especially if its calculation procedure is rather different, as very often happens. Samples of two organochlorine pesticides of somewhat opposite characteristics (lindane and heptachlor, classified as persistent organic pollutants—POPs) were analyzed in aqueous media using headspace solid-phase microextraction (SPME) prior to gas chromatography–electron capture detection (GC–ECD) and this methodology was in-house validated. Detection limits of 0.097 and 0.050 μg l −1, average intermediate precision of 11.6% and 27.5%, and average recovery of 95.6% and 103.0%, for lindane and heptachlor, respectively, were found. In the absence of available interlaboratory studies to assess the reliability of the results, the expanded uncertainty was calculated following two different approaches ( bottom-up/Eurachem and modified top-down) and the results were compared. Globally it was clearly shown that, for both pesticides, the lower the concentration range, the higher the uncertainty associated to the results. Expanded uncertainties estimated by bottom-up/Eurachem approach varied from 51% to 14% for a lindane concentration range of 0.1–1 μg l −1, and from 48% to 24% for a heptachlor range of 0.1–2 μg l −1. Modified top-down approach pointed to 44% (lindane and heptachlor) in the same ranges, meaning that a uniform procedure for uncertainty estimation should be adopted.

Residue contents of captan and procymidone applied on tomatoes grown in greenhouses and their reduction by duration of a pre-harvest interval and post-harvest culinary applications

In this study, controlled applications of captan and procymidone were carried out on tomatoes grown in two different greenhouses at different times. The first group of samples were collected immediately after the application and the second group were collected 14 days later. Additionally, control samples were collected before application. The effects of washing, peeling and predetermined storage period, at 4 °C for 7 and 14 days, on the reduction of residue levels in the plant tissues were investigated in the two groups. A gas chromatographic method using acetone, dichloromethane and petroleum ether as extraction solvents, was used to analyse residual captan and procymidone in tomatoes, with obtained recoveries higher than 83%. Captan and procymidone were determined by gas chromatography-electron capture detection (GC-ECD), using a 5% phenylmethylpolysiloxane-coated fused-silica capillary column. Results showed that waiting for the recommended pre-harvest intervals, indicated on the prospectuses of both pesticides, lowered the residue levels to within acceptable limits. Culinary applications, such as washing and peeling and refrigeration storage, were also effective in reducing the residue levels.

A novel headspace solid-phase microextraction method for the exact determination of organochlorine pesticides in environmental soil samples

A novel method of determining organochlorine pesticides (OCPs) is described. It is based on solid-phase microextraction (SPME) and gas chromatography-electron capture detection. During the development of the method, soil samples were prepared, spiked with standard solution, and then aged for some time. Extraction conditions such as the extraction time, the NaCl content, the volume of water, the extraction temperature and the desorption time were investigated and optimized. The limits of detection obtained using the method ranged from 0.10 to 0.51 ng g(-1), and relative standard deviations were lower than 10% for most organochlorine pesticides. Real soil samples were successfully analyzed using the proposed method. The results from the method developed here were in good agreement with those obtained using ultrasonic extraction. The result demonstrates that aging soils spiked with standard solution is an important method development step, because the soil samples obtained using this approach are more like real soils than those obtained when aging is not used.

Performance characteristics of an analytical procedure for determining chloramphenicol residues in muscle tissue by gas chromatography–electron capture detection

Validation of an analytical method for determining chloramphenicol residues in muscle tissue by gas chromatography-electron capture detection (GC-ECD) was performed according to the latest European Union criteria for the analysis of veterinary drugs in food, laid down by Commission Decision 2002/657/EC. The method using the meta isomer of chloramphenicol as an internal standard proved to be very selective, specific to other related phenicols and accurate to within +3.6% at a concentration level of 8.9 microg/kg, as present in the certified reference material available. The correlation coefficient of the calibration curve was 0.9991. At all three fortification levels studied (0.3, 0.45 and 0.6 microg/kg), repeatability and intra-laboratory reproducibility were <8 and < or =9%, respectively. The decision limit (CCalpha) and detection capability (CCbeta) were 0.07 and 0.12 microg/kg, respectively. The validation results and the results of participation in an international inter-laboratory proficiency test indicate that the method presented is completely suited for regulatory control to screen and quantify chloramphenicol residues in various muscle tissues on a routine basis.

Application of lipid peroxidation and protein oxidation biomarkers for oxidative damage in mammalian cells. A comparison with two fluorescent probes

We recently developed two biomarker sets for oxidative damage: one for determination of lipid peroxidation (LPO) degradation products; acetaldehyde, propanal, butanal, pentanal, hexanal, heptanal, octanal, nonanal, malondialdehyde and acetone, by a gas chromatography-electron capture detection method, and the other for protein oxidation products such as o, o′-dityrosine, by an isotope dilution high performance liquid chromatography–tandem mass spectrometry method. In the present study, we explored the possibility to utilize these biomarkers for determining the oxidative damage in liver mammalian cells in vitro. Two different treatments were chosen for inducing oxidative stress in Chinese Hamster ovary cells: menadione and copper plus hydrogen peroxide (Cu 2+/H 2O 2). Cells were incubated with the model compounds in the presence or absence of vitamin E and C, and cytotoxicity was evaluated by a nuclear-dye method. Results were compared to two fluorescent probes, H 2DCF-DA and C 11-BODIPY 581/591, which have been used for determining the formation of free radicals in the cells. From ten LPO degradation products, eight were increased significantly following incubation with menadione in cell lysate or incubation media. Menadione-induced oxidative stress was also confirmed by oxidation of fluorescent probes. However, no increased formation of protein oxidation products was observed. Vitamin E and C did not diminish the formation of LPO degradation products that were increased by menadione. Although Cu 2+/H 2O 2 did not induce oxidation of fluorescent probes, it induced formation of six out of ten LPO degradation products. Vitamin E and C did not diminish the formation of LPO degradation products; vitamin C even substantially increased the formation of acetaldehyde and propanal, which is in line with its reported prooxidant action under certain conditions. Vitamin C also caused two-fold increase in Cu 2+/H 2O 2-induced o, o′-dityrosine formation when applied simultaneously. In conclusion, our present results show that the LPO biomarker set can be used for evaluation of oxidant capacity and the toxic potential of various chemicals in an in vitro cell model. These biomarkers might even be more sensitive than measuring protein oxidation products or oxidation of fluorescent probes.

A survey and measurement of residues of lindane (organochlorine pesticides) in four species of the most consumed fish in the Caspian Sea (Iran)

In this study, samples of four species of the most consumed fish (sefid, koli, kilca and kafal fish) were analysed for concentrations of lindane (organochlorine pesticides). Fish were caught using electric fishing at four sites (Chalous and Babolsar cities, Khazar Abad and Miankaleh regions) in the Mazandaran provinces of Iran. Quantitative determination of the lindane was performed by gas chromatography electron-capture detection (GC-ECD). Samples contained detectable concentrations of lindane, but at concentrations below the maximum residue limit (MRL). No differences were found in the lindane concentrations between the types of fish at each site, but there were two groups of sites that were significantly different from one another in terms of lindane concentrations: sites II-IV < site I (P <0.05). However, the concentrations of lindane residues in the muscle were found to be less than the FAO/WHO (1993) recommended permissible intake and should not be of public concern in Mazandaran province.

Solid-phase extraction cleanup of tomato samples for the determination of pesticide residues by gas chromatography-electron capture detection

Extracts of tomato samples, obtained using acetone solvent followed by liquid–liquid partition with a mixture of dichloromethane and light petroleum (40–60°C), were subjected to cleanup with solid-phase extraction (SPE) columns for the simultaneous multiclass determination of 12 pesticides with different physicochemical properties (log P ow = 0.7 to > 6). Silica, aminopropyl (NH2), graphitized carbon black (GCB), octadecyl (C-18) with GCB and the mixed-mode SAX/PSA (SPE) columns were evaluated. The sample cleanup provided by these columns was evaluated using gas chromatography with electron capture detection. The mixed-mode SAX/PSA columns were found to provide the most effective cleanup, along with the (NH2) columns, removing the greatest number of sample matrix interferences. The GCB sorbents also remove pigments but do not remove noticeable chromatographic interferents. The silica columns did little to eliminate the matrix effect for the compound dimethoate. Likewise, the C-18 in combination with the GCB sorbents did little to eliminate matrix interferences.

Permeation of Telone C-35 EC™ and chloropicrin through protective gloves

Telone is a potent volatile liquid chlorinated hydrocarbon pesticide based on 1,3-dichloropropene that is applied without dilution for fumigation purposes, and so poses an inhalation and air pollution threat, as proven by past monitoring. 1,3-Dichloropropene also causes allergic skin effects, is absorbed through the skin, and metabolites have been shown to be excreted after skin absorption, so making it a skin exposure threat too, one that may become most important in the situations of adequate respirator protection or cleaning up spills. It is often coformulated with agents like chloropicrin, a chemical warfare agent, to substitute for methyl bromide fumigant. The aim of the study was to assess if nitrile and laminated gloves provided adequate protection against Telone C-35 EC™, using an ASTM-type I-PTC-600 permeation cell containing disposable (Safeskin™) and chemically-resistant (Sol-Vex™) nitrile and laminated (Barrier™ and Silver Shield™) glove materials with hexane liquid collection. Analyses of cis- and trans-1,3-dichloropropene and chloropicrin in the collection fluid at various times were performed on a moderately polar capillary column, using gas chromatography–electron capture detection by the internal and external standards methods. Both nitrile materials were degraded by the formulation and pure chloropicrin, and so were unsuitable for protection. Both laminated glove materials offered some protection with Silver Shield™ the better, since less mass had permeated by 8 h, but the extent of protection was still inadequate, as illustrated by a risk assessment of the skin exposure situation. It is recommended that Viton gloves be worn rather than the laminated ones when Telone C-35 EC™ is handled. Laminated gloves may protect against pure chloropicrin. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 100: 18–25, 2006

Drug screening in urine by cloned enzyme donor immunoassay (CEDIA) and kinetic interaction of microparticles in solution (KIMS): a comparative study

Two commercially available drug-screening assays were evaluated: the Roche kinetic interaction of microparticles in solution (KIMS) assay and the Microgenics cloned enzyme donor immunoassay (CEDIA). Urine samples from known drug-abuse patients were analyzed for amphetamines, barbiturates, benzodiazepines, benzoylecgonine, cannabinoids, LSD, methadone and opiates. Samples with discordant findings for the two assays were analyzed by gas chromatography/mass spectrometry (GC/MS) or gas chromatography/electron capture detection (GC/ECD). Amphetamines showed 96.0% concordant results, with two false positive findings by CEDIA, three by KIMS and a further two false negatives by KIMS. Barbiturates showed 99.4% concordant results, with one false negative by KIMS. Benzodiazepines showed 97.4% concordant results, with two false negatives by KIMS (cutoff 100 microg/L, CEDIA cutoff 300 microg/L). Benzoylecgonine showed 17.8% concordant positive and 82.2% concordant negative results and no false finding by either assay. Cannabinoids showed 99.3% concordant results, with one sample negative by KIMS at a cutoff of 50 microg/L and positive by CEDIA (cutoff 25 microg/L). For LSD, 6.7% of findings were not in agreement. Methadone showed 97.5% concordant results, with two false positives by CEDIA, and one false positive and one false negative by KIMS. Opiates showed 96.9% concordant results, with no false KIMS results, but four false positives by CEDIA. The results indicate that the agreement of the CEDIA and KIMS results for the eight drugs is rather good (93.3-100%).

Monitoring of Organochlorine Pesticide Residues in Summer and Winter Vegetables from Agra, India – A case study

Analysis of summer and winter vegetable samples during 2002-2003 for pesticidal contamination was carried out on Gas Chromatograph-Electron Capture Detector with capillary columns. The contamination levels of winter vegetables (average concentration of 4.57, 6.80 and 5.47 ppb respectively for Lindane, Endosulphan and DDT) were found to be slightly higher than the summer vegetables (average concentration of 4.47, 3.14 and 2.82 ppb respectively for Lindane, Endosulphan and DDT). The concentration of these organochlorine pesticides in summer and winter vegetables were well below the established tolerances but continuous consumption of such vegetables even with moderate contamination level can accumulate in the receptor's body and may lead to chronic effects that could be fatal.

Matrix solid phase dispersion–Soxhlet simultaneous extraction clean-up for determination of organochlorine pesticide residues in tobacco

A novel method combining matrix solid phase dispersion (MSPD) with Soxhlet simultaneous extraction clean-up (SSEC) was developed. Being a single-step extraction and clean-up procedure, it could be used instead of multistep solvent extraction and Florisol column clean-up. It not only reduces sample contamination during the procedure, but it also decreases the amount of organic solvent needed. The retention times of standards were used to qualitatively assess the method, and the external standard method was used to quantitatively assess it. Residues of organochlorine pesticides (OCP) in tobaccos were determined by gas chromatography-electron capture detection (GC-ECD), and their identities were confirmed by the standard addition method (SAM). The performance of the method was evaluated and validated: the detection limit was 0.01-0.02 microg g(-1), relative standard deviations were 5-26%, and recoveries were 72-99% at fortification levels of 0.10, 1.00 and 10.0 microg g(-1). The analytical characteristics of MSPD-SSEC compared very favorably with the results from the classical multistep solvent extraction and Florisol column clean-up method.

Monitoring of Polychlorinated Biphenyls in Surface Water Using Liquid Extraction, GC/MS, and GC/ECD

A rapid and reliable analytical method, at trace level concentration was developed and validated for monitoring polychlorinated biphenyls (PCBs) in Jordanian surface water. The method combines the advantage of liquid extraction together with gas chromatography‐mass spectrometry (GC/MS) and gas chromatography‐electron capture detector (GC/ECD). The performance of the method was evaluated by analyzing certified reference material (CRM) of the analytes and applied on real water samples collected from different sites in Jordan. A mixture of 60∶40 dichloromethan‐petroleum ether was chosen as a convenient binary solvent for liquid–liquid extraction. The GC conditions for GC/MS were optimized using He as a carrier gas, temperature programming, and chlorpropham as an internal standard (IS). The conditions for GC/ECD were performed using N2 gas and a temperature program from 160 to 280°C with different increasing rates. The method of GC/MS in the selective ion mode (SIM) gave linear relationships for all PCBs tested between 0.60–6.0 µg/l with R 2=0.9934 (n=7×18). Recoveries from spiked water samples ranged between 87.6 and 91.4%. The mean accuracy and precision obtained were 4.9% and 2.16%, respectively. The mean of detection limit was 0.14±0.04 µg/l. In GC/ECD, linear relationships for all PCBs examined over the range of 0.3–2.4 µg/l was verified as characterized by a linear regression equation and correlation coefficient, R 2=0.9915 (n=12). The average precision and accuracy were 4.86% and 5.21%, respectively. Analyses results clarified that none of the examined Jordanian water samples contained any of the searched for PCBs within the detection limit achieved.

MONITORING OF PESTICIDE RESIDUES IN RIVER NILE WATER FROM EGYPT BY SOLID-PHASE EXTRACTION FOLLOWED BY GAS CHROMATOGRAPHY AND GAS CHROMATOGRAPHY–MASS SPECTROSCOPY

Solid-phase extraction (SPE), gas chromatography electron capture detector (GC-ECD) and gas chromatography nitrogen-phosphorous detector (GC-NPD) and gas chromatography–mass spectroscopy (GC-MS) were applied for trace-level de-termination of 20 pesticides in river nile water. Samples were collected from March to October 2003 from different sites located in Greater Cairo, Egypt. First, extrac-tion by on-site solid-phase extraction of 1 liter from field and laboratory spiked and unspiked (raw river water) samples using poly-divinyl benzene-N-vinyl pyrolidine cartridge based sorbent. Next, water extracts were subject of analysis by GC-ECD and GC-NPD. Next, selected samples that were positive to GC-ECD or GC-NPD were analyzed by GC-MS in order to improve the determination of detected pesti-cides. Recoveries from laboratoy spiked samples were > 85% for 16 of the 20 com-pounds with % relative standard deviation (% RSD) in the 5 to 10 % range. The lowest recoveries were for aldrin, 52 % and prothiofos, 48 %. A similar trend was observed with p,p-DDE and p,p-DDT values. Field spike results also indicated high % recovery for most of the target compounds. Values were > 85% for 12 of the 20 analytes, as was the case in laboratory spikes, Aldrin, 54 % and prothiofos, 55 % yielded the lowest values. Overall field spike recovery reproducibility was lower since % RSDs were higher, 15-40 %. Overall results indicated a relatively high de-gree of accuracy and precision could be achieved for most of the target compounds by methods applied in present study.