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Determination of Organophosphorus Pesticides in Vegetables by Solid-Phase Extraction Cleanup and Gas Chromatography
Abstract and Figures
ABSTRAK Satu kaedah yang ringkas dan cepat telah dihasilkan untuk menentukan racun perosak jenis organofosforns di dalam sayur-sayuran dengan kromatografi gas. Sisa baki racun perosak diekstrak dengan aseton dan diklorometana. Ekstrak dibersihkan dengan turns ekstraksi fasa pepejal mod bercampur iaitu amina kuaterner dan aminopropil. Racun perosak ditentukan dengan kromatografi gas yang dilengkapkan dengan pengesan fotometrik nyala. Pengembalian 9 racun perosak untuk tigajenis sayur-sayuran iaitu lobak merah, timun dan sawi hijau pada aras 0.5 mg/kg adalah di antara 80.3% dan 115.0%. Pengembalian yang rendah telah diperoleh untuk methamidophos dan dimethoate. Keputusan ini dibandingkan dengan kaedah yang digunakan pada masa ini iaitu tanpa menggunakan pembersihan. ABSTRACf A simple and rapid gas chromatography method has been developed for simultaneous determination of organophosphorus pesticides in vegetables. Residues are extracted with acetone and dichloromethane. Extracts are cleaned up by a mixed-mode solid-phase extraction column, quaternary amine and aminopropyl silane. The pesticides are determined by gas chromatography using a flame photometric detector. The recoveries for 9 pesticides in three vegetables: carrot, cucumber and green mustard, fortified at 0.5 mg/kg were in the range of 80.3% to 115.0%. Lower recoveries were obtained for methamidophos and dimethoate. The results were compared to the method currently used in the laboratory which does not include any cleanup.
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... Italy, 1993 [20] , C 93/24). A survey on pesticide residues carried out by the Department of Agriculture Sarawak reported that 95% of total residue violation is caused by organophosphate pesticides (Lian and Seng, 2003) [39] . The pesticides are traditionally extracted using liquid-liquid extraction (LLE) (Fenoll et al., 2007;Wang et al., 2008;Hassan et al., 2010;Pirad et al., 2007) [22] . ...
... Italy, 1993 [20] , C 93/24). A survey on pesticide residues carried out by the Department of Agriculture Sarawak reported that 95% of total residue violation is caused by organophosphate pesticides (Lian and Seng, 2003) [39] . The pesticides are traditionally extracted using liquid-liquid extraction (LLE) (Fenoll et al., 2007;Wang et al., 2008;Hassan et al., 2010;Pirad et al., 2007) [22] . ...
This review presents an overview of analytical methods for the analysis of pesticide residues in fruit juices and vegetable paste. The most widely used detection technique for the determination of pesticides is mass spectrometry combined with gas chromatography. QuEChERS method was used for determining twenty seven pesticide residues as per standard guidelines of Association of Official Analytical Chemists (AOAC). The method involves extraction with acetonitrile, liquid-liquid partition with addition of MgSO4 and NaCl followed by dispersive SPE cleanup with PSA sorbent and the analysis was carried out with a GC-MS triple quad equipment.
... Italy, 1993 [20] , C 93/24). A survey on pesticide residues carried out by the Department of Agriculture Sarawak reported that 95% of total residue violation is caused by organophosphate pesticides (Lian and Seng, 2003) [39] . The pesticides are traditionally extracted using liquid-liquid extraction (LLE) (Fenoll et al., 2007;Wang et al., 2008;Hassan et al., 2010;Pirad et al., 2007) [22] . ...
... Italy, 1993 [20] , C 93/24). A survey on pesticide residues carried out by the Department of Agriculture Sarawak reported that 95% of total residue violation is caused by organophosphate pesticides (Lian and Seng, 2003) [39] . The pesticides are traditionally extracted using liquid-liquid extraction (LLE) (Fenoll et al., 2007;Wang et al., 2008;Hassan et al., 2010;Pirad et al., 2007) [22] . ...
This review presents an overview of analytical methods for the analysis of pesticide residues in fruit
juices and vegetable paste. The most widely used detection technique for the determination of pesticides
is mass spectrometry combined with gas chromatography. QuEChERS method was used for determining
twenty seven pesticide residues as per standard guidelines of Association of Official Analytical Chemists
(AOAC). The method involves extraction with acetonitrile, liquid-liquid partition with addition of
MgSO4 and NaCl followed by dispersive SPE cleanup with PSA sorbent and the analysis was carried out
with a GC-MS triple quad equipment. Three major groups of pesticides (organochlorine,
organophosphorus and synthetic pyrethoids) were taken for study. The method was applied to 9 fruit
juices (Apple, Pomegranate, Tomato, Guava, Mixed fruit, Mango, Litchi, Cranberry and Orange) & two
vegetable pastes (Ginger and Ginger-garlic). Most of the pesticides were found below the tolerance limit
i.e. 0.01 to 1.0 mg/kg, as per Food Safety and Standard Authority of India (FSSAI). Some pesticides like
Chlorpyrifos in orange juice (1.08 mg/kg) & Deltamethrin (1.28 mg/kg) in ginger garlic were detected
above the permissible limit of FSSAI
... Cypermethrin and deltamethrin are the most popular and widely used pyrethroid insecticides in many countries in the world, including Greece. Due to desirable environmental properties of short persistence and low toxicity to mammals combined with their broad spectrum of insecticidal activity and the comparatively shorter pre harvest intervals (PHIs), the pyrethroid insecticides are considered as a preferred alternative to organochlorine (Alvin, & Seng, 2003) and organophosphorus insecticides (Pang et al. 1994). Thus, cypermethrin and deltamethrin, two non-systemic pyrethroid insecticides, were selected in this study to estimate the variability factors of residue levels found within cauliflower and eggplant units grown commercially in northern Greece. ...
Variability of pesticide residues among food items is very important for consumer food safety evaluation and risk assessment. To estimate the residue variability of selected pesticides in individual food items of medium (eggplant) and large size vegetable commodities (cabbage, cauliflower and melon) an effective multi-residue method is required. Therefore, four multi-residue methods have been developed and validated by employing the quick, easy, cheap, effective, rugged, and safe (QuEChERS) extraction technique coupled with liquid chromatography-triple quadrupole mass spectrometry (LC-MS/MS) for the determination of thirteen pesticides in/on eggplant, ten pesticides in melon, and seven pesticides in/on cabbage and cauliflower, respectively. All the methods are simple, efficient, easy, accurate, and rapid. The average recoveries for all of the selected pesticides ranged from 71.8 to 112% with RSDr ≤ 16.2% for eggplant; 82 to 106% with RSDr ≤ 6% for melon; 80 to 110% with RSDr ≤ 16% for cabbage; 74-110% with RSDr ≤ 8% for cauliflower when processing samples of four fortification levels of 0.01, 0.05, 0.10 and 0.20 mg/Kg with all of the selected matrices except for eggplant for which the respective levels were 0.01, 0.05, 0.10 and 0.50 mg/Kg. The LOD values ranged from 0.001 to 0.003 mg/Kg for all the analytes. The LOQ was set at 0.01 mg/kg for all the analytes that was lower than the respective EU-MRLs. The correlation coefficients (R2) were ≥0.997 for all of the selected pesticides when matrix matched calibration standards were used. Matrix effects of eggplant, melon, cabbage and cauliflower for all the selected pesticides were estimated in this study. The effect of the matrix was prominent in eggplant for thiamethoxam, cypermethrin and deltamethrin and it was -69%, +57% and +93%, respectively, in melon for thiamethoxam and deltamethrin and it was -53% and +135%, respectively, in cabbage for cypermethrin and deltamethrin and it was +49% and +97%, respectively, and in cauliflower for cypermethrin and deltamethrin and it was +90% and +145%, respectively.
Variability is defined as the variation in concentrations of pesticide residues among individual units of any commodity. Variability factor is defined as the ratio between the 97.5th percentile of the residue levels and the mean of residue level of the same lot of a certain commodity. Variability factors are used in the acute dietary intake assessment of pesticides to account for the unit-to-unit residue variability in the composite samples.
All the analytical methods were applied successfully for pesticide residue analysis of eggplant, melon, cabbage and cauliflower fruits collected from different market places in Thessaloniki, Greece for the purpose of estimating the respective residue variability factors of pesticide residues existing among items of these commodities. A total of 142 samples of eggplant were analyzed. Among the analyzed samples, 67 (47% of the total no. of samples) had pesticide residues, of which 9 had multiple pesticides residues and 58 had single pesticide residues. Only one sample was found contaminated with dimethoate at a level above the EU-MRLs (European Commission, 2005). In the case of melon, a total of 122 samples were analyzed. Among the analyzed samples, 32 (26% of the total no. of samples) had pesticide residues, of which 2 had multiple pesticide residues and 30 had single pesticide residues. None of the samples were found contaminated with the detected pesticide residues at levels above the EU-MRLs (European Commission, 2005 & European Food Safety Authority, 2014).
A total of 132 fresh cabbage samples were analyzed. Among the analyzed samples, 41 (31% of the total no. of samples) had pesticide residues, of which 2 had multiple pesticide residues and 39 had single pesticide residues. Only one sample was found contaminated with deltamethrin at a level above the EU-MRLs (European Commission, 2005). In the case of cauliflower, a total of 120 samples were analyzed. Among the analyzed samples, 48 (40% of the total no. of samples) had pesticide residues. None of the samples were found contaminated with multiple pesticides residues. Only one sample was found contaminated with chlorpyrifos at a level above the EU-MRLs (European Commission, 2005).
Variability of pesticide residues originating from the analyisis of eggplant and cauliflower individual fruit units collected from respective supervised field trials were also estimated in this study. In these supervised field trials, cypermethrin and deltamethrin in mixture at the recommended application rates were applied as the last pre-harvest application and samples were collected at the specified PHI (pre-harvest interval). The estimated variability factors for cypermethrin and deltamethrin residues were 2.38 and 2.32, respectively for the samples of cauliflower, while it was 2.54 and 2.51, respectively for the samples of eggplant. Comparison between the residue levels estimated from the individual units and the composite samples of eggplant and cauliflower were investigated and found that the mean residue levels of both pesticides were higher in the composite samples than the mean of residue levels estimated from the individual samples.
In this study, the variation of cypermethrin and deltamethrin residue levels present in the exposed and non exposed (fruits covered with leaves) cauliflower units was also investigated and found that exposed cauliflower units bare higher concentrations of pesticide residues than those present in the cauliflower units covered with leaves (non-exposed). Furthermore, the variation of pesticide residue concentrations present in the upper and lower sections of individual cauliflower units was also investigated and it was found that most of the cypermethrin and deltamethrin residues were present in the upper portion of the cauliflowers units.
Within plants of eggplant unit to unit residue variation was also studied. The results revealed that exposed units of eggplant fruits (fruits collected from the outer periphery of the plant) had higher residues for both pesticides compared to the non exposed units of eggplant (fruits collected from the inner section of the plant).
The variability factors from the marketed samples of eggplant, melon, cabbage and cauliflower, respectively, were also estimated in this study. A total of 517 samples of 4 vegetables were collected from different market places of Thessaloniki in Greece. For eggplant, the estimated variability factors ranged from 1.00 to 7.09 with the detected pesticides; for melon, it was from 1.00 to 4.85; for cabbage, it was from 1.00 to 6.75, and for cauliflower, it was from 2.40 to7.12 with the detected pesticides. The average VFs for eggplant, melon, cabbage, and cauliflower were 3.89, 2.89, 5.00, and 5.11, respectively. Considering the commodity groups, the average VF for medium-sized crops was 3.89 while it was 4.33 for the large-sized crops. However, the average VF for all commodity crops was 4.11. Generally, the residue variability factors estimated from the marketed samples were higher than those found for the samples collected from the field trials. On the basis of the experimental data presented here a default VF value of 3 for field trials is adequately appropriate to be used in acute dietary intake assessment but for the marketed samples, a VF value should be reconsidered when more data are available, especially data concerning large-sized crops.
... 23,24 Nevertheless, cypermethrin and deltamethrin are widely used because of their low toxicity to birds and mammals and the comparatively short pre-harvest intervals. Due to their desirable environmental properties, cypermethrin and deltamethrin are considered as a preferred alternative to organochlorine 25 and organophosphorus insecticides. 26 However, VFs estimated for eggplants purchased from the marketplaces are limited. ...
Background:
Variability of pesticide residues among food items is very important when assessing the risks and food safety for the consumers. Therefore, the present study was undertaken to estimate the unit-to-unit residue variability factors for eggplant.
Results:
In total 120 samples from a trial field and 142 samples from different marketplaces in Thessaloniki, Greece were collected to estimate the variability of pesticide residues in eggplant units. They were extracted by QuEChERS method and the residues were determined by LC-MS/MS. For the field samples, the unit-to-unit variability factors (VFs) obtained for cypermethrin and deltamethrin residues were 2.54 and 2.51, respectively. The mean residue levels of both pesticides were higher in the composite samples than in the individual samples. The average VFs for the marketplace samples was 3.89. The eggplant units exposed to pesticides were higher in residues than the non-exposed units.
Conclusion:
The obtained variability factors in the marketplace samples were higher than those in the samples collected from the field trial. A default VF value of 3 for field trials is adequately appropriate to be used when assessing the acute dietary intake but a VF for the marketplace samples should be reconsidered with a larger data.
... Cypermethrin and deltamethrin are the most popular and widely used pyrethroid insecticides in many countries around the world, including Greece. Due to desirable environmental properties of short persistence and low toxicity to mammals combined with their broad spectrum of insecticidal activity and comparatively shorter pre-harvest intervals, the pyrethroid insecticides are considered as a preferred alternative to organochlorine [16] and organophosphorus insecticides. [17] Thus, cypermethrin and deltamethrin were selected in this study to estimate the respective VFs of pesticide residues found in cauliflower units grown commercially in northern Greece. ...
To estimate the variability of pesticide residue levels present in cauliflower units, a total of 142 samples were collected from a field trial of a cooperative farmer, and 120 samples were collected from different market places in Thessaloniki, Greece. The collected samples were extracted using the quick, easy, cheap, effective, rugged, and safe (QuEChERS) extraction technique, and the residues were determined by liquid chromatography–tandem mass spectrometry. The developed method was validated by evaluating the accuracy, precision, linearity, limit of detection (LOD), and limit of quantification (LOQ). The average recoveries for all the analytes, derived from the data of control samples fortified at 0.01, 0.05, 0.1, and 0.2 mg/kg, ranged from 74 to 110% with a relative standard deviation of ≤8%. The correlation coefficient (R2) was ≥0.997 for all the analytes using matrix-matched calibration standards. The LOD values ranged from 0.001 to 0.003 mg/kg, and the LOQ was determined at 0.01 mg/kg for all the sought analytes. The matrix effect was found to be at a considerable level, especially for cypermethrin and deltamethrin, amounting to +90% and +145%, respectively. For the field samples, the unit-to-unit variability factors (VFs) calculated for cypermethrin and deltamethrin were 2.38 and 2.32, respectively, while the average VF for the market basket samples was 5.11. In the market basket samples, residues of cypermethrin, deltamethrin, chlorpyrifos, and indoxacarb were found at levels ≥LOQ and their respective VFs were 7.12, 5.67, 5.28, and 2.40.
A GC-MS/MS method with low solvent consumption and easy operation was developed to simultaneously determine ten new-generation pesticides, namely fenobucarb, acetochlor, pretilachlor, fipronil, trifloxystrobin, fluazifop-p-butyl, isoprothiolane, tebuconazole, cypermethrin and difenoconazole in leafy vegetables. Influences from ultrasonic sample extraction and the clean-up steps to reduce matrix effects were investigated. Under suitable conditions, good linearity (deviation of back calculated concentration from true concentration lower than 20%) was achieved for all studied pesticides; the method detection limits (MDLs) ranged from 1.4 to 3.6 ng g⁻¹ wet weight. For mustard green and green onion the method yielded good recoveries at two spiking levels (20¹ and 100 ng g⁻¹) ranging from 80% to 111% (n = 5). The repeatability, expressed as relative standard deviation (RSD), was lower than 11% (n = 5). The method was successfully used to quantify pesticide residues in 207 vegetable samples (green onions, mustard greens, and lettuce) collected in Thua Thien Hue and Quang Binh Provinces, Central Vietnam. The insecticide cypermethrin was found at critical levels in 98% of the vegetable samples. Green onions had high pesticide residues with a significant number of samples containing pesticides at concentrations exceeding the maximum residue levels (MRLs).
Due to the extensive use of pesticides in all fresh consumptive vegetables and fruits, it is important to detect the residues of these compounds. Due to short period between spraying and harvest time, cucumber can show a higher level of contamination. This experiment was carried out to investigate the residues of Deltamethrin (EC 2.5%), in a Storm cultivar of cucumber in greenhouse. Plants were sprayed at recommended doses (0.5 g/lit) and, samples were collected 1 hour, 1, 3, 5 & 7 days intervals after treatment. Pesticides residues were analyzed using GC-MS. Results showed that Deltamethrin levels below maximum residue level recommended by codex (0.2 mg/kg) were detected 5 days after application and no residues were detected on the 7th day. The average of recovery from fortified samples with 0.5 ppm of Deltamethrin obtained 91.3%.
Urban agriculture in the Niayes zone of Dakar provides 60% of the vegetable needs of this region which has a high urbanization rate. Farmers in this area rely heavily on pesticides to protect crops from pests and diseases. The main objectives of this work were to try to answer the following questions : Do pesticide use patterns and management have an impact on the quality of environmental resources of the area? Does consumption of horticultural products and groundwater of this area pose a risk? We tried to bring answers through field surveys and analyses. The survey results showed the application of various pesticides belonging to organophosphates, organochlorines, carbamates and pyrethroids on a variety of speculations. Pesticides applied are not generally approved and some of them are persistent organic pollutants and thus prohibited for use in Senegal. Use practices (frequency, amount, storage conditions, packaging disposal) do not respect the rules of good agricultural practices. The analyses were performed on 80 groundwater samples, 119 of soil samples and 175 of vegetables collected at Niaga, Thiaroye, Cambérène and Malika during 4 campaigns. Results show high contamination levels of the environment with detection of 15 (in groundwater and vegetables) and 17 (in soil) pesticides out of 21. The molecules that have been detected with high frequencies in the matrices are those cited with frequencies greater than 6%. Nearly 56% of groundwater samples showed at least one substance with level exceeding the corresponding standard. 38% did not meet the standard set for total residues concentration. For vegetables, the percentages of exceeding standards ranged between 58 and 76% depending on the site. The estimated daily intake showed that nearly 80% of pesticide residues belong to the following WHO classes (extremely hazardous, highly hazardous and moderately hazardous). This observation evidences the risk of human exposure to contaminated food and water.
Gas chromatographic/mass spectrometric (GC/MS) methodology is presented for the determination, in banana-field soils, of the 4 most used organophosphorus nematicides in Martinique (French West Indies): cadusafos (Rugby), ethoprophos (Mocap), isazophos (Miral), and fenamiphos (Nemacur). After extraction with 2 successive solvent mixtures, ethyl acetate–dichloromethane (8 + 2, v/v) and ethyl acetate–acetone (7 + 3, v/v), cleanup was performed using solid-phase extraction cartridges (silica SPE). Fenamiphos and its metabolites were separated in the second eluate and then oxidized to sulfone. Analysis was performed by GC/MS in fragmentometric mode. Recoveries varied from about 75 to 90%. Limits of quantitation varied from 4 to 20 μg/kg fresh soil sample, depending on the nematicide.
A muitiresidue method based on solid-phase extraction cleanup and gas chromatography/ion trap mass spectrometry was developed to analyze 120 pesticides and pesticide metabolites in 2 soils with organic matter contents of 4.0 and 5.2%. Among the pesticides and the pesticide metabolites studied (almost all of which were spiked into soils at 0.075 ppm in triplicate), 107 (89%) of those spiked in soil containing 4.0% organic matter showed recoveries of 70-130%, as did 98 (82%) of those spiked in soil containing 5.2% organic matter. At a signal-to-noise ratio of 5 for all pesticides except chlorothalonil in soil containing 5.2% organic matter, limits of detection ranged from <1 to 15 ng/g.
A critical review of multiresidue analytical methods was performed to develop an easy procedure that can be applied with slight modifications to vegetable and animal food samples. The multiresidue method described Is applicable to the quantitative determination of 28 organophosphorus pesticides In fatty as well as nonfatty foods. The foods are divided Into 4 groups according to extraction process (acetone and acetone-water for samples with moisture content <45%) and cleanup (on active carbon- Cellte, on disposable mlnicolumns of Kieselguhr- type material, and on disposable mlnicolumns of bonded-phase silica, according to fat and pigment content). A further fractionation on silica-gel microcolumns can be Included In the procedure. A wide-bore column (SPB-5) with flame photometric detection operated in phosphorus mode (FPD-P) was chosen for gas chromatographic determination. Recoveries from apples, olive oil, whole milk, pasta, and eggs are reported. Two packed columns (4% OV-101 and SP2250- SP2401) with FPD-P were tested as confirmation columns. The method is suitable for a total diet study.
A new method for the extraction of pesticide residues and industrial chemicals with acetone is discussed. The extraction and partition steps are combined into one step by saturating the extraction solvent with NaCl and simultaneously driving away the water by dichloromethane. The organic phase, the volume of which is now independent of the original water content, is further dried with Na2SO4 and evaporated for GC- and LC-analysis.Eine neue Methode zur Extraktion von Pesticidrckstnden und Industriechemikalien wird beschrieben. Die Extraktion mit Aceton, die Verteilung dieser Verbindungen in die wsserige organische Phase durch Natriumchlorid und das Entfernen des Wassers aus der wsserigen organischen Phase durch Dichlormethan erfolgen in einem Schritt. Die organische Phase, deren Volumen nun vom Wassergehalt der Probe unabhngig ist, wird mit Na2SO4 getrocknet und zur GC- und LC-Analyse eingeengt.
A multiresidue screen for quantitative determination of 43 organophosphorus insecticides in 5 g of plant and animal tissues is described. The organophosphorus insecticides are extracted with methanol-dichloromethane (10 + 90, v/v) and cleaned up using automated gel permeation chromatography with hexane-ethyl acetate (60 + 40) eluant and in-line silica gel minicolumns. Concentrated extracts are analyzed by gas chromatography with flame photometric detection. The method recovers 43 organophosphorus insecticides in the range of 72 to 115%. Analysis of fortified bovine liver (n = 5) shows an average 95.9 +/- 4.8% recovery at the 0.05 micrograms/g level and 93 +/- 3.8% at the 0.5 micrograms/g level. Analysis of fortified bovine rumen content (n = 5) shows an average 98 +/- 4.2% recovery at the 0.1 micrograms/g level and 98.7 +/- 2.8% at the 1 micrograms/g level. Method detection limits ranged from 0.01 to 0.05 micrograms/g for the compounds studied using a nominal 5 gram sample.
Very few methods for detecting residues of pesticides in food or agricultural samples have undergone rigorous colloborative study and possess official AOAC status. The Chemical Residue Laboratory has formalized a method validation scheme to use when incorporating or developing new, unofficial methods. These methods are validated by assessing certain performance parameters: scope, specificity, linear range, accuracy, precision, limit of detection (LOD), and limit of quantitation (LOQ). For accuracy and precision assessment, 12 replicate fortifications must yield recoveries within the range of 70-120% with a coefficient of variation (CV) that compares favorably to the Horwitz CV. LOD and LOQ are equivalent to 3 and 10 times, respectively, the background signal contributed by a sample matrix blank. This criterion that we use for LOD/LOQ is not universal. In fact, because of differing definitions, we have encountered difficulties in enforcing a tolerance by using a registrant's method. This paper also presents an example of our method validation scheme, using a recent method development project for detecting sulfamethazine in raw milk. The sulfamethazine project also revealed unanticipated personnel problems, underscoring the importance of the human factor in quality assurance.
A simple and efficient cleanup method for gas chromatographic determination of 23 organophosphorus pesticides in crops including onion is described. The sample was extracted with acetone. The extract was purified with coagulating solution, which contained ammonium chloride and phosphoric acid, and then filtered by suction. The filtrate was diluted with NaCl solution and reextracted with benzene. The organic layer was evaporated and injected into a gas chromatograph equipped with a flame photometric detector (FPD) and fused silica capillary columns (0.53 mm id) coated with silicone equivalent to OV-1701, OV-1, and SE-52. Onion extract, which contained FPD interferences, was cleaned up on a disposable silica cartridge. Recoveries of most organophosphorus pesticides from spiked crops: mandarin orange, tomato, spinach, sweet pepper, broccoli, lettuce, and onion at levels of 0.02-0.28 ppm, exceeded 80%, but the water-soluble pesticides dichlorvos and dimethoate gave poor recoveries in all crops; the nonpolar pesticides disulfoton, chlorpyrifos, fenthion, prothiophos, and leptophos were not recovered quantitatively in spinach, sweet pepper, broccoli, and lettuce. IBP, edifenphos, phosmet, and pyridaphenthion were not recovered from onion because of adsorption to the silica cartridge. The detection limits ranged from 1.25 to 17.5 ppb on a crop basis.
A multiresidue method for the quantitative determination of organophosphorus pesticides in foods from the Food and Drug Administration's Total Diet Study is described. The organophosphorus pesticides are separated on the basis of polarity and determined in both fatty and nonfatty foods with a minimum of interferences. The foods analyzed included raw and cooked individual foods as well as combination dishes, water, and whiskey. Recoveries of 17 organophosphorus pesticides in 41 foods ranged from about 80 to 118%.
Methyl parathion (MPT; O,O-dimethyl-O-4-nitrophenyl phosphorothioate) and its active metabolite, methyl paraoxon (MPO; O,O-dimethyl-O-4-nitrophenyl phosphate), were isolated from raw milk by solid-phase extraction (SPE) and determined by gas chromatography with flame photometric detection. The SPE method was compared with a traditional liquid-liquid extraction (LLE) procedure to determine whether SPE had suitable sensitivity and better efficiency in extracting MPT and MPO from milk of cows and goats. Method detection limits were higher for SPE, but the differences were not significant (t-test). Recoveries of MPT and MPO from raw milk samples spiked at 0.05, 0.5, and 5.0 micrograms/mL ranged from 80.0 to 118%, and the coefficients of variation were usually less than 10% for both methods. LLE required more organic solvents and was more time consuming compared with SPE.
Diatomaceous earth columns used with reversed and normal solid phase extraction (SPE) cartridges were evaluated for the quantitative determination of a number of organophosphorus (OP) and organochlorine (OC) pesticide residues in edible vegetable oils and butterfat. An oil or fat sample (about 2 g) in hexane was passed through a diatomaceous earth (Extrelut QE) column and a C18 bonded silica (ODS) SPE cartridge, resulting in the separation of the pesticides from about 98% of the lipids. The eluate was split in half, with the first portion concentrated into acetone for the determination of OP pesticides by gas chromatography with flame photometric detection (GC-FPD). The other half was passed through an Alumina-N SPE cartridge for additional cleanup of lipid matrix to determine OC pesticides by GC with electron-capture detection (GC-ECD). Average recoveries from fortified samples were greater than 89% for the pesticides studied.