Frank J. Schenck

Does further clean-up reduce the matrix enhancement effect in gas chromatographic analysis of pesticide residues in food?

Sample extracts of apples, peas, green beans, oranges, raspberries, clementines, carrots, and wheat obtained using the Food and Drug Administration (acetone extraction) and Canadian Pest Management Regulatory Agency (acetonitrile extraction) multiresidue methods for pesticides were subjected to clean-up using different solid-phase extraction (SPE) cartridges in an attempt to reduce or eliminate the matrix enhancement effect. The matrix enhancement effect is related to the blocking of active sites on the injector liner by matrix components, thereby increasing signal in the presence of matrix versus standards in solvent in which the pesticides themselves interact with the active sites. Graphitized carbon black (GCB) was often used in combination with various anion-exchange SPE cartridges. The extracts were then spiked with organophosphorus insecticides. These process standards were then compared to standards in acetone of the same concentration using gas chromatography with flame photometric detection or ion trap mass spectrometric detection. Sample matrix enhancement varied from little to no effect for some pesticides (e.g. chlorpyrifos, malathion) to >200% in the case of certain susceptible pesticides. The GCB removed color components but showed little effect in reducing matrix enhancement by itself. The anion-exchange cartridges in combination with GCB or not, substantially reduced the matrix enhancement effect but did not eliminate it.

Chromatographic methods of analysis of antibiotics in milk

The widespread use of antibiotics in dairy cattle management may result in the presence of antibiotic residues in milk. While rapid screening tests are commonly used to detect the presence of antibiotics in milk, more accurate chromatographic methods are required by government regulatory agencies to identify and confirm the identity and quantity of antibiotic present. This paper review recent developments in the chromatographic determination of antibiotic residues in milk.

Comparison of solid-phase extraction sorbents for cleanup in pesticide residue analysis of fresh fruits and vegetables

Sample extracts of various commodities, obtained using the US Food and Drug Administration (acetone extraction) and Canadian Pest Management Regulatory Agency (acetonitrile extraction) methods for pesticides were subjected to cleanup with solid phase extraction (SPE) columns. Graphitized carbon black (GCB), octadecylsilyl (C-18), strong anion exchange (SAX), aminopropyl (-NH 2 ), and primary secondary amine (PSA) SPE columns were evaluated. The relative sample cleanup provided by these SPE columns was evaluated using gas chromatography with electron capture, flame photometric, and mass spectrometric detection. The -NH 2 and PSA columns were found to provide the most effective cleanup, removing the greatest number of sample matrix interferences. The GCB columns removed most of the visible plant pigment in the extracts, but did little to eliminate the fatty acid matrix interferences seen by the detectors. Likewise, the C-18 and SAX columns did little to eliminate matrix interferences. Using an acetone extraction followed by a PSA cleanup, both polar and nonpolar pesticides present in samples at 1.0 ng/g could be recovered.

Multiresidue pesticide analysis in fresh produce by capillary gas chromatography-mass spectrometry/selective ion monitoring (GC-MS/SIM) and -tandem mass spectrometry (GC-MS/MS).

A multiresidue method for the analysis of pesticides in fresh produce has been developed using salt-out acetonitrile extraction, solid-phase dispersive cleanup with octadecyl-bonded silica (C(18)), and graphitized carbon black/primary-secondary amine (GCB/PSA) sorbents and toluene, followed by capillary gas chromatography-mass spectrometry in selected ion monitoring mode (GC-MS/SIM) or -tandem mass spectrometry (GC-MS/MS). Quantitation was determined from calibration curves using matrix-matched standards ranging from 3.3 to 6667 ng/mL with r(2) > 0.99, and geometric mean limits of quantitation were typically 8.4 and 3.4 microg/kg for GC-MS/SIM and GC-MS/MS, respectively. Identification was determined by using target and qualifier ions and qualifier-to-target ratios for GC-MS/SIM and two ion transitions for GC-MS/MS. Fortification studies (10, 25, 100, and 500 microg/kg) were performed on 167 organohalogen, organophosphorus, and pyrethroid pesticides in 10 different commodities (apple, broccoli, carrot, onion, orange, pea, peach, potato, spinach, and tomato). The mean percent recoveries were 90 +/- 14, 87 +/- 14, 89 +/- 14, and 92 +/- 14% for GC-MS/SIM and 95 +/- 22, 93 +/- 14, 93 +/- 13, and 97 +/- 13% for GC-MS/MS at 10, 25, 100, and 500 microg/kg, respectively. GC-MS/MS was shown to be more effective than GC-MS/SIM due to its specificity and sensitivity in detecting pesticides in fresh produce samples. The method, based on concepts from the multiresidue procedure used by the Canadian Food Inspection Agency and QuEChERS (Quick, Easy, Cheap, Effective, Rugged, and Safe), was shown to be efficient in screening, identifying, and quantitating pesticides in fresh produce samples.

Multiresidue Pesticide Analysis of Ginseng Powders Using Acetonitrile- or Acetone-Based Extraction, Solid-Phase Extraction Cleanup, and Gas Chromatography−Mass Spectrometry/Selective Ion Monitoring (GC-MS/SIM) or −Tandem Mass Spectrometry (GC-MS/MS)†

A multiresidue method for the analysis of 168 pesticides in dried powdered ginseng has been developed using acetonitrile or acetone mixture (acetone/cyclohexane/ethyl acetate, 2:1:1 v/v/v) extraction, solid-phase extraction (SPE) cleanup with octyl-bonded silica (C(8)), graphitized carbon black/primary-secondary amine (GCB/PSA) sorbents and toluene, and capillary gas chromatography-mass spectrometry/selective ion monitoring (GC-MS/SIM) or -tandem mass spectrometry (GC-MS/MS). The geometric mean limits of quantitation (LOQs) were 53 and 6 microg/kg for the acetonitrile extraction and 48 and 7 microg/kg for the acetone-based extraction for GC-MS/SIM and GC-MS/MS, respectively. Mean percent recoveries and standard deviations from the ginseng fortified at 25, 100, and 500 microg/kg using GC-MS/SIM were 87 +/- 10, 88 +/- 8, and 86 +/- 10% from acetonitrile extracts and 88 +/- 13, 88 +/- 12, and 88 +/- 14% from acetone mixture extracts, respectively. The mean percent recoveries from the ginseng at the 25, 100, and 500 microg/kg levels using GC-MS/MS were 83 +/- 19, 90 +/- 13, and 89 +/- 11% from acetonitrile extracts and 98 +/- 20, 91 +/- 13, and 88 +/- 14% from acetone extracts, respectively. Twelve dried ginseng products were found to contain one or more of the following pesticides and their metabolites: BHCs (benzene hexachlorides, alpha-, beta-, gamma-, and delta-), chlorothalonil, chlorpyrifos, DDT (dichlorodiphenyl trichloroethane), dacthal, diazinon, iprodione, quintozene, and procymidone ranging from <1 to >4000 microg/kg. No significant differences were found between the two extraction solvents, and GC-MS/MS was found to be more specific and sensitive than GC-MS/SIM. The procedures described were shown to be effective in screening, identifying, confirming, and quantitating pesticides in commercial ginseng products.

Multiresidue Pesticide Analysis of Wines by Dispersive Solid-Phase Extraction and Ultrahigh-Performance Liquid Chromatography−Tandem Mass Spectrometry

A multiresidue pesticide method is described for the determination of 72 pesticides in wines. Pesticides were extracted using acetonitrile saturated with magnesium sulfate and sodium chloride, followed by solid-phase dispersive cleanup using primary-secondary amine and graphitized carbon black sorbents. Analysis is performed by ultraperformance liquid chromatography-electrospray ionization-tandem mass spectrometry (UPLC-MS/MS). The limits of quantitation (LOQs) for most of the pesticides ranged from 0.3 to 3.3 μg/L with the exception of cyromazine, fenhexamid, and acibenzolar S-methyl (LOQ > 10 μg/L), and quantitation was determined from calibration curves of standards containing 5.0-2500 μg/L with r(2) > 0.99. Recovery studies were performed by fortifying wine samples with the pesticides to concentrations of 10, 100, and 1000 μg/L, resulting in recoveries of >80% for most of the pesticides. Lower (<70%) and higher (>120%) recoveries were most likely from complications of pesticide lability or volatility, matrix interference, or inefficient desorption from the solid-phase sorbents. The method was used to analyze 10 wines collected from a market basket survey, and 19 different pesticides, primarily fungicides, were present at concentrations ranging from <1.0 to 1000 μg/L.

Assessing Children’s Dietary Pesticide Exposure: Direct Measurement of Pesticide Residues in 24-Hr Duplicate Food Samples

Background The data presented here are a response to calls for more direct measurements of pesticide residues in foods consumed by children and provide an opportunity to compare direct measures of pesticide residues in foods representing actual consumption with those reported by the U.S. Department of Agriculture Pesticide Data Program. Objective We measured pesticide residues in 24-hr duplicate food samples collected from a group of 46 young children participating in the Children’s Pesticide Exposure Study (CPES). Methods Parents were instructed to collect 24-hr duplicate food samples of all conventional fruits, vegetables, and fruit juices equal to the quantity consumed by their children, similarly prewashed/prepared, and from the same source or batch. Individual or composite food items were analyzed for organophosphate (OP) and pyrethroid insecticide residues. Results We collected a total of 239 24-hr duplicate food samples collected from the 46 CPES children. We found 14% or 5% of those food samples contained at least one OP or pyrethroid insecticide, respectively. We measured a total of 11 OP insecticides, at levels ranging from 1 to 387 ng/g, and three pyrethroid insecticides, at levels ranging from 2 to 1,133 ng/g, in children’s food samples. We found that many of the food items consumed by the CPES children were also on the list of the most contaminated food commodities reported by the Environmental Working Group. Conclusions The frequent consumption of food commodities with episodic presence of pesticide residues that are suspected to cause developmental and neurological effects in young children supports the need for further mitigation.

Assessing the consequences of the pesticide methoxychlor: neuroendocrine and behavioral measures as indicators of biological impact of an estrogenic environmental chemical

Japanese quail provide an advantageous avian model for assessing long-term biological consequences of endocrine disrupting chemicals (EDCs). These studies examined route of exposure and vulnerability to biological impact of EDCs over the life cycle in a precocial avian model, the Japanese quail. Embryonic exposure occurs with maternal deposition and methoxychlor (MXC) accumulated with maternal exposure. Egg injections of MXC or estradiol at selected stages of development impacted hypothalamic neuroendocrine systems in hatchlings and affected sexual maturation, with evidence for long-term effects on neurotransmitters and male behavior. Two-generation dietary studies were conducted to examine transgenerational effects of EDCs. Adult quail (P1) were exposed to dietary MXC (0, 0.5 and 5 ppm), with continued exposure in their offspring (F1), and control diet for all F2 chicks. Toxicological end points, including fertility, hatching success, and 14-day viability were unaffected. F1 and F2 male offspring from MXC-treated pairs MXC had impaired mating behavior and altered plasma hormones. These studies confirm neuroendocrine and behavioral measures as reliable indices of exposure to an estrogenic EDC. Moreover, maternal deposition remains a primary route of EDC exposure, with potential deleterious consequences for field birds, especially precocial species that appear to be particularly sensitive to embryonic EDC exposure.

Screening procedure for organochlorine and organophosphorus pesticide residues in milk using matrix solid phase dispersion (MSPD) extraction and gas chromatographic determination

A rapid technique for the extraction and gas chromatographic determination of five organochlorine and five organophosphorus pesticide residues in milk is described. Milk (5.0 ml) is blended with 2.0 g of C18 [octadecylsilyl-derivatized silica] and 1.5 ml acetonitrile in a syringe barrel. After the aqueous phase is removed from the column by vacuum aspiration, the pesticide residues are eluted from the C18/milk matrix with acetonitrile which is then eluted through a Florisil solid phase extraction (SPE) column. The acetonitrile is evaporated under nitrogen and the residue is dissolved in petroleum ether. This extract is directly analysed for organophosphorus pesticides by gas chromatography with flame photometric detection. After further clean-up of the extract on a mini-Florisil column, the organochlorine pesticide residues are determined by gas chromatography with electron capture detection. Grade A homogenized and raw milk samples were fortified with five organochlorine and five organophosphorus pesticide residues. The average recoveries of fortified organochlorine pesticide residues (2.0-20 ppb) ranged from 76.0% to 97.8%. The average recoveries of fortified organophosphorus pesticide residues (10-50 ppb) ranged from 75.0% to 104.5%. The MSPD and the AOAC International multiresidue method for pesticides in milk produced comparable results for milk samples containing incurred organochlorine pesticide residues. The use of the MSPD method results in a 90% reduction in organic solvent consumption and a 95% reduction in the hazardous waste generated when compared with the AOAC method.

Modeling Drug Residue Uptake by Eggs: Evidence of a Consistent Daily Pattern of Contaminant Transfer into Developing Preovulatory Yolks

A study was conducted to determine if the chicken ovary deposits the pesticide lindane into preovulatory egg yolks in a daily pattern similar to that previously reported for both of the antibiotics ampicillin and oxytetracycline. Our laboratory has proposed that a variety of drugs or contaminants are deposited into preovulatory yolks in a consistent manner. This possibility of a consistent pattern of drug deposition in preovulatory yolks has been used as a foundation for a model which predicts the pattern of residues contained in laid eggs. In two separate experiments, 16 hens were dosed with 3 mg of lindane per kg of body weight orally approximately 1 h after oviposition (8 hens per experiment). Twenty-four hours following dosing, hens were sacrificed and the ovaries were collected. Yolks were dissected free from the individual follicles with a blunt probe. Individual large (≥0.2 g) yellow yolks and a pool of 5 small (<0.2 g) yellow yolks were collected for determination of lindane content. Samples were prepared and assayed by using a gas chromatography method. Results indicate the pattern of incorporation of lindane residues in developing yolks is similar to the previous pattern obtained for both ampicillin and oxytetracycline. These data confirm the possibility that diverse chemical compounds may be incorporated into preovulatory yolks in a similar pattern, supporting a key component of our model, which predicts the pattern of incurred residues in laid eggs for a variety of drugs or contaminants.