Large volume cold on-column injection for gas chromatography-negative chemical ionization-mass spectrometry analysis of selected pesticides in air samples

A new gas chromatographic method is described for the analysis of fungicides captan, captafol, and folpet from organic extracts of air samples using large volume injection (LVI) via a cold on-column (COC) inlet coupled with gas chromatography-negative chemical ionization-mass spectrometry (GC-NCI-MS). Although standard split/splitless injection due to high injection port temperatures (>225 degrees C) have been shown to degrade these thermally labile fungicides, COC injection minimizes degradation. Insecticides such as chlorpyrifos and diazinon were also examined to show added selectivity. By using a solvent vapor exit with the COC inlet, injection volumes of 10-100 microL can be made to lower detection levels. GC-NCI-MS was compared to GC-electron impact ionization-mass spectrometry for each pesticide using LVI-COC injections and was found to be 2-80 times more sensitive, depending on the pesticide. Method detection limit (MDL) values with 100 microL injections were 2.5 microg L-1 for captan, folpet, and diazinon, 5.0 microg L-1 captafol, and 1.0 microg L-1 for chlorpyrifos, with the normal working range examined for sample analysis from MDL to 100 microg L-1. Detection of all pesticides except captafol, used only in the United States but not Canada, was demonstrated from air samples taken from Abbotsford, British Columbia, Canada.     

Residues of captan and folpet in strawberries and grapes

Fresh strawberries and grapes grown in Michigan and Indiana were surveyed for residues of captan and folpet, 2 fungicides commonly used on these crops. The fungicides were reportedly applied to the crops by overhead irrigation, tractor sprayer, or aerial spraying, in amounts ranging from 0.5 to 6 lb formulation/acre for captan and from 1 to 4 lb formulation/acre for folpet. Reported dates of last application ranged from just 2 days to nearly 5 months before samples were collected. Twenty-eight strawberry samples and 24 grape samples were collected of crops field-treated with one or both of these fungicides. Samples were analyzed by previously described methodology. Captan residues were found in all strawberry samples, ranging from less than 0.01 to 1.5 ppm. Folpet was found in only one strawberry sample at 0.041 ppm. Captan residues were found in only 6 grape samples, ranging from less than 0.01 to 0.082 ppm. Folpet residues were found in 12 grape samples, ranging from less than 0.01 to 0.50 ppm. All residues were well below the current tolerances of 25 ppm for both captan and folpet in strawberries and 50 ppm for captan and 25 ppm for folpet in grapes. Residue levels of these surface-applied, nonsystemic fungicides were inconsistent with amounts and dates of application, most likely because of variations in weather conditions, especially rainfall. Residues were quite stable in frozen sample homogenates, declining only 5-10% after 2 months.     

Gas-liquid chromatographic determination of captan and two metabolites in milk and meat

A gas-liquid chromatographic (GLC) method has been developed for the determination of captan (N-trichloromethylthio-4-cyclohexene-1,2-dicarboximide) and 2 metabolites, tetra-hydrophthalimide (THPI) and tetrahydrophthalamic acid (THPMA), in milk and meat. The sample is extracted with ethyl acetate and is cleaned up by acetonitrile partition and silica gel chromatography where captan, THPI, and THPMA are separated. Captan is directly determined by GLC. THPI and THPMA are separately derivatized in an acetone solution of pentafluorobenzyl bromide. The resultant derivatives are purified separately on an Al2O3 column and quantitated by GLC, using an electron capture detector. Recoveries from milk samples fortified at 0.02-10 ppm ranged from 71 to 102%; recoveries from meat samples fortified at 0.04-10 ppm ranged from 75 to 99%.     

The Luke et al. method for determining multipesticide residues in fruits and vegetables: collaborative study

Ten laboratories analyzed unfortified and fortified samples of lettuce, tomatoes, and strawberries for organochlorine and organophosphorus pesticides by applicable portions of the comprehensive multipesticide method of Luke et al. The 3 crops were fortified with 6 pesticides, alpha-BHC, dieldrin, chlorpyrifos, acephate, omethoate, and monocrotophos, each at 3 levels per crop. Included in the 54 fortifications were 16 pairs of blind duplicates: same pesticide, crop, and level. Recoveries were calculated by area comparisons with known reference materials, using the responses obtained from 2 separate element-specific gas chromatographic (GC) systems. The organochlorine pesticides were chromatographed on a methyl silicone column and detected with a Hall 700A electrolytic conductivity detector, and the organophosphorus pesticides were determined with a flame photometric detector after being chromatographed on a specified DEGS column material. Chlorpyrifos was quantitated on both GC systems. Mean recoveries ranged from 82.6% for acephate fortified at 0.5000 ppm in strawberries to 118.1% for 0.0636 ppm fortification of chlorpyrifos in lettuce. Interlaboratory coefficients of variation ranged from 4.0% for 0.6360 ppm fortification of chlorpyrifos in tomatoes to 17.8% for the 0.0636 ppm chlorpyrifos level in lettuce. The procedure features essentially no cleanup before GC and proved comparable to existing multiresidue methods for pesticides of the class types studied, as evidenced by the intra- and interlaboratory measurements of precision and recoveries obtained. The method with the 2 GC systems has been adopted official first action.     

Collaborative study of the determination of endosulfan, endosulfan sulfate, tetrasul, and tetradifon residues in fresh fruits and vegetables.

A method for the determination of endosulfan I, endosulfan II, endosulfan sulfate, tetrasul, and tetradifon residues in fresh fruits and vegetables was studied collaboratively. The method consists of extraction of the product with acetonitrile, ether and elution from a Florisil column with mixtures of hexane, methylene chloride, and acetonitrile, and determination of the residues by electron capture gas-liquid chromatography. This method was studied by 8 collaborators, using apples and cucumbers as the samples. Each sample was spiked with 2 levels of each pesticide. The average per cent recoveries for apples and cucumbers, respectively were as follows: endosulfan I, 103.6 and 101.5; endosulfan II, 102.9 and 100.0; endosulfan sulfate, 100.9 and 92.9; tetrasul, 98.8 and 102.2; and tetradifon, 106.4 and 101.9. The method has been adopted as official first action.     

Determination of quinomethionate (6-methylquinoline-2,3-diyldithiocarbonate) residues in crops by in situ fluorometry.

A simple method is described for the quantitative determination of quinomethionate (6-methylquinoline- 2,3 - diyldithiocarbonate) in crops. The pesticide residue is extracted with acetonitrile and partitioned in petroleum ether. After separation from the co-extractives by thin layer chromatography (TLC), the fluorescence is measured directly on a silica gel TLC plate. An average of 89% recovery is obtained at the 0.05 ppm level in apples, peaches, pears, and tomatoes.     

Gas chromatographic determination of mecarbam and its metabolites mecarboxon, diethoate, and diethoxon in cottonseeds

A gas chromatographic method is described for determining residues of mecarbam and 3 of its metabolites, mecarboxon, diethoate, and diethoxon, in cottonseeds. For mecarbam analysis, following Soxhlet extraction with chloroform (after blending), the oily extract is partitioned with propylene carbonate and cleaned up on a silica gel column. Metabolites are extracted by the same method, followed by cleanup of mecarboxon on a silica gel column or diethoxon on an alumina column; cleanup of diethoate can be performed on either column. All 4 compounds are determined using a flame photometric detector equipped with a phosphorus filter. Average recoveries for cottonseed samples fortified with 0.03-1.0 ppm mecarbam ranged from 80 to 88%. Average recoveries were 81-88% for mecarboxon and 90-92% for diethoate (alumina column) and diethoxon from samples fortified with 0.05-1.0 ppm. Average recovery of diethoate from samples cleaned up on the silica gel column were 84-88% in the range of 0.05-0.2 ppm. Values obtained for mecarbam residues in field-treated samples are also presented.     

Determination of daminozide in apples by gas chromatography/chemical ionization mass spectrometry

A method using gas chromatography/chemical ionization mass spectrometry (GC/CIMS) for the determination of daminozide residues in apples has been developed. Daminozide was separated from the sample matrix by water extraction and cation exchange, converted to the methyl ester by treatment with HCl-methanol, and determined by GC/CIMS using succinonitrile as an internal standard. The detection level was 0.05 ppm. Recoveries were 92-104% from apples spiked at the 0.05-0.5 ppm levels. Of the 25 apple samples analyzed, only 2 were positive for daminozide (1.04 and 0.32 ppm).     

High pressure liquid chromatographic determination of naphthaleneacetic acid residues in apples.

An ion-suppression reverse phase high pressure liquid chromatographic method is described for determining naphthaleneacetic acid (NAA) residues in apples. Samples are extracted with acidic chloroform, filtered through pre-acidified Hy-Flo Supercel, and cleaned up by acid-base partitioning. The extract can be successfully chromatographed on either a muLiChrosorb NH2 or muBondapak C18 column and quantitated by using a variable wavelength ultraviolet detector set at 220 nm. The mobile phase is acetonitrile-water (20 + 80) buffered to pH 3.5 (MULiChrosorb column) or pH 5.2 (MUBondapak column) and flowing at 1.0--2.0 ml/min. Recoveries ranged from 86 to 98%. The minimum detectable amount was 0.5 ng, which easily permitted the quantitation of 0.01 ppm NAA in 50 g sample. A fluorometric detector was 4 times as sensitive, using an excitation wavelength of 220 mm and monitoring the emission at 340 nm. For this detector, the minimum detectable amount was 0.12 ng NAA.     

Gas chromatographic determination of pentachlorophenol in gelatin: collaborative study

Eleven collaborators participated in this study of a gas chromatographic method for the determination of pentachlorophenol (PCP) in gelatin. Following acid hydrolysis of a 2 g sample, PCP is extracted with hexane and partitioned into KOH solution. After reacidification, PCP is again extracted with hexane for determination by electron capture gas chromatography on a 1% SP-1240DA column. Three duplicate practice samples (0.0, 0.5, and 1.5 ppm) and 5 blind duplicate collaborative samples (0.0, 0.02, 0.1, 0.5, and 2.0 ppm) were analyzed by each collaborator. Mean recoveries of PCP in the collaborative samples ranged from 88% at the 0.02 ppm fortification level to 102% at the 0.1 ppm level; the overall mean recovery was 96%. Interlaboratory coefficients of variation ranged from 16.4% for the 0.1 ppm fortification level to 22.9% for the 0.5 ppm level; the overall interlaboratory coefficient of variation was 19.5%. The method has been adopted official first action.     

Analysis of fenhexamid in caneberry, blueberry, and pomegranate by liquid chromatography-tandem mass spectrometry

An analytical method for the determination of fenhexamid [N-(2,3-dichloro-4-hydroxyphenyl)-1-methylcyclohexanecarboxamide] in caneberry, blueberry, and pomegranate was developed utilizing acetone extraction, column cleanup, liquid-liquid partitioning, and liquid chromatography-tandem mass spectroscopy (LC-MS/MS) for detection. Method validation recoveries ranged from 91 to 96% for caneberry, from 80 to 91% for blueberry, and from 74 to 95% for pomegranate. Control samples collected from IR-4 trials for all matrixes had residue levels of <0.020 ppm. Fenhexamid-treated field samples had residue levels that ranged from 0.46 to 16.11 ppm (caneberry), from 0.87 to 2.91 ppm (blueberry), and from 1.59 to 1.85 ppm (pomegranate). The method was validated to a limit of quantitation of 0.020 ppm, and the limit of detection was 0.009 ppm.     

U.S. market basket study to determine residues of the insecticide chlorpyrifos.

A market basket study was conducted to measure residues of the insecticide chlorpyrifos in samples of apples, applesauce, apple juice, fresh orange juice, tomatoes, peanut butter, whole milk, ground beef, and pork sausage collected during a 12-month period from 200 grocery stores across the United States. Approximately 90% of the samples contained no detectable levels of chlorpyrifos, and all residues detected were below tolerances, the legal limits for the United States. No values greater than the limit of quantitation (LOQ) were found in applesauce (LOQ = 0.008 ppm), apple juice (LOQ = 0.003 ppm), whole milk (LOQ = 0.006 ppm), ground beef (LOQ = 0.005 ppm), or pork sausage (LOQ = 0.007 ppm) samples. Only one fresh orange juice sample contained residues greater than the LOQ at 0.015 ppm. Only about 20% of the apples (maximum = 0.052 ppm), 20% of the tomato samples (maximum = 0.058 ppm), and 50% of the peanut butter samples (maximum = 0.021 ppm) contained quantifiable residues.     

Residue analysis of glyphosate and its principal metabolite in certain cereals, oilseeds, and pulses by liquid chromatography and postcolumn fluorescence detection.

A postcolumn liquid chromatographic method to determine the extractable residues of glyphosate (GLYPH) and its principal metabolite, (aminomethyl)phosphonic acid (AMPA), in various cereals and beans is described. The finely ground sample is extracted with a mixture of chloroform and water, and the resulting aqueous layer is passed through a cation exchange column. The eluate is adjusted to pH 7-10 and passed through an anion exchange column. The second column is eluted with 0.3M HCl solution and the resulting acidic eluate is analyzed with liquid chromatography coupled with postcolumn fluorescence detection. The mean recoveries for GLYPH in barley, canola, dry pea, flax, soybean, wheat, and white bean ranged from 90.0 to 98.1%, with coefficients of variation (CV) from 2.9 to 10.0% and limits of detection (LOD) from 0.07 to 0.14 ppm. Similarly, mean recoveries for AMPA in the same crops ranged from 87.4 to 98.9%, with CV from 4.6 to 7.7 and LOD from 0.05 to 0.12 ppm. Using this method, an analyst can routinely analyze 6 samples per 1.5 days. The advantages of this procedure are discussed.     

High-speed liquid chromatographic determination of monensin, narasin, and salinomycin in feeds, using post-column derivatization

A high-speed liquid chromatographic (LC) method using post-column derivatization is described for the determination of monensin, narasin, and salinomycin in a variety of animal feeds. The ionophores are extracted with hexane-ethyl acetate (90 + 10). A portion of the sample is evaporated, diluted to a known volume, and analyzed using a 6 cm 3 microns C18 column and an absorbance detector after post-column reaction with vanillin. The method has been applied to poultry and swine feeds with levels of 3-100 ppm added antibiotic. A comparison was also carried out with medicated poultry feed and beef feed lot supplement samples previously analyzed by 2 separate bioassay methods for monensin and salinomycin, respectively. Recoveries for the LC method ranged from 92.1 to 103% with an average recovery of 98.1% and a coefficient of variation of 3.65%.     

The effect of ph on fungitoxic interactions between a solvent and pesticide

The effect of pH on interactions between combinations of the solvent acetone and the pesticide captan was determined using the fungiPythium ultimum, Sclerotinia homeocarpa, andPestalotia sp.. Seven concentrations of the solvent acetone, ranging from 0.1 to 3.0 % (v/v), were interacted with four concentrations of the fungicide captan, ranging from 1.0 to 10.0 ppm (mg L^?1). This interaction procedure was repeated at pH 4.5, 5.5, 6.5, and 7.5, using a temperature of 30 °C. Acetone and captan interacted synergistically towardsP. ultimum andS. homeocarpa, and antagonistically towardsPestalotia sp., regardless of the pH. However, the solvent concentration at which synergism or antagonism was first observed usually decreased as pH increased. The actual pH response obtained was dependent upon both the captan level and culture used. As pH increased from 4.5 to 7.5, the toxicity of captan decreased by up to 40% withS. homeocarpa andPestalotia sp., and 80% withP. ultimum. WithS. homeocarpa andPestalotia sp., the magnitude of synergism or antagonism increased as the captan concentration was raised from 1.0 or 2.5 ppm up to 7.5 or 10.0 ppm. With P. ultimum, the degree of synergism decreased at pH 4.5 and 5.5, but increased at pH 6.5 and 7.5, as the captan concentration was raised from 2.5 to 10.0 ppm. The lowest interaction magnitudes were recorded at pH 4.5 forP. ultimum, but was variable for the other cultures. The greatest interaction magnitudes were obtained at pH 4.5 forS. homeocarpa, 5.5 forPestalotia sp., and 6.5 or 7.5 forP. ultimum.     

Quantitation of o- and p-sulfamoylbenzoic acids in commerical saccharin by high-performance liquid chromatography.

Quantitation of o- and p-sulfamoylbenzoic acid residues in saccharin and its sodium salt is achieved by a method comprising methanolic extraction and high-performance ion exchange chromatography. A commercially available anion exchange column was employed with an aqueous buffered (pH 9.2) mobile phase. As little as 80 ppm of the ortho-isomer and 25 ppm of the para-isomer can be accurately determined. The levels of detectability (2 times noise) are estimated as 8 ppm (0.16 mug on column) and 2.5 ppm (0.05 mug on column), respectively. Recoveries from saccharin ranged from 92.7 to 96.5% (ortho) and from 92.2 to 103.3% (para). Recoveries from the sodium salt ranged from 93.1 to 104.4% (ortho) and from 93.5 to 97.8% (para). Of 9 other potential saccharin impurities tested separately, only one was found to interfere slightly in the chromatographic part of the procedure.     

Postharvest treatments for the reduction of mancozeb in fresh apples.

The objective of this study was to determine the effectiveness of chlorine, chlorine dioxide, ozone, and hydrogen peroxyacetic acid (HPA) treatments on the degradation of mancozeb and ethylenethiourea (ETU) in apples. This study was based on model experiments at neutral pH and temperature. Fresh apples were treated with two different levels of mancozeb (1 and 10 microg/mL). Several of the treatments were effective in reducing or removing mancozeb and ETU residues on spiked apples. Mancozeb residues decreased 56-99% with chlorine and 36-87% with chlorine dioxide treatments. ETU was completely degraded by 500 ppm of calcium hypochlorite and 10 ppm of chlorine dioxide at a 1 ppm spike level. However, at a 10 ppm spike level, the effectiveness of ETU degradation was lower than observed at 1 ppm level. Mancozeb residues decreased 56-97% with ozone treatment. At 1 and 3 ppm of ozone, no ETU residue was detected at 1 ppm of spiked mancozeb after both 3 and 30 min. HPA was also effective in degrading the mancozeb residues, with 44-99% reduction depending on treatment time and HPA concentrations. ETU was completely degraded at 500 ppm of HPA after 30 min of reaction time. These treatments indicated good potential for the removal of pesticide residues on fruit and in processed products.     

Liquid chromatographic determination of N-methylcarbamate insecticides and metabolites in crops. I. Collaborative study

A liquid chromatographic (LC) multiresidue method for determining residues of N-methylcarbamate insecticides in crops was collaboratively studied in 6 laboratories. Methanol and a mechanical ultrasonic homogenizer are used to extract the carbamates. Water-soluble plant coextractives and nonpolar plant lipid materials are removed from the carbamate residues by liquid-liquid partitioning. Additional crop coextractives (e.g., carotenes, chlorophylls) are removed with a Nuchar SN-silanized Celite column. The carbamate residues are then separated on a reverse phase LC column, using an acetonitrile-water gradient mobile phase. Eluted residues are detected by an in-line post-column fluorometric detection technique. Seven carbamates and 2 carbamate metabolites were included in the collaborative study. Each collaborator determined all the carbamates at 2 levels (approximately 0.05 ppm and United States tolerance) in blind duplicate samples of grapes and potatoes. Fortified and control samples were analyzed. Repeatability coefficients of variation for all the carbamates on the 2 crops averaged 4.7% and ranged from 2.4 to 7.1%. Reproducibility coefficients of variation for all the carbamates on the 2 crops averaged 8.7% and ranged from 5.3 to 12.4%. Accuracy, measured by comparison with fortification values, averaged 95% and ranged from 79 to 103%. The estimated limit of quantitation is 0.01 ppm. The method has been adopted official first action.     

Liquid chromatographic determination of multiresidue fluorescent derivatives of ionophore compounds, monensin, salinomycin, narasin, and lasalocid, in beef liver tissue

A liquid chromatographic (LC) method with fluorometric detection was developed to quantitatively determine residue levels of monensin, salinomycin, narasin, and lasalocid in beef liver tissue. The ionophores are extracted from the tissue, purified by both alumina and Sephadex LH-20 column chromatography, and then derivatized. Lasalocid was directly esterified with 9-anthryldiazomethane (ADAM), but monensin, salinomycin, and narasin were first acetylated with acetic anhydride and then esterified with ADAM. The ADAM derivatives were purified on a silica gel column and separated by LC using an RP C-8 5 micron column. A fluorescence detector set at 365 nm (excitation) and 418 nm (emission) was used to monitor the column effluent. The detection limits were 0.15 ppm, and the calibration curves were linear between 0.5 and 5.0 ppm for all 4 ionophores. Mean recoveries were 57, 70, 75, and 90% for lasalocid (5 ppm), monensin (2.5 ppm), salinomycin (2.5 ppm), and narasin (2.5 ppm), respectively. The ionophores were also separated and semiquantitated by using bioautography and thin layer chromatography with a vanillin spray.     

Determination of polybrominated biphenyl residues in dairy products.

A method for the determination of polybrominated biphenyls (PBBs) in dairy products is described. Fat is extracted from the products by the official AOAC method. The PBB residues are separated from the fatty material by gel permeation chromatography prior to gas-liquid chromatographic (GLC) quantitation. An additional cleanup using petroleum ether elution through a miniature Florisil column is necessary for thin layer chromatographic (TLC) confirmation. Recoveries of PBBs from samples fortified at levels from 0.1 to 0.5 ppm ranged from 94 to 104% with an average of 99%. GLC sensitivity permits the estimation of PBB residue levels as low as 0.007 ppm. Routine TLC confirmation is limited by sensitivity to greater than or equal to 0.2 ppm.