Microwave-Assisted Extraction Coupled with Gas Chromatography with Nitrogen-Phosphorus Detection or Electron Capture Negative Chemical Ionization Mass Spectrometry for Determination of Dimethomorph Residues in Soil

Dimethomorph, a cinnamic acid derivative, is a crop protection product for the control of fungi in grapes, tomatoes, potatoes, and tobacco. Of the extraction techniques evaluated, microwave-assisted extraction (MAE) gave the best extractability of the analyte at trace levels from soil. After an appropriate cleanup, dimethomorph residues could be determined by gas chromatography (GC) with either nitrogen-phosphorus detection (NPD) or mass spectrometry with electron capture negative chemical ionization (ECNCI). The sensitivity and specificity of the latter detection technique made it possible to use a greatly simplified cleanup procedure. The limit of quantitation of both procedures was 10 ppb. Soils fortified over a range of 10 to 500 ppb gave an average recovery of 88%, with a standard deviation of 11% by GC-NPD and an average recovery of 99%, with a standard deviation of 8.8% by GC/ECNCI. Control soils generally showed apparent residues of less than 1 ppb

Determination of Hydramethylnon Residues in Grass by Liquid Chromatography with Confirmation by Liquid Chromatography/Mass Spectrometry

An improved method for determination of hydra-methylnon residues in pasture grass is described. The method uses (1) the hydrochloride salt of hy-dramethylnon to improve its water solubility and (2) an acid–methanol precipitation to remove chlorophylls while leaving the analyte in solution. The liquid chromatographic method has a validated sensitivity of 0.05 ppm with controls showing <0.004 ppm. The overall average recovery from 0.05 to 0.50 ppm was 98%, with a standard deviation of 11%. Samples showing a positive response (0.05 ppm or higher) and requiring mass spectrometric confirmation are directly amenable to liquid chromatography/mass spectrometry without additional sample preparation.

Liquid Chromatographic Determination of Moxidectin Residues in Cattle Tissues and Confirmation in Cattle Fat by Liquid Chromatography/Mass Spectrometry

Moxidectin, a potent new endo- and ectoparasitic agent, is determined in cattle tissues by liquid chromatography (LC) with fluorescence detection. Moxidectin residues in cattle fat are confirmed with thermospray LC/mass spectrometry (MS). Moxidectin is extracted from the tissue with acetonitrile; the extract is partitioned with hexane, concentrated, and reacted with acetic anhydride, 1-methylimidazole, and dimethylformamide to produce a fluorescent product. The validated sensitivity of the LC/fluorescence method was 10 ppb, with a limit of detection typically between 1 and 2 ppb. Average recoveries from cattle fat, muscle, liver, and kidney were 99,95,89, and 92%, respectively. LC/MS confirmatory method determined the underivatized parent compound following the acetonitrilehexane partitioning step, with an average recovery of 108% at the 250 ppb level in cattle fat.

Rapid Determination of Imazapyr in Corn by Gas Chromatography/Mass Spectrometry with Electron Capture Negative Ion Chemical Ionization

Imazapyr, an imidazolinone class herbicide, was developed recently for weed control in imidazolinonetolerant corn. Current methods for determining imidazolinone herbicides in crops involve laborious, time-consuming cleanup procedures after extraction. We developed an extremely simple cleanup procedure for imazapyr in corn commodities after extraction with acidic acetone-water by using gas chromatography/mass spectrometry with electron capture negative ion chemical ionization for final detection. Method sensitivity was 50 ppb, with controls showing <5 ppb. Average recoveries from corn forage, fodder, and grain were 98,106, and 101%, respectively.

Simplified Determination of Imidazolinone Herbicides in Soil at Parts-per-Billion Level by Liquid Chromatography/ Electrospray Ionization Tandem Mass Spectrometry

Imidazolinones are a significant new class of low-use-rate, reduced-environmental-risk herbicides for protection of a wide variety of agricultural commodities. Because of their low rates of application, residues of imidazolinones in soil need to be monitored at low parts-per-billion (ppb) levels. Greatly simplified cleanup procedures were reported recently for determining imidazolinones in soil at the 1 ppb level by combining microwave-assisted extraction (MAE) with gas chromatography/electron capture negative chemical ionization mass spectrometry (GC/ECNCI) and for determining imidazolinones in water by using liquid chromatography/electrospray ionization mass spectrometry (LC/ESMS) and liquid chromatography/electrospray ionization tandem MS (LC/ESMS/MS). By merging the extraction and cleanup procedures for determining imidazolinones in soil with LC/ESMS/MS, instrumental analysis time was reduced to that approximating sample preparation time, and the drawbacks of in situ methylation required for GC/ECNCI were eliminated. Recoveries of imazethapyr, the most widely used imidazolinone, from a variety of soil types fortified at 1–50 ppb averaged 92% with a standard deviation of 9.7%. Control soil extracts gave apparent residues of <0.2 ppb. These results were almost identical to those previously reported for GC/ECNCI.

Simplification of Analytical Methods in Pesticide Residue Analysis by Liquid Chromatography/Electrospray Ionization Mass Spectrometry and Tandem Mass Spectrometry

This report presents a historic, scientific, and economic overview of why mass spectrometry (MS) is rapidly becoming a routine detector for trace analysis of pesticide residues in the regulatory area. Liquid chromatography/electrospray ionization MS and tandem MS dramatically simplify cleanup procedures, reducing not only sample analysis time, but even more important, method development time. Examples include direct determination of imidazolinones in water at 1 ppb, determination of imazethapyr and its metabolites in crop commodities, and determination of imazethapyr in soil.

Multiresidue Determination and Confirmation of Imidazolinone Herbicides in Soil by High-Performance Liquid Chromatography/Electrospray Ionization Mass Spectrometry

A new multiresidue method was developed to determine 6 imidazolinone herbicides in 5 different soil types, using high-performance liquid chromatography/electrospray ionization mass spectrometry (HPLC/ESMS). Good recoveries and sensitivity were obtained for the compounds investigated at the 2.0 ppb limit of quantitation. A 50 g portion of soil was extracted with 0.5N NaOH. A portion of the extract was acidified to precipitate humic acids, and the supernatant was loaded onto a preconditioned tC-18 solid-phase extraction (SPE) cartridge and eluted with ethyl acetate. Further cleanup was achieved by using a tandem strong-anion-ex- change SPE/strong-cation-exchange (SCX) SPE. Analytes were eluted from the SCX SPE with saturated KCI in methanol. After cleanup, the sample was desalted with an RP-102 SPE cartridge. Quantitation was achieved by monitoring the [M + H]+ ions for each compound, with a time-scheduled selective-ion-monitoring program (positive mode). The extraction and cleanup procedure produced a purified extract for MS confirmation using 3 ions with “in-source” collision-induced dissociation.

Confirmation of Moxidectin Residues in Cattle Fat by Liquid Chromatography/Mass Spectrometry

Moxidectin, a potent new endo- and ectoparasitic agent, is determined in cattle tissues by liquid chromatography (LC) with fluorescence detection. The original confirmatory method for moxidectin in cattle fat, the target tissue for regulatory purposes, was LC with mass spectrometry (MS) using thermospray (TSP) ionization and selected ion monitoring. As newer ionization techniques for LC/MS made TSP obsolete and with the availability of a new generation of benchtop LC/MS instrumentation, the confirmation of moxidectin in cattle fat was re-evaluated. The ionization techniques of atmospheric pressure chemical ionization versus electrospray ionization, the detection techniques of single-stage MS versus tandem MS, and the instrumentation of ion trap versus quadrupole were investigated. The final confirmatory method was based on full-scan single-stage MS. Even with full-scan detection, the analysis required at least 10-fold less extract than the original TSP method. The applicability of this new confirmatory method was demonstrated on both ion trap and quadrupole instruments.

DGAT2 Inhibition Alters Aspects of Triglyceride Metabolism in Rodents but Not in Non-human Primates

Diacylglycerol acyltransferase 2 (DGAT2) catalyzes the final step in triglyceride (TG) synthesis and has been shown to play a role in regulating hepatic very-low-density lipoprotein (VLDL) production in rodents. To explore the potential of DGAT2 as a therapeutic target for the treatment of dyslipidemia, we tested the effects of small-molecule inhibitors and gene silencing both in vitro and in vivo. Consistent with prior reports, chronic inhibition of DGAT2 in a murine model of obesity led to correction of multiple lipid parameters. In contrast, experiments in primary human, rhesus, and cynomolgus hepatocytes demonstrated that selective inhibition of DGAT2 has only a modest effect. Acute and chronic inhibition of DGAT2 in rhesus primates recapitulated the in vitro data yielding no significant effects on production of plasma TG or VLDL apolipoprotein B. These results call into question whether selective inhibition of DGAT2 is sufficient for remediation of dyslipidemia.

Dose-dependent effects of siRNA-mediated inhibition of SCAP on PCSK9, LDLR, and plasma lipids in mouse and rhesus monkey

SREBP cleavage-activating protein (SCAP) is a key protein in the regulation of lipid metabolism and a potential target for treatment of dyslipidemia. SCAP is required for activation of the transcription factors SREBP-1 and -2. SREBPs regulate the expression of genes involved in fatty acid and cholesterol biosynthesis, and LDL-C clearance through the regulation of LDL receptor (LDLR) and PCSK9 expression. To further test the potential of SCAP as a novel target for treatment of dyslipidemia, we used siRNAs to inhibit hepatic SCAP expression and assess the effect on PCSK9, LDLR, and lipids in mice and rhesus monkeys. In mice, robust liver Scap mRNA knockdown (KD) was achieved, accompanied by dose-dependent reduction in SREBP-regulated gene expression, de novo lipogenesis, and plasma PCSK9 and lipids. In rhesus monkeys, over 90% SCAP mRNA KD was achieved resulting in approximately 75, 50, and 50% reduction of plasma PCSK9, TG, and LDL-C, respectively. Inhibition of SCAP function was demonstrated by reduced expression of SREBP-regulated genes and de novo lipogenesis. In conclusion, siRNA-mediated inhibition of SCAP resulted in a significant reduction in circulating PCSK9 and LDL-C in rodent and primate models supporting SCAP as a novel target for the treatment of dyslipidemia.

Evaluation of CETP activity in vivo under non-steady-state conditions: influence of anacetrapib on HDL-TG flux

Studies in lipoprotein kinetics almost exclusively rely on steady-state approaches to modeling. Herein, we have used a non-steady-state experimental design to examine the role of cholesteryl ester transfer protein (CETP) in mediating HDL-TG flux in vivo in rhesus macaques, and therefore, we developed an alternative strategy to model the data. Two isotopomers ([(2)H11] and [(13)C18]) of oleic acid were administered (orally and intravenously, respectively) to serve as precursors for labeling TGs in apoB-containing lipoproteins. The flux of a specific TG (52:2) from these donor lipoproteins to HDL was used as the measure of CETP activity; calculations are also presented to estimate total HDL-TG flux. Based on our data, we estimate that the peak total postprandial TG flux to HDL via CETP is ∼ 13 mg · h(-1) · kg(-1) and show that this transfer was inhibited by 97% following anacetrapib treatment. Collectively, these data demonstrate that HDL TG flux can be used as a measure of CETP activity in vivo. The fact that the donor lipoproteins can be labeled in situ using well-established stable isotope tracer techniques suggests ways to measure this activity for native lipoproteins in free-living subjects under any physiological conditions.

Potential mechanism of enhanced postprandial glucagon-like peptide-1 release following treatment with a diacylglycerol acyltransferase 1 inhibitor

Studies have demonstrated that blockade of diacylglycerol acyltransferase 1 (DGAT1) leads to prolonged release of glucagon‐like peptide 1 (GLP‐1) after meal challenge. The current study was undertaken to investigate the mechanism of action underlying the elevated levels of GLP‐1 release following pharmacological inhibition of DGAT1. We utilized a potent, specific DGAT1 inhibitor, compound A, to investigate the changes in intestinal lipid profile in a mouse model after oral administration of the compound and challenge with tracer containing fatty meal. [¹³C₁₈]‐oleic acid and LC‐MS were employed to trace the fate of dietary fatty acids provided as part of a meal challenge in lean mice. Lipid profiles in plasma, proximal to distal segments of intestine, and feces were evaluated at various times following the meal challenge to study the kinetics of fatty acid absorption, synthesis into complex lipids, and excretion. Pharmacological inhibition of DGAT1 led to reduction of postprandial total and newly synthesized triglyceride (TG) excursion and significant increases in TG and FFA levels in the distal portion of intestine enriched with enteroendocrine L cells. Enhanced levels of FFA and cholesteryl ester were observed via fecal fat profiling. DGAT1 inhibition leads to enhancement of carbon flow to the synthesis of phosphatidylcholine within the intestine. DGAT1 inhibition markedly increases levels of TG and FFA in the distal intestine, which could be the predominant contributor to the prolonged and enhanced postprandial GLP‐1 release. Inactivation of DGAT1 could provide potential benefit in the treatment of dysmetabolic diseases.

Discovery and Pharmacology of a Novel Class of Diacylglycerol Acyltransferase 2 Inhibitors

DGAT2 plays a critical role in hepatic triglyceride production, and data suggests that inhibition of DGAT2 could prove to be beneficial in treating a number of disease states. This article documents the discovery and optimization of a selective small molecule inhibitor of DGAT2 as well as pharmacological proof of biology in a mouse model of triglyceride production.

Discovery of Novel Allosteric Non-Bisphosphonate Inhibitors of Farnesyl Pyrophosphate Synthase by Integrated Lead Finding

Farnesyl pyrophosphate synthase (FPPS) is an established target for the treatment of bone diseases, but also shows promise as an anticancer and anti-infective drug target. Currently available anti-FPPS drugs are active-site-directed bisphosphonate inhibitors, the peculiar pharmacological profile of which is inadequate for therapeutic indications beyond bone diseases. The recent discovery of an allosteric binding site has paved the way toward the development of novel non-bisphosphonate FPPS inhibitors with broader therapeutic potential, notably as immunomodulators in oncology. Herein we report the discovery, by an integrated lead finding approach, of two new chemical classes of allosteric FPPS inhibitors that belong to the salicylic acid and quinoline chemotypes. We present their synthesis, biochemical and cellular activities, structure-activity relationships, and provide X-ray structures of several representative FPPS complexes. These novel allosteric FPPS inhibitors are devoid of any affinity for bone mineral and could serve as leads to evaluate their potential in none-bone diseases.

Effect of Error Propagation in Stable Isotope Tracer Studies: An Approach for Estimating Impact on Apparent Biochemical Flux

Stable isotope tracers are widely used to quantify metabolic rates, and yet a limited number of studies have considered the impact of analytical error on estimates of flux. For example, when estimating the contribution of de novo lipogenesis, one typically measures a minimum of four isotope ratios, i.e., the precursor and product labeling pre- and posttracer administration. This seemingly simple problem has 1 correct solution and 80 erroneous outcomes. In this report, we outline a methodology for evaluating the effect of error propagation on apparent physiological endpoints. We demonstrate examples of how to evaluate the influence of analytical error in case studies concerning lipid and protein synthesis; we have focused on (2)H2O as a tracer and contrast different mass spectrometry platforms including GC-quadrupole-MS, GC-pyrolysis-IRMS, LC-quadrupole-MS, and high-resolution FT-ICR-MS. The method outlined herein can be used to determine how to minimize variations in the apparent biology by altering the dose and/or the type of tracer. Likewise, one can facilitate biological studies by estimating the reduction in the noise of an outcome that is expected for a given increase in the number of replicate injections.

Use of [13C18] oleic acid and mass isotopomer distribution analysis to study synthesis of plasma triglycerides in vivo: analytical and experimental considerations

We have previously reported on a liquid chromatography-mass spectrometry method to determine the disposition of [(13)C18]-oleic acid following intravenous and oral administration in vivo. This approach has enabled us to study a variety of aspects of lipid metabolism including a quantitative assessment of triglyceride synthesis. Here we present a more rigorous evaluation of the constraints imposed upon the analytical method in order to generate accurate data using this stable-isotope tracer approach along with more detail on relevant analytical figures of merit including limits of quantitation, precision, and accuracy. The use of mass isotopomer distribution analysis (MIDA) to quantify plasma triglyceride synthesis is specifically highlighted, and a re-evaluation of the underlying mathematics has enabled us to present a simplified series of equations. The derivation of this MIDA model and the significance of all underlying assumptions are explored in detail, and examples are given of how it can successfully be applied to detect differences in plasma triglyceride synthesis in lean and high-fat diet fed mouse models. More work is necessary to evaluate the applicability of this approach to triglyceride stores with slower rates of turnover such as in adipose or muscle tissue; however, the present report provides investigators with the tools necessary to conduct such studies.

New methodologies for studying lipid synthesis and turnover: looking backwards to enable moving forwards

Our ability to understand the pathogenesis of problems surrounding lipid accretion requires attention towards quantifying lipid kinetics. In addition, studies of metabolic flux should also help unravel mechanisms that lead to imbalances in inter-organ lipid trafficking which contribute to dyslipidemia and/or peripheral lipid accumulation (e.g. hepatic fat deposits). This review aims to outline the development and use of novel methods for studying lipid kinetics in vivo. Although our focus is directed towards some of the approaches that are currently reported in the literature, we include a discussion of the older literature in order to put "new" methods in better perspective and inform readers of valuable historical research. Presumably, future advances in understanding lipid dynamics will benefit from a careful consideration of the past efforts, where possible we have tried to identify seminal papers or those that provide clear data to emphasize essential points. This article is part of a Special Issue entitled: Modulation of Adipose Tissue in Health and Disease.

Tracking fatty acid kinetics in distinct lipoprotein fractions in vivo: a novel high-throughput approach for studying dyslipidemia in rodent models

Isotopic tracers have been used to examine lipid trafficking for many years, and data from those studies have typically yielded novel insight regarding the pathophysiology of dyslipidemia. Previous experimental designs were suitable for studies in humans because relatively large volumes of plasma could be regularly sampled. We have expanded on the earlier logic by applying high-throughput analytical methods that require reduced sample volumes. Specifically, we have examined the possibility of coupling gel-based separations of lipoproteins (e.g., lipoprint) with LC-MS/MS analyses of complex lipid mixtures as a way to routinely measure the labeling profiles of distinct lipids in discrete lipoprotein subfractions. We demonstrate the ability to measure the incorporation of [U-(13)C]oleate into triglycerides (TG), PLs (PL), and cholesterol esters (CE) in VLDL, LDL, and HDL particles in mice. Although rodent models of dyslipidemia are inherently different from humans because of alterations in enzyme activities and underlying metabolism, rodent models can be used to screen novel compounds for efficacy in altering a given biochemical pathway and therein enable studies of target engagement in vivo. We expect that it is possible to translate our approach for application in other systems, including studies in humans.

Mass Spectrometric Techniques for Label-free High-Throughput Screening in Drug Discovery

High-throughput screening (HTS) is an important tool for finding active compounds to initiate medicinal chemistry programs in pharmaceutical discovery research. Traditional HTS methods rely on fluorescent or radiolabeled reagents and/or coupling assays to permit quantitation of enzymatic target inhibition or activation. Mass spectrometry-based high-throughput screening (MS-HTS) is an alternative that is not susceptible to the limitations imposed by labeling and coupling enzymes. MS-HTS offers a selective and sensitive analytical method for unlabeled substrates and products. Furthermore, method development times are reduced without the need to incorporate labels or coupling assays. MS-HTS also permits screening of targets that are difficult or impossible to screen by other techniques. For example, enzymes that are challenging to purify can lead to the nonspecific detection of structurally similar components of the impure enzyme or matrix of membraneous enzymes. The high selectivity of tandem mass spectrometry (MS/MS) enables these screens to proceed with low levels of background noise to sensitively discover interesting hits even with relatively weak activity. In this article, we describe three techniques that we have adapted for large-scale (approximately 175,000 sample) compound library screening, including four-way parallel multiplexed electrospray liquid chromatography tandem mass spectrometry (MUX-LC/MS/MS), four-way parallel staggered gradient liquid chromatography tandem mass spectrometry (LC/MS/MS), and eight-way staggered flow injection MS/MS following 384-well plate solid-phase extraction (SPE). These methods are capable of analyzing a 384-well plate in 37 min, with typical analysis times of less than 2 h. The quality of the MS-HTS approach is demonstrated herein with screening data from two large-scale screens.

Confirmation of moxidectin residues in cattle fat by liquid chromatography/mass spectrometry

Moxidectin, a potent new endo- and ectoparasitic agent, is determined in cattle tissues by liquid chromatography (LC) with fluorescence detection. The original confirmatory method for moxidectin in cattle fat, the target tissue for regulatory purposes, was LC with mass spectrometry (MS) using thermospray (TSP) ionization and selected ion monitoring. As newer ionization techniques for LC/MS made TSP obsolete and with the availability of a new generation of benchtop LC/MS instrumentation, the confirmation of moxidectin in cattle fat was re-evaluated. The ionization techniques of atmospheric pressure chemical ionization versus electrospray ionization, the detection techniques of single-stage MS versus tandem MS, and the instrumentation of ion trap versus quadrupole were investigated. The final confirmatory method was based on full-scan single-stage MS. Even with full-scan detection, the analysis required at least 10-fold less extract than the original TSP method. The applicability of this new confirmatory method was demonstrated on both ion trap and quadrupole instruments.

Capillary electrophoresis determinative and LC-MS confirmatory method for screening selected imidazolinone herbicides from soil

Residues of imazapyr, imazamox, imazapic, imazethapyr, imazaquin, and imazamethabenz (meta and para) are extracted from soil with 0.5 N sodium hydroxide. The pH is adjusted to 2.0-2.2, and the resulting precipitate is filtered. Compounds are trapped onto a tC18 solid-phase extraction (SPE) cartridge, then eluted from the cartridge and passed through a strong anion exchange (SAX) SPE cartridge onto a benzenesulfonic acid strong cation exchange (SCX) cartridge using ethyl acetate. After eluting the analytes from the SCX cartridge using saturated potassium chloride in methanol, the solution is evaporated and redissolved in 1% formic acid in water. The sample is then desalted using a tC18 SPE cartridge and eluted with methanol. After evaporating the methanol to dryness, the compounds are partitioned from acidic solution (pH 3.5) into methylene chloride. The methylene chloride is evaporated to dryness and the residues are then dissolved in Milli-Q water (Millipore, Bedford, MA, U.S.A.) in preparation for analysis by capillary electrophoresis. Results are calculated by direct comparison of the sample peak heights to the peak heights of bracketing standards. The validated sensitivity of the method (LOQ, limit of quantitation) is 2.0 ppb for each compound. Confirmation for individual residues greater than 2.0 ppb is provided by liquid chromatography-electrospray ionization mass spectrometry (LC-ESMS) of the final extract.

Determination of hydramethylnon residues in grass by liquid chromatography with confirmation by liquid chromatography/mass spectrometry

An improved method for determination of hydramethylnon residues in pasture grass is described. The method uses (1) the hydrochloride salt of hydramethylnon to improve its water solubility and (2) an acid-methanol precipitation to remove chlorophylls while leaving the analyte in solution. The liquid chromatographic method has a validated sensitivity of 0.05 ppm with controls showing < 0.004 ppm. The overall average recovery from 0.05 to 0.50 ppm was 98%, with a standard deviation of 11%. Samples showing a positive response (0.05 ppm or higher) and requiring mass spectrometric confirmation are directly amenable to liquid chromatography/mass spectrometry without additional sample preparation.

Liquid chromatographic determination of moxidectin residues in cattle tissues and confirmation in cattle fat by liquid chromatography/mass spectrometry

Moxidectin, a potent new endo- and ectoparasitic agent, is determined in cattle tissues by liquid chromatography (LC) with fluorescence detection. Moxidectin residues in cattle fat are confirmed with thermospray LC/mass spectrometry (MS). Moxidectin is extracted from the tissue with acetonitrile; the extract is partitioned with hexane, concentrated, and reacted with acetic anhydride, 1-methylimidazole, and dimethylformamide to produce a fluorescent product. The validated sensitivity of the LC/fluorescence method was 10 ppb, with a limit of detection typically between 1 and 2 ppb. Average recoveries from cattle fat, muscle, liver, and kidney were 99, 95, 89, and 92%, respectively. LC/MS confirmatory method determined the underivatized parent compound following the acetonitrile-hexane partitioning step, with an average recovery of 108% at the 250 ppb level in cattle fat.

Confirmation of Phorate, Terbufos, and Their Sulfoxides and Sulfones in Water by Capillary Gas Chromatography /Chemical Ionization Mass Spectrometry

A gas chromatographic/mass spectrometric method capable of confirming phorate, terbufos, their sulfoxides, and sulfones in water is reported. Parents and their metabolites are separated in less than 5 min using a short capillary GC column and high carrier gas linear velocities. Positive ion chemical ionization mass spectrometry generates (M + H) ions indicative of the different molecular weights of the analytes and at least one confirmatory fragment ion for each analyte. Residues have been qualitatively confirmed at the 1 ppb level in fortified water samples from a variety of sources. Apparent residues in control water were less than 0.1 ppb.

Confirmation of phorate, terbufos, and their sulfoxides and sulfones in water by capillary gas chromatography/chemical ionization mass spectrometry

A gas chromatographic/mass spectrometric method capable of confirming phorate, terbufos, their sulfoxides, and sulfones in water is reported. Parents and their metabolites are separated in less than 5 min using a short capillary GC column and high carrier gas linear velocities. Positive ion chemical ionization mass spectrometry generates (M + H) ions indicative of the different molecular weights of the analytes and at least one confirmatory fragment ion for each analyte. Residues have been qualitatively confirmed at the 1 ppb level in fortified water samples from a variety of sources. Apparent residues in control water were less than 0.1 ppb.

Mass spectrometric approaches to the confirmation of maduramicin alpha in chicken fat

Because of the structural information it provides, mass spectrometry has gained widespread acceptance as the preferred analytical technique for drug residue confirmatory procedures. For the confirmation of the polyether ionophore antibiotic, maduramicin alpha, in chicken fat, the techniques of desorption chemical ionization (DCI), thermospray liquid chromatography/mass spectrometry (TSP LC/MS), and thermospray liquid chromatography/tandem mass spectrometry (TSP LC/MS/MS) were investigated as potential approaches. Sample clean-up was found to be totally inadequate for DCI and only marginally acceptable for TSP LC/MS. Only TSP LC/MS/MS adequately resolved the analyte from the tissue coextractives and generated satisfactorily reproducible mass spectrometric data for a confirmatory method. The techniques developed here should be applicable to other commonly used polyether ionophores.

Confirmation of Levamisole Residues in Cattle and Swine Livers by Capillary Gas Chromatography-Electron Impact Mass Spectrometry

Capillary gas chromatography-electron impact mass spectrometry is used to confirm the presence of levamisole in cattle and swine livers at the 0.1 ppm tolerance level. Use of a fused silica capillary column from injector to detector solved chromatographic problems encountered with the analyte. Of the mass specrrometric techniques evaluated, electron impact mass spectrometry provided the most satisfactory data for a confirmatory method. Recoveries from swine and cattle livers fortified at 0.1 ppm averaged 74.9 and 72.7%, respectively, indicating potential utility of this methodology as a quantitative method. Apparent levamisole residues in control livers were less than 0.01 ppm

Confirmation of levamisole residues in cattle and swine livers by capillary gas chromatography-electron impact mass spectrometry

Capillary gas chromatography-electron impact mass spectrometry is used to confirm the presence of levamisole in cattle and swine livers at the 0.1 ppm tolerance level. Use of a fused silica capillary column from injector to detector solved chromatographic problems encountered with the analyte. Of the mass spectrometric techniques evaluated, electron impact mass spectrometry provided the most satisfactory data for a confirmatory method. Recoveries from swine and cattle livers fortified at 0.1 ppm averaged 74.9 and 72.7%, respectively, indicating potential utility of this methodology as a quantitative method. Apparent levamisole residues in control livers were less than 0.01 ppm.

Residue methodology for AMDRO fire ant insecticide (AC 217,300) in pasture grass and crops

Residue methodology is described for the determination of AC 217,300 residues in pasture grass and crop samples. After extraction and subsequent cleanup on an XAD-2 column, residues of AC 217,300 are determined by liquid chromatography (LC), using a reverse phase paired-ion chromatographic system and detection at 300 nm. The method has a validated limit of sensitivity of 0.05 ppm with corresponding control values for the commodities analyzed of less than 0.01 ppm. Apparent residues over 0.05 ppm can be confirmed by either gas chromatography with an electron capture detector (GC-EC) or gas chromatography-negative ion chemical ionization mass spectrometry (GC-NICI). The direct GC-NICI method circumvents the need for sample cleanup on the XAD-2 column, and offers a greatly simplified procedure that is useful for screening samples. Recoveries of AC 217,300 from the commodities analyzed have been satisfactory with all methods of analysis.

Residue Methodology for AMDRO Fire Ant Insecticide (AC 217,300) in Pasture Grass and Crops

Residue methodology is described for the determination of AC 217,300 residues in pasture grass and crop samples. After extraction and subsequent cleanup on an XAD-2 column, residues of AC 217,300 are determined by liquid chromatography (LC), using a reverse phase paired-ion chromatographic system and detection at 300 nm. The method has a validated limit of sensitivity of 0.05 ppm with corresponding control values for the commodities analyzed of &lt;0.01 ppm. Apparent residues over 0.05 ppm can be confirmed by either gas chromatography with an electron capture detector (GC-EC) or gas chromatographynegative ion chemical ionization mass spectrometry (GC-NICI). The direct GC-NICI method circumvents the need for sample cleanup on the XAD-2 column, and offers a greatly simplified procedure that is useful for screening samples. Recoveries of AC 217,300 from the commodities analyzed have been satisfactory with all methods of analysis

Confirmatory method for sulfamethazine residues in cattle and swine tissues, using gas chromatography--chemical ionization mass spectrometry

A gas chromatographic (GC) method has been reported for the determination of sulfamethazine residues in cattle and swine tissues. The extracts from this procedure were found to be directly amenable to examination by gas chromatography-mass spectrometry (GC-MS), allowing positive confirmation of an apparent residue of sulfamethazine. Chemical ionization mass spectrometry (CIMS) was chosen as the MS technique because it generated an ion indicative of intact sulfamethazine and fragment ions indicative of the amine functionality and sulfanil moiety. Positive ion (PI) chemical ionization mass spectrometry was adequate by itself for a confirmatory technique. Negative ion (NI) chemical ionization mass spectrometry alone could not be used for the confirmatory analysis of sulfamethazine, but it did offer a means to check the quantitative data from the positive ion analyses and provided complementary confirmatory data. Satisfactory recoveries were obtained for sulfamethazine in swine and cattle tissues at the tolerance level of 0.1 ppm. Apparent sulfamethazine residues in control tissues were less than 0.01 ppm.

Confirmatory Method for Sulfamethazine Residues in Cattle and Swine Tissues, Using Gas Chromatography-Chemical Ionization Mass Spectrometry

A gas chromatographic (GC) method has been reported for the determination of sulfamethazine residues in cattle and swine tissues. The extracts from this procedure were found to be directly amenable to examination by gas chromatography–mass spectrometry (GC-MS), allowing positive confirmation of an apparent residue of sulfamethazine. Chemical ionization mass spectrometry (CIMS) was chosen as the MS technique because it generated an ion indicative of intact sulfamethazine and fragment ions indicative of the amine functionality and sulfanil moiety. Positive ion (PI) chemical ionization mass spectrometry was adequate by itself for a confirmatory technique. Negative ion (NI) chemical ionization mass spectrometry alone could not be used for the confirmatory analysis of sulfamethazine, but it did offer a means to check the quantitative data from the positive ion analyses and provided complementary confirmatory data. Satisfactory recoveries were obtained for sulfamethazine in swine and cattle tissues at the tolerance level of 0.1 ppm. Apparent sulfamethazine residues in control tissues were less than 0.01 ppm.