Simultaneous determination of alachlor, metolachlor, atrazine, and simazine in water and soil by isotope dilution gas chromatography/mass spectrometry

A multiresidue method was developed for the simultaneous determination of low parts per billion (ppb) concentrations of the herbicides alachlor, metolachlor, atrazine, and simazine in water and soil using isotope dilution gas chromatography/mass spectrometry (GC/MS). Known amounts of 15N,13C-alachlor and 2H5-atrazine were added to each sample as internal standards. The samples were then prepared by a solid phase extraction with no further cleanup. A high resolution GC/low resolution MS system with data acquisition in selected ion monitoring mode was used to quantitate herbicides in the extract. The limit of detection was 0.05 ppb for water and 0.5 ppb for soil. Accuracy greater than 80% and precision better than 4% was demonstrated with spiked samples.     

A validated method for gas chromatographic analysis of gamma-aminobutyric acid in tall fescue herbage

Gamma-aminobutyric acid (GABA) is an inhibitory neurotransmitter in animals that is also found in plants and has been associated with plant responses to stress. A simple and relatively rapid method of GABA separation and quantification was developed from a commercially available kit for serum amino acids (Phenomenex EZ:faast) and validated for tall fescue (Festuca arundinacea). Extraction in ethanol/water (80:20, v/v) at ambient temperature yielded detectable amounts of GABA. Clean separation from other amino acids in 28 min was achieved by gas chromatography (GC) with flame ionization detection (FID), using a 30 m, 5% phenyl/95% dimethylpolysiloxane column. The identity of the putative GABA peak was confirmed by GC with mass spectrometric (MS) detection. The relatively small effects of the sample matrix on GABA measurement were verified by demonstrating slope parallelism of GABA curves prepared in the presence and absence of fescue extracts. Limits of quantification and detection were 2.00 and 1.00 nmol/100 microL, respectively. Method recoveries at two different spike levels were 96.4 and 94.2%, with coefficients of variation of 7.3 and 7.2%, respectively.     

Purge and trap method for determination of ethylene dibromide in table-ready foods

An improved method has been developed for the determination of ethylene dibromide (EDB, 1,2-dibromoethane) in a variety of table-ready foods. Samples are mixed with water and sparged with nitrogen for 1 h with stirring in a water bath at 100 degrees C. The EDB collected on the adsorbent Tenax TA is eluted with hexane and determined by gas chromatography (GC) with electron capture (EC) and confirmed with Hall electrolytic conductivity (HECD) detection using a second GC column. The highest levels of EDB were also confirmed by full scan GC/mass spectrometry (GC/MS). Twenty-five table-ready foods from the Food and Drug Administration's Total Diet Study that were analyzed by this method exhibited levels up to 70 ppb (pecans). Recoveries from fortified samples ranged from 91 to 104%. Values from this procedure were compared to those obtained by a modified Rains and Holder codistillation method. In all 25 samples this purge and trap procedure showed equivalent or superior recoveries and detected levels of EDB.     

Purge and trap method for determination of ethylene dibromide in whole grains, milled grain products, intermediate grain-based foods, and animal feeds

An improved method has been developed for the determination of ethylene dibromide (EDB; 1,2-dibromoethane) in whole grains, milled grain products, intermediate grain-based foods, and animal feeds. Samples are mixed with water and sparged with nitrogen for 1 h with stirring in a water bath at 100 degrees C. The EDB collected on the adsorbent Tenax TA is eluted with hexane and determined by gas chromatography (GC) with electron capture detection (ECD) and confirmed with Hall electrolytic conductivity detection (HECD) using a second GC column. The highest levels of EDB were also confirmed by full scan GC/mass spectrometry (GC/MS). A total of 24 whole grains, milled grain products, intermediate grain-based foods, and animal feeds analyzed by using this method contained EDB levels up to 840 ppb (wheat). Recoveries from fortified samples ranged from 90 to 105%. Values from this method were compared with those obtained from the acetone soak method; for all 24 samples, this purge and trap method gave equivalent or superior recoveries and detected levels of EDB. Chromatograms for this purge and trap method were clean, enabling a quantitation level of 0.5 ppb to be achieved.     

A gas chromatography-flame ionization detection method for detection of fusaproliferin in corn

A sensitive and accurate detection method is of great importance in monitoring fusaproliferin levels in foods and animal feeds and evaluating its potential hazard to human and animal health. Several methods have been developed to detect fusaproliferin in cereals and cereal-related products, including thin-layer chromatography, high-performance liquid chromatography, enzyme-linked immunosorbent assay, liquid chromatography-mass spectrometry (MS), gas chromatography (GC), and GC-MS. However, these detection methods either suffer from low sensitivity, need expensive instruments, or are susceptible to interfering substances in the sample matrix. The GC-flame ionization detector method developed herein is sensitive, reliable, and easy to use for detecting fusaproliferin in corn and corn-based samples. Its detection limits were 0.04 ng for standard trimethylsilyl-fusaproliferin and about 5 ppb for fusaproliferin in corn samples. The limits of quantitation of this method were 0.15 ng fusaproliferin/injection and 20 ppb of fusaproliferin in corn samples. The recovery rates of fusaproliferin from corn samples spiked with 200, 1000, and 5000 ppb standard fusaproliferin were 109, 85.7, and 98.9% on average. The repeatability of the method was acceptable when evaluated by the Horwitz equation. Of the tested corn samples, three out of five sweet corn and the three yellow corn samples were found to have low levels of fusaproliferin (9.4-45.3 ppb). A moldy corn sample had a fusaproliferin content of 297 ppb.     

Automated gas chromatographic method for the determination of ethanol in canned salmon

A method has been developed for the determination of ethanol in canned salmon using automated headspace sampling in conjunction with analysis by gas chromatography. The thermal process for the commercial sterilization of canned salmon is shown to provide an effective extraction of the ethanol so that the fluid removed from the can may be used as the analytical sample with minimal preparation prior to analysis. Ethanol content is measured directly, without the need for an internal standard, by either GC/MS or GC/FID. The headspace autoanalyzer allows for a rapid determination of ethanol with greater reproducibility than could be obtained with manual injection systems. The GC/MS technique can also provide an advantage in that simultaneous single ion monitoring of the two major ethanol ions provides additional protection from interferences. To assess the applicability of this technique to other substrates, Atlantic sea scallop meats were also successfully analyzed by this technique.     

Chemical composition of volatile extract and biological activities of volatile and less-volatile extracts of juniper berry (Juniperus drupacea L.) fruit

Volatile chemicals in a dichloromethane extract from a steam distillate of juniper berry fruit (Juniperus drupacea L.) and its two column chromatographic fractions (eluted with hexane and ethyl ether) were analyzed by gas chromatography/mass spectrometry. The major compounds in the dichloromethane extract were alpha-pinene (23.73%), thymol methyl ether (17.32%), and camphor (10.12%). A fraction eluted with hexane contained alpha-pinene (44.24%) as the major constituent. A fraction eluted with ethyl ether had thymol methyl ether (22.27%) and camphor (19.65%) as the main components. Three samples prepared from the distillate and two additional samples prepared by petroleum ether and ethanol extraction directly from juniper berry fruits exhibited clear antioxidant activities with dose response in both 1,2-diphenyl picrylhydrazyl and beta-carotene assays. All samples except the hexane fraction showed comparable activities to that of the synthetic antioxidant t-butyl hydroquinone at a level of 200 microg/mL in the two testing systems. The extracts of dichloromethane, petroleum ether, and ethanol exhibited appreciable antimicrobial activities against six microorganisms with minimum inhibitory concentrations ranging from 0.5 mg/mL (volatile extract against Candida albicans ) to 1.2 mg/mL (ethanol extract against Aspergillus niger ). The results of the present study suggest that this fruit could be a natural antioxidant supplement for foods and beverages.     

Rapid gas chromatographic method for determining ethyl carbamate in alcoholic beverages with thermal energy analyzer detection

A rapid column elution method has been developed for the determination of ethyl carbamate (EC) in alcoholic beverages. The beverage is mixed with Celite and packed in a column containing deactivated alumina capped with a layer of sodium sulfate. EC is then eluted with methylene chloride. The method, using a gas chromatograph-thermal energy analyzer with a nitrogen converter for detection and quantitation of EC, has been applied to a variety of alcoholic beverages. Recoveries +/- standard deviations of EC in wine and whisky fortified at the 20 and 133 micrograms/kg (ppb) levels averaged 87.3 +/- 5.3 and 88.7 +/- 3.6%, respectively. The method has a limit of detection of 1.5 ppb. Gas chromatography/mass spectrometry/mass spectrometry was used to confirm the identity and quantitation of EC in selected beverage extracts.     

Gas chromatographic determination of systemic fungicide tricyclazole in soil and water

A method is described for determination of tricyclazole residues in soil and water. Tricyclazole is extracted from soil by refluxing with ethyl acetate-acetone (80 + 20 v/v) and from water by partitioning into dichloromethane. The soil extract is purified by coagulation. The compound is detected and measured by gas chromatography using a flame photometer operated in the sulfur mode. Detection limits are 8 ppb for soil and 0.8 ppb for water. Recoveries for control samples fortified with tricyclazole at 0.1-5.0 ppm averaged 97.1% for soil and 108.1% for water.     

Purge and trap method for determination of volatile halocarbons and carbon disulfide in table-ready foods

A method developed for the determination of ethylene dibromide in table-ready foods has been modified and expanded to include 7 other volatile halocarbons and carbon disulfide. Samples are stirred with water and purged with nitrogen for 0.5 h in a water bath at 100 degrees C. The analytes collected on a duplex trap composed of Tenax TA and XAD-4 resin are eluted with hexane and determined by gas chromatography with electron capture detection or Hall electrolytic conductivity detection. Flame photometric detection in the sulfur mode is used to determine carbon disulfide. Thick-film, wide-bore capillary columns are used exclusively in both the determination and confirmation of the halogenated analytes. The higher levels of analytes are also confirmed by full scan gas chromatography mass spectrometry (GC/MS). Samples are analyzed for carbon disulfide, methylene chloride, chloroform, 1,2-dichloroethane, methyl chloroform, carbon tetrachloride, trichloroethylene, 1,2-dibromoethane, and tetrachloroethylene. Initially, 19 table-ready foods from the Food and Drug Administration's Total Diet Study were analyzed by this method. A limited survey of those food items exhibiting high levels of analytes was conducted. Samples exhibited levels up to 3300 ppb (methyl chloroform in Parmesan cheese). Recoveries of all 9 analytes from fortified samples ranged from 83 to 104%. Chromatograms from this purge and trap method are clean, enabling quantitation levels of low parts per billion and sub-parts per billion to be achieved for the halogenated analytes. The quantitation limit for carbon disulfide is 12 ppb. Two compounds found in drinking water were identified by GC/MS as bromodichloromethane and chlorodibromomethane. Drinking water from several cities was analyzed for these trihalomethanes as well as for bromoform. Levels of up to 17 ppb bromodichloromethane were found. Recoveries ranged from 96 to 103%.     

Capillary column gas chromatographic determination of ethyl carbamate in alcoholic beverages with confirmation by gas chromatography/mass spectrometry

A method is described for determining ethyl carbamate at low microgram/kg levels in several types of alcoholic beverages by capillary column gas chromatography with Hall electrolytic conductivity detection and confirmation by mass spectrometry. Samples are diluted to obtain a uniform concentration of ethanol (ca 10%) then saturated with NaCl and extracted with methylene chloride. Extracts are evaporated to a small volume and injected in ethyl acetate solution for chromatographic analysis. The method was evaluated by 5 laboratories, 4 employing the Hall detector and one using mass spectrometric detection. Overall between-laboratory mean percent recoveries were: wine, 85.3 +/- 21.0% coefficient of variation (CV) (spiking level 20-45 micrograms/kg); sherry, 83.8 +/- 16.1% CV (spiking level, 81-142 micrograms/kg); whiskey, 79.5 +/- 13.9% CV (spiking level 127-190 micrograms/kg); and brandy, 85.0 +/- 12.5% CV (spiking level 297-446 micrograms/kg). Mass spectrometric results agreed well with the Hall results for all commodities. Detection limits were about 5 micrograms/kg for the Hall detector and about 0.5 microgram/kg for mass spectrometric detection.     

Analysis of ethyl carbamate in wines using solid-phase extraction and multidimensional gas chromatography/mass spectrometry

The method describes a rapid and accurate procedure for the analysis of ethyl carbamate in wines. The separation of the ethyl carbamate (EC), the target analyte, from alcohol and the sample matrix is a challenge to many analytical chemists. After alcohol removal from the sample, EC was extracted and concentrated by solid-phase extraction. For analysis of EC, large-volume injection on a programmable temperature vaporization (PTV) inlet was used followed by multidimensional gas chromatography/mass spectrometry (MDGC/MS) using electron-impact ionization (EI). For quantitation, the ratio of ions produced during EI at m/z 62 (EC) and 64 (isotopically labeled EC) was monitored. The use of solid-phase extraction and MDGC/MS removes the majority of the matrix interference encountered in other methods. A linear dynamic range was established from 0.387 to 1160 ng/mL, with a limit of detection at 0.1 ng/mL and limit of quantitation at 1 ng/mL.     

Determination and confirmation of 5-hydroxyflunixin in raw bovine milk using liquid chromatography tandem mass spectrometry

A method was developed and validated to determine 5-hydroxyflunixin in raw bovine milk using liquid chromatography tandem mass spectrometry (LC/MS/MS). The mean recovery and percentage coefficient of variation (%CV) of 35 determinations for 5-hydroxyflunixin was 101% (5% CV). The theoretical limit of detection was 0.2 ppb with a validated lower limit of quantitation of 1 ppb and an upper limit of 150 ppb. Accuracy, precision, linearity, specificity, ruggedness, and storage stability were demonstrated. A LC/MS/MS confirmatory method using the extraction steps of the determinative method was developed and validated for 5-hydroxyflunixin in milk from cattle. Briefly, the determinative and confirmatory methods were based on an initial solvent (acetone/ethyl acetate) precipitation/extraction of acidified whole milk. The solvent precipitation/extraction effectively removed incurred ((14)C) residues from milk samples. The organic extract was then purified by solid phase extraction (SPE) using a strong cation exchange cartridge (sulfonic acid). The final SPE-purified sample was analyzed using LC/MS/MS. The methods are rapid, sensitive, and selective and provide for the determination and confirmation of 5-hydroxyflunixin at the 1 and 2 ppb levels, respectively.     

A gas chromatography/electron ionization-mass spectrometry-selected ion monitoring method for determining the fatty acid pattern in food after formation of fatty acid methyl esters

A method using gas chromatography/electron ionization-mass spectrometry (GC/EI-MS) in the selected ion monitoring (SIM) mode was developed for the analysis of fatty acids as methyl esters (FAMEs) in order to determine their percentage contribution to the fatty acid profile in food. In the GC/EI-MS-SIM mode, saturated fatty acids were determined with m/z 87, monoenoic fatty acids were determined with m/z 74, and polyenoic fatty acids were determined via the sum of m/z 79 and m/z 81. The ratios of these fragment ions and the GC retention data provided additional information for tentative structural assignments. The 28 FAME standards tested provided similar results for the novel GC/EI-MS-SIM method and GC/EI-MS in the full scan mode, both of which were slightly worse than GC/flame ionization detection (FID). Analysis of sunflower oil, suet, and cod liver oil verified that both major and minor fatty acids (20-60% and down to 0.001% contribution to the fatty acid pattern) were determined with sufficient quality that justifies application of the GC/EI-MS-SIM method for the analysis of food samples. Furthermore, the method was approximately 20- or approximately 10-fold more sensitive than GC/EI-MS in the full scan mode or GC/FID, respectively. The method is suited for both quantitative purposes and fatty acid identification in samples where only low amounts of lipids are available.     

Ethyl carbamate levels in selected fermented foods and beverages

Ethyl carbamate (EC), also known as urethane, is an animal carcinogen and a by-product of fermentation. Because EC has been found in distilled spirits and wines, a variety of fermented foods and beverages were analyzed to assess its occurrence in other products. Previously described methods using a gas chromatograph-thermal energy analyzer with a nitrogen converter were modified for each matrix and gave recoveries of greater than 80%, with a limit of detection in the 1-2 micrograms/kg (ppb) range. A total of 152 test samples were analyzed; EC levels ranged from none found to 3 ppb in 15 cheeses, 6 teas, 12 yogurts, and 8 ciders; from none found to 13 ppb in 30 breads and 69 malt beverages; and from none found to 84 ppb in 12 soy sauces. Gas chromatography/mass spectrometry/mass spectrometry was used to confirm EC identity and to quantitate EC in selected food extracts.     

Changes in the volatile compounds and chemical and physical properties of Kuerle fragrant pear (Pyrus serotina Reld) during storage

Volatiles from stored Kuerle fragrant pears (Pyrus serotina Reld) were studied using high-resolution gas chromatography and the solid-phase microextraction (SPME) method of gas chromatography/mass spectrometry (GC/MS). The dominant components were hexanal, ethyl hexanoate, ethyl butanoate, ethyl acetate, hexyl acetate, ethanol, alpha-farnesene, butyl acetate, and ethyl (E,Z)-2,4-decadienoate. By using GC-olfactometry, it demonstrated that the volatile compounds from SPME were responsible for the aroma of the Kuerle fragrant pear. The levels of sugars, organic acids, and phenolic acids in Kuerle fragrant pears were investigated using high-performance liquid chromatography (HPLC). Fructose was the dominant sugar, followed by glucose and sucrose. With increasing storage time, sucrose levels decreased; however, changes in fructose and glucose levels were not remarkable. There was a slight decrease in flesh firmness during storage. The general soluble solids concentration (SSC) declined slightly after 5 months storage. Some aroma-related volatile components increased during storage, while others decreased, especially the esters. The organic acids and phenolic acids also changed. The flavor of the Kuerle fragrant pears was affected by the change of volatile compounds and changes in chemical and physical properties.     

Quantitation of total folate in whole blood using LC-MS/MS

An accurate method for measuring whole blood total folate using liquid chromatography with tandem mass spectrometry is described and compared to GC/MS and a chemiluminescence assay. Whole blood from normal adults (n = 15) was fortified with a [(13)C(6)]para-aminobenzoic acid (pABA) internal standard and treated with 12.1 N hydrochloric acid at 110 degrees C for 4 h to hydrolyze all folates to pABA. Contaminants in the hydrolysate were adsorbed onto a C18 SPE cartridge. The eluate containing the folate catabolite pABA was partitioned into ethyl acetate and methylesterified with trimethylsilyldiazomethane. The methyl-pABA derivatives were quantified by positive-ion atmospheric pressure chemical ionization (APCI)LC-MS/MS. An isocratic mobile phase of acetonitrile-water (70:30) (v/v) on a C18 analytical column was used with a postcolumn reagent of 0.025% formic acid. The limit of quantitation for folate was 56.6 nmol/L RBC, and the limit of detection was 22.6 nmol/L RBC. Folate levels as determined by LC-MS/MS correlated well with the chemiluminescence assay and a GC/MS method. This new LC-MS/MS method provides enhanced sample throughput (n = 36 per day) as compared to GC/MS methods. LC-MS/MS will enable accurate measurements of red blood cell (RBC) folate in nutrition surveys and clinical trials.     

Capillary column gas chromatographic determination of dicamba in water, including mass spectrometric confirmation

A sensitive method is described for determining dicamba at low micrograms/L levels in ground waters by capillary column gas chromatography with electron-capture detection (GC-EC); compound identity is confirmed by gas chromatography-mass spectrometry (GC-MS) using selected ion monitoring. Dicamba residue is hydrolyzed in KOH to form the potassium salt. The sample is then extracted with ethyl ether which is discarded. The aqueous phase is acidified to pH less than 1 and extracted twice with ethyl ether. The combined ethyl ether extracts are concentrated, and the residue is methylated using diazomethane to form the corresponding dicamba ester. The derivatized sample is cleaned up on a deactivated silica gel column. The methylated dicamba is separated on an SE-30 capillary column and quantitated by electron-capture or mass spectrometric detection. Average recoveries (X +/- SD) for ground water samples fortified with 0.40 microgram/L of dicamba are 86 +/- 5% by GC-EC and 97 +/- 7% by GC-MS detections. The EDL (estimated detection limit) for this method is 0.1 microgram dicamba/L water (ppb).     

Improved gas chromatographic method for quantitation of deoxynivalenol in wheat, corn, and feed

A gas chromatographic (GC) method is described to determine deoxynivalenol in wheat and corn at levels as low as 20 ppb. Ground samples are extracted with water, adsorbed onto a Clin Elut column, extracted with ethyl acetate, and passed through a silica gel Sep-Pak cartridge. The final extract is then derivatized with N-heptafluorobutyrylimidazole and quantitated by GC using an electron capture detector. Recoveries are greater than 85% for spiked samples at levels of 50-1000 ppb. Results for wheat, corn, and mixed feed samples are given as well as the results of an interlaboratory study on a naturally contaminated wheat sample.     

Gas chromatographic determination of N-nitrosodialkanolamines in herbicide Di- or trialkanolamine formulations

A modified method is presented to determine trace quantities of N-nitrosodiethanolamine (NDElA) and N-nitrosodiisopropanolamine (NDiPlA) in the triisopropanolamine (TiPlA) formulation of a mixture of picloram and 2,4-D. Aqueous sample is extracted with dichloromethane to remove organic interferences, and then the aqueous layer is passed sequentially through chloride anion exchange column, hydrogen cation exchange column, and Clin-Elut extraction tube. The final eluate, 10% acetone in ethyl acetate, is concentrated. The isolated nitrosamines are converted to the corresponding trimethylsilyl (TMS) derivatives and determined by gas chromatography (GC) on a DB1 column coupled with a thermal energy analyzer (GC-TEA). Eight samples of commercial TiPlA formulations are analyzed. Maximum detected levels of NDElA and NDiPlA were 0.6 and 0.9 ppm, respectively, expressed relative to total weight of active ingredients. Analysis of 13 samples of herbicide DElA formulation using a previously established method and a DB225 column gave NDElA results of 0.7-6.0 ppm. NDiPlA was not detected in those samples. Results are confirmed by GC-mass spectrometry (GC/MS) with oxygen negative chemical ionization (ONCI) detection. Detection limits for both nitrosamines are 0.05 or 0.07 ng (0.1 or 0.17 ppm) for GC-TEA detection, depending on the analytical columns used, and 20 pg (0.04 ppm) for GC/MS detection. Recoveries of NDElA are 87-109% for DElA formulation spiked at 2.6 and 3.9 ppm and 90-115% for TiPlA formulation spiked at 0.2-0.3 ppm. Similarly, recoveries of NDiPlA are 95.7-100% for the DElA formulation spiked at 0.24 and 0.48 ppm, and 82-118% for the TiPlA formulation spiked at 0.2-0.3 ppm.