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.     

Gas-liquid chromatographic determination of diethylstilbestrol in molasses-based liquid feed supplements.

A gas-liquid chromatographic (GLC) method is described for the determination of diethylstilbestrol (DES) in molasses-based liquid feed supplements, using dienestrol diacetate as the internal standard. A sample equivalent to 110 mug DES was diluted, acidified with dilute sulfuric acid, extracted with chloroform, and subjected to basic sodium acetate cleanup. The bis-(trimethylsilyl) acetamide derivative was prepared and determined by GLC. Interfering peaks and/or low recoveries were found to be related to emulsions and the procedure incorporates centrifugation to minimize these.     

A rapid gas-liquid chromatographic method for the multi-determination of antioxidants in fats, oils and dried food products

A rapid quantitative method for determining 8 antioxidants in various food products is described. Two procedures are employed. The first involves the use of a glass wood precolumn to separate 3(2)-tert-butyl-4-hydroxyanisole, 3,5-di-tert-butyl-4-hydroxytoluene, 4-hydroxymethyl-2,6-di-tert-butylphenol, and mono-tert-butylhydroquinone (TBHQ) from nonvolatile residues resulting from direct injection of diluted sample or sample extracts into the gas-liquid chromatographic (GLC) column. In the second procedure, the antioxidants TBHQ, 3,3'-thiodipropionic acid, n-propyl gallate, 2,4,5-trihydroxybutyrophenone, and nordihydroguaiaretic acid are isolated from food products by extraction with 70% ethanol. The antioxidant residues are then converted to trimethylsilyl derivatives, and determined by GLC, using a flame ionization detector. Recoveries of all 8 antioxidants from 28 food samples fortified at either 10 or 100 ppm ranged from 70 to 105%.     

Determination of chlorinated pesticide residues in foods. II. Potassium permanganate oxidation for cleanup of some vegetable extracts.

A potassium permanganate-dilute sulfuric acid KMnO4/dilute H2SO4 oxidation procedure was developed to supplement Florisil cleanup of some vegetable extracts. Following sample preparation and Florisil cleanup, a reaction mixture of the n-hexane eluate from the Florisil cleanup, 4% KMnO4, and 40% H2SO4 (1 + 1 + 1) was shaken in a test tube 2 min at room temperature and then centrifuged. The n-hexane phase was washed with 2 mL 0.1N NaOH and analyzed by GLC. Twelve chlorinated pesticides were completely recovered in the n-hexane phase. Aldrin was not recovered because its extreme instability caused it to decompose even in neutral solutions. Chlorinated pesticide residues in onion, garlic, carrot, and radish root were easily analyzed by the application of this oxidation procedure.     

The determination of sugars in tomato fruit: A comparison of volumetric,automated colorimetric and gas chromatographic methods

Abstract

Fifty samples of tomato fruit have been analysed for sugars using a reliable but laborious volumetric method and the results compared with those obtained both by a rapid automated colorimetric procedure employing the Technicon AutoAnalyzer and by a gas Chromatographic (GLC) technique. Using cleared fruit extracts, the overall mean results for the volumetric and automated methods were not significantly different. Automated analysis of uncleared extracts gave only slightly lower results and in view of its speed this method is recommended for the rapid routine analysis of tomato fruit. The GLC procedure gave results some 4% lower than those for cleared extracts by the other methods, but this technique has the advantage that the concentrations of the individual sugars (glucose and fructose) are readily obtained if required.     

Gas-liquid chromatography and liquid chromatography of ethylenethiourea in fresh vegetable crops, fruits, milk, and cooked foods

The Onley-Yip procedure for determining ethylenethiourea (ETU) in milk and crops was modified to reduce interferences by the ethylenebisdithiocarbamates (EBDCs). A 20 g crop-methanol extract is cleaned up by adsorbing the sample onto Gas-Chrom S. desorbing ETU, and eluting ETU from aluminum oxide with chloroform containing ethanol. ETU is converted to the S-butyl derivative for gas-liquid chromatography (GLC) and flame photometric detection (sulfur mode). For liquid chromatography (LC), ETU is cleaned up on another aluminum oxide column and injected directly. LC and GLC results are confirmed by thin layer chromatography. A cooking procedure based on conversion of EBDCs to ETU is included for surveying crops for possible EBDC content. Recoveries from 8 crops and milk fortified at 0.05 ppm ETU ranged from 73 to 100%.     

Gas-liquid chromatographic determination of individual sugars in confectionery products.

A gas-liquid chromatographic (GLC) procedure is presented for the separation and quantitative determination of sucrose, lactose, maltose, and glucose in commercial confectionery products. By converting reducing sugars to oximes and then forming trimethylsilyl ethers of these compounds and separating them on a 6 ft X 4 mm id glass column packed with 2% OV-17 on 100--120 mesh Supelcoport, single peaks were obtained for each of the sugars. Results for sugars present in samples at levels of 5% or more are within 2.8%, on the average, of results obtained by polarization measurements. The data also compare favorably with others in the literature on similar products analyzed by other GLC procedures that do not involve oxime formation.     

Gas-liquid chromatographic determination of 3,6-dichloropicolinic acid in soils.

A gas-liquid chromatographic (GLC) method has been developed for the determination of the experimental herbicide 3,6-dichloropicolinic acid (Dowco 290) in soils. The method involves extraction of 1 g soil samples with 1N NaCl at approximately pH 7, methylation with diazomethane utilizing a microgenerator, and detection by electron capture GLC. Interferences are small, so that a cleanup step is not necessary even at the 6 ppb level. The procedure is rapid, requiring only 45 min/sample. Recoveries range from 84 to 94% at the 6-1000 ppb level with a minimum detectable limit of 6 ppb. Standard deviations for the percentage recovery values vary from 10.9 to 2.3 for the tested range of 6.7-670 ppb, respectively.     

Extraction and cleanup procedures for determination of diarylphosphates in fish, sediment, and water samples

Methods for determination of triaryl/alkylphosphates (TAPs) in water, fish, and sediment have been extended to determination of the diarylphosphate (DAP) degradation products. DAPs were extracted from water (adjusted to pH 0.5) by use of XAD-2 resin and determined by gas-liquid chromatography as butyl esters. Recovery of diphenylphosphate (DPP) and o-, m-, p-dicresylphosphates (DoCP, DmCP, DpCP) were greater than 95% in water samples fortified at 1, 10, and 50 micrograms/L. DAPs were extracted from fish with methanol and the extracts were cleaned up on reverse phase (C18) silica cartridges. Recoveries were greater than 87% for DPP, DoCP, DmCP, and DpCP in fish muscle fortified at 50, 100, and 500 ng/g. Sediments were refluxed with aqueous methanol and DAPs were recovered by use of XAD-2 resin. Recoveries of DAPs from sediments fortified at 50 and 100 ng/g were greater than 76%. Interferences (1-10 ng/g) from phosphorus or nitrogen-containing GLC peaks prevented sub- ng/g level analysis for DAPs in sediment and fish extracts.     

Digestion of plants and organic soils using nitric acid,hydrogen peroxide and UV irradiation

Abstract

A two‐step digestion procedure using HNO₃ and H₂O₂/UV irradiation is described. The samples are predigested with HNO₃, succeeded by digestion in H₂O₂ under UV irradiation. The maximum temperature is 150°C. The digestion is performed without sample transfer during oxidation. The analytical data obtained by the new digestion method do not deviate from those obtained by HClO₄ digestion. The macronutrient elements including P were measured.     

RP-HPLC analysis of the phenolic compounds of plant extracts. investigation of their antioxidant capacity and antimicrobial activity

Extracts of aromatic plants of Greek origin were examined as potential sources of phenolic compounds. RP-HPLC with UV detection was employed for the identification and quantification of the phenolic antioxidants, present in methanolic extracts. The most abundant phenolic acids were ferulic acid (1.1-280 mg/100 g of dry sample) and caffeic acid (1.2-60 mg/100 g of dry sample). (+)-Catechin and quercetin were the most abundant flavonoids. Apigenin and luteolin were detected in high amounts in Menta pulegium and Thymus vulgaris, respectively. The antioxidant capacity was determined, in dried ground plants and in their methanol extracts, with the Rancimat test using sunflower oil as substrate. Both pulverized plants and extracts showed antioxidant capacity. Total phenolic content in the extracts was determined spectrometrically according to the Folin-Ciocalteu assay and ranged from 1 to 21 mg of gallic acid/100 g of dry sample. Antimicrobial activity of the extracts against selected microbes was also conducted in this study.     

Quantitation of polychlorinated biphenyl residues by electron capture gas-liquid chromatography: reference material characterization and preliminary study.

Weight per cent compositions of individual peaks of Aroclors 1016, 1242, 1248, 1254, and 1260 were determined under standard gas-liquid chromatographic (GLC) conditions. The GLC peak compositions were determined by using a Hall electrolytic conductivity detector for chlorine measurement and chemical ionization mass spectrometry with single ion monitoring for molecular weight characterization. The Aroclors used are available as reference materials for individual peak quantitation of polychlorinated biphenyl (PCB) residues by electron capture GLC. On the basis of a limited interlaboratory study and a collaborative study, the individual peak method shows improved interlaboratory precision and/or accuracy in PCB quantitation over existing methods.     

Lack of correlation between gas-liquid chromatograph and UV absorption indicators of petroleum pollution in organisms

An attempt was made to see if simple liquid-solid chromatography with a UV absorption detector could be used to monitor non-point source petroleum pollution in organisms instead of gas-liquid chromatography (GLC). Petroleum derived material in nine algal communities and in 10 invertebrate populations on the rocky shores of Bermuda was analyzed by both methods. No significant linear or logarithmic relationship was found between the results obtained by the two different methods. Therefore it was decided that UV absorption measurements could not be used for monitoring non-point source petroleum pollution. There was a very significant correlation (r=0.99) between the area of the unresolved envelope of the chromatograms and the total amount of petrogenic hydrocarbons (PHC) found by GLC. This relationship was found to be valid in the range of 2.5 μg to 315 μg PHC per g of tissue (wet weight). Therefore in a monitoring program it should be sufficient to measure the unresolved envelope alone without the need of determining the total PHC content.     

Modified method for electron capture gas-liquid chromatographic determination of diethylstilbestrol residues in urine of fattened bulls

A gas-liquid chromatographic (GLC) method with electron capture (EC) detection was developed for determining diethylstilbestrol residues in the urine of fattened bulls. Diethylstilbestrol (DES) is extracted into benzene, and then into 1N sodium hydroxide. The pH of the phenolic fraction (alkaline phase) is adjusted to 10.2 and DES is extracted again into benzene. Sample extracts are cleaned up on silica gel. Trifluoroacetic anhydride (TFAA) is used as acylation reagent, and the derivatized sample is chromatographed on a 3% OV-17 column and measured with a 63Ni EC detector. The method is suitable for determining residues at levels as low as 2 ppb.     

Characterization of protein fractions from Bt-transgenic and non-transgenic maize varieties using perfusion and monolithic RP-HPLC. Maize differentiation by multivariate analysis

Protein fractions from transgenic Bt and non-transgenic maize varieties, extracted by the Osborne solvent fraction procedure, were characterized for the first time by perfusion and monolithic RP-HPLC in very short analysis times. Albumins and globulins from different transgenic Bt maizes as well as from their non-transgenic isogenic varieties were eluted in four peaks using perfusion RP-HPLC, whereas prolamins and glutelins were separated in seven peaks. Monolithic RP-HPLC enabled the separation of maize proteins in a large number of peaks showing 6 and 10 main peaks for albumins and globulins, respectively. Prolamins migrated at retention times higher than 5 min as seven peaks, whereas glutelins were separated in three main peaks appearing at retention times higher than 6.0 min. Moreover, chromatograms of the whole protein extracts showed 8 and 11 components for perfusion and monolithic RP-HPLC, respectively. A comparison of the chromatograms of the whole protein extracts relative to transgenic and non-transgenic varieties evidenced quantitative differences on the percentages of area, mainly for peaks 2 and 3 by perfusion RP-HPLC and for peaks 3 and 7 by monolithic RP-HPLC. A discriminant analysis based on these proteic profiles was carried out to classify and predict transgenic Bt maize lines, achieving 100% correct classification using perfusion RP-HPLC.     

Gas-liquid chromatographic determination of beta-asarone in wines and flavors.

Wine samples containing beta-asarone (cis-2,4,5-trimethoxy-l-propenylbenzene) are distilled; beta-asarone is extracted by hexane and then quantitatively determined by gas-liquid chromatography (GLC), using ethyl palmitate as the internal standard. The GLC procedure is rapid and yields precise and accurate results. Mass spectrometry confirmed the identity of the GLC peak as beta-asarone. The ultraviolet spectra of beta-asarone and its isomer were also determined.     

Extraction and cleanup of organochlorine, organophosphate, organonitrogen, and hydrocarbon pesticides in produce for determination by gas-liquid chromatography.

A rapid, multiresidue procedure utilizing the minimal cleanup necessary for gas-liquid chromatographic (GLC) analysis is presented. The samples are extraced with acetone and partitioned with methylene chloride-petroleum either to remove water. The organophosphorus and organonitrogen compounds are then quantitated by GLC, using a KCl thermionic detector. A Florisil cleanup of the extract is performed prior to the determination of organochlorine compounds by a GLC electron capture detector. Carbon-hydrogen compounds such as biphenyl and o-phenylphenol undergo the Florisil cleanup and may also be quantitated by GLC. Quantitative recoveries for 15 organophosphorus, 9 organochlorine, 5 organonitrogen, and 2 hydrocarbon pesticides show the range in polarities of pesticides recovered, from Monitor to biphenyl. The method is simple and fast with a great potential for the analysis of many more compounds.     

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%.     

Analysis of pesticide residues by chemical derivatization. II. N-methylcarbamates in natural water and soils.

A method for the quantitative determination of several N-methylcarbamates in natural waters and the applicability of the derivative to soil samples using a previously published extraction procedure are described. After extraction of the carbamates from the substrate, the carbamates are hydrolyzed in a 10% methanol-potassium hydroxide solution to form the phenolic hydrolysis products, which are isolated and derivatized with pentafluorobenzyl (PFB) bromide to produce the PFB ether derivatives. The PFB derivatives are cleaned up and fractionated on a silica gel microcolumn and determined by electron capture gas-liquid chromatography (GLC). Eight organophosphate pesticides and 2 phthalate acid esters that hydrolyze to phenols or phthalic acid were evaluated as potential interferences and were found not to interfere with any of the carbamates tested. Quantitative determinations of 0.1 mug carbofuran and 3-ketocarbofuran and 0.5 mug carbaryl, metmercapturon, and Mobam in a 1 L water sample are possible. Propoxur was not determined at levels less than 1 mug/L due to the short GLC retention time of the derivative and interferences from the reagents at the lower levels.     

An evaluation of methods for measurement of pesticides in sorption experiments

Abstract

The concentration of four pesticides (2,4‐D, atrazine, phorate, and terbufos) in soil solution during sorption experiments was measured using UV spectrophotometry, Gas Liquid Chromatography (GLC), High Performance Liquid Chromatography (HPLC), and radiotracer technique. The presence of water soluble organic matter in soil solution interfered with the measurement of pesticide using the UV spectrophotometry. The use of GLC, HPLC, and radiotracer technique involving ¹⁴C gave a good estimate of the concentration of pesticide in soil solution. The pesticide remaining in soil can be quantitatively analyzed by extracting with a scintillation solution containing an organic solvent such as toluene or dioxane. Among the various centrifuge tubes glass tubes with Teflon caps sorbed negligible amount of pesticides and these tubes can be used for the sorption measurements.