Gas Chrom Research Articles

Comparison of Dynamic Headspace Concentration on Tenax with Solid Phase Microextraction for the Analysis of Aroma Volatiles

Two different headspace extraction methods for aroma volatiles were compared: headspace solid phase microextraction (SPME), using both poly(dimethylsiloxane) (PDMS) and polyacrylate (PAc) fibers, and dynamic headspace trapping using a glass-lined stainless steel trap, containing Tenax TA. The samples studied were a cola and a diet cola. Extraction time and temperature were the same for each analysis. The dynamic headspace method extracted more volatiles from both samples than did SPME with either filament. The profile obtained using the PDMS fiber was similar to that of the Tenax TA extract but was much less intense. The PAc extract contained fewer components than the PDMS extract but included two polar volatiles not present in the other two extracts. Reproducibilities were similar for both techniques. Qualitative differences between the two cola samples were small, although the total quantity of volatiles extracted from the cola was up to 4 times greater than for the diet cola. Keywords: Cola; gas chrom...

Gas chromatographic determination of volatile alkenes by on-column bromination and electron-capture detection

A method is described for the GC-electron-capture detection determination of ultra trace quantities of alkenes via on-column bromination reactions. Copper bromide coated onto a non-polar solid support, Gas Chrom Q (100–120 mesh) acted as the bromine source. At a temperature of 90–110°C, steel wool may be used to remove selectively up to 90% of the bromine bleed from the reactor. The conversion efficiency of an alkene to the dibrominated derivative is extremely high, up to 90% for ethene, propene, butene and pentene. The bromination of acetylene is also possible, but is not as efficient.

Specific Interactions and Contact Angle Measurements on Polymer Solids

Abstract The present work examined the susceptibility of contact angle data to specific interactions taking place between solids and contacting liquids. The polymers involved were polystyrene, polyvinyl chloride and polyethylene, representing respectively basic, acidic and neutral substrates. Contacting fluids also were chosen to represent acid and base interaction categories. Significant time-dependent changes in contact angles were observed when acid/base pairs were involved in the experimental sequence. In specific cases it was possible to identify initial (zero contact time) contact angles, as well as equilibrium values, attained after prolongued contact times. Local solvation, or plasticization, of the polymer by the wetting fluid was postulated as the operative mechanism. The differences between initial and final values of the contact angles were correlated with parameters of specific interaction, calculated from the acceptor/donor numbers for the pertinent materials as measured by inverse gas chrom...

Column packings with immobilized methyl polysiloxane phases for gas chromatography

The free radical cross-linking procedure of stationary phase immobilization introduced by Grob et al. for capillary columns has been adapted for the preparation of column packings on diatomaceous supports. Immobilization of SE-30 and OV-1 on typical gas chromatography supports: Polsorb B-AW, Chromosorb W-AW, Chromosorb G-AW and Gas Chrom Q was investigated. Before immobilization, the supports (excluding Gas Chrom Q) were purified by extraction with 6 M HCl in a Soxhlet extractor and silanized with hexamethyldisilazane vapour at 300°C. The influence of the type and concentration of peroxide on the efficiency of immobilization of the silicone was studied. In order to obtain over 95% immobilization a minimum of 2% w/w of the peroxide in the stationary liquid is required. Properties of packings with immobilized phase were compared with those of related conventional packings. Adsorption activity, column efficiency and thermal stability were used for this comparison.

INFLUENCE OF DRYING AIR VOLUMES ON FATTY ACID COMPOSITION OF PECANS

`Stuart' pecans were harvested as soon as shucks would split in the fall of 1989 and 45 kg inshell samples were placed in 30 × 30 × 105 cm drying bins. The nuts were dried at air volumes of either 0, 1.27, 1.56, 1.84, or 2.12 m3/min down to 4% moisture. Air temperature in the drying bins was maintained at uniform 35°C with the exception of the 0 air volume treatment which was allowed to dry at room temperature. Four random samples of each treatment were held in frozen storage awaiting fatty acid analysis. Palmitic, stearic, oleic, linoleic, and linolinic fatty acids were separated in a 183 cm × 3 mm packed column using a 10% Silar 10C phase on a Gas Chrom QII, 100/120. The samples dried with a air volume of 1.27 m3/min retained a significantly higher oleic acid content than the 0 and 2.12 m3/min drying volumes. The 1.27 m3/min volume retained 64.55 % oleic acid compared with 61.37'% for the 0 velocity sample and 59.61% for 2.12 m3/min treatment. The more desirable oleic/linoleic ratio of 2.24 was found in the 1.27 m3/min sample compared to a 1.78 ratio in the 2.12 m3/min sample. Increased volume of air in the drying bins was thus deleterious to these samples because of the loss of monounsaturated fatty acid.

Determination of Chlordane in Laboratory-Generated Environmental Fate Samples

Abstract Trans- and cis-chlordane have been analyzed in several samples used for aquatic environmental fate studies. These samples include air, water, fish and sediments, The procedures involve extraction with various solvents followed by sulfuric acid clean-up of the extracts. The various solvents used were hexane (air and water), isopropanol/hexane (sediment), and pentane (fish). The fish were further cleaned-up using acetonitrile/pentane partitioning. Extracts were concentrated prior to analysis by GC/ECD. The GC columns used were either 12.5 or 25 m fused silica capillary column coated with OV-17 or a 2 m × 2 mm glass column packed with 3% SE-30 on 80/100 mesh Gas Chrom Q. GC/MS confirmation was conducted on selected samples. Mean recoveries of trans- and cis-chlordane from the various media ranged from 83.0 to 104.5%, with precisions ranging from 3.0 to 15.6%. The lowest recoveries and precision were found for the fish samples. Limits of detection were 0.01, 0.38 and 0.30 ppb for both trans- and cis-...

Gas-Liquid Chromatography-Mass Spectroscopy Determination of Clopamide in Plasma

A gas-liquid chromatography-mass spectroscopy(GLC-MS) method for the determination of clopamide (1) in human plasma was developed to evaluate the pharmacokinetics and bioavailability of 1 in humans. The method is specific, sensitive, and rapid and allows routine analysis as required for extensive pharmacokinetic studies. The assay procedure involves addition of furosemide (2) as an internal standard to plasma, separation on Sep Pack-C18 cartridges, elution by ether: methanol (1:1), evaporation, and subsequent derivatization with trime-thylanilinlum hydroxide in methanol (Methelute). Then, 5 μL of the reaction mixture is injected into a GLC-MS system which consists of a 1% SE-30 on Gas Chrom Q (100–120 mesh) glass column. The MS information was obtained under the following conditions: ionization beam energy 70 eV, ion source 200°; and m/e 372 for single ion monitoring. The retention times for 1 and 2 were 0.6 and 1.0 min, respectively. The limit of detection is 10 ng/mL of 1 in plasma and the calibration curve was shown to be linear between 10 and 500 ng/mL of 1. After repeated analysis of spiked plasma samples, the coefficient of variation ranged from 5.1 to 8.3%. The recovery from the extraction procedure was 92 ± 2.2%. Spiked samples frozen at —20°C were stable for at least 8 weeks. The method has been successfully used in a pharmacokinetic study with po dosing of 5mg of 1 to eight healthy volunteers. Peak plasma concentrations of 197 ± 56 ng/mL were observed after 1.1 ± 0.34h. No measurable concentration of 1 beyond 12h after dosing was observed.

The Contents of the Dufour Gland of the Ant Harpagoxenus sublaevis Nyl. (Hymenoptera: Formicidae)

Abstract The volatile components of the Dufour gland secretion of workers cf the ant Harpagoxenus sublaevis have been analysed by gas chrom atography and mass spectrometry. Over 20 com ponents have been identified, consisting of linear and terpenoid hydrocarbons. Each gland contains approximately 6 ng of hydrocarbons with n-heptadecene (40% ) and /n-heptadecadiene (30% ) as the major components. Two terpenoid hydrocarbons, (E)-β-farnesene and a homofarnesene isomer were also identified.

Use of Nitrobenzene Oxidation for Study of Lignin Composition with an Improved Method for Product Extraction ,

Sample stability, extraction procedures and solvents and various gas chromatographic procedures were studied in an attempt to improve procedures for the determination of lignin by the nitrobenzene oxidation technique. Extraction of oxidation products with ether, although needed to extract p-coumaric acid, resulted in a marked decrease in sample stability and increased extraneous material. Studies using a variety of phases and sample preparations showed that with 5% OV-25 on Gas Chrom Q the peaks corresponding to caffeic and ferulic acids were largely or entirely azoxybenzene and p-phenylazophenol. The introduction of disposable diatomaceous earth columns for extracting oxidation products resulted in a faster procedure and the removal of the by-products azoxybenzene and p-phenylazophenol from the extracted products.

Residues of Insecticides on American Elm, Cuyahoga, Co., Ohio, 1983

Abstract The crowns of street–lawn American elms, Ulmus americana L., (avg 64.0 cm in dbh; 20.1 m in height) were sampled at 16 weeks postspray to determine chemical residue. These trees were previously sprayed at bud break with candidate insecticides for evaluation against twig-crotch feeding by the smaller European elm bark beetle. Treatments were 4 insecticides applied at 2 concentrations and methoxychlor applied at 1 concentration. Each treatment was applied to 3 single tree replicates. Sevin 4-Oil was mixed in diesel fuel; all others were mixed in water. A John Bean 300G Rotomist mist blower equipped with 3 DC-5 nozzles with no. 45 cores was used. Each tree received an average of 24.6 liters of finished spray except methoxychlor-treated trees averaged 9.5 liters. When trees were sprayed on 5 May, the ambient temperature was 2–10°C, the sky was clear, and the wind was 0-5 kph. Between treatment and assay, the mean temperature was 20.6°C and the total rainfall was 37.9 cm. For assay, 5 twigs were collected from each of the 12 sectors (3 vertical levels and 4 quadrants) in each tree crown. A circular bark sample (4.5 mm2) was cut from the crotch of each twig. Samples from each vertical level were combined for assay and were analyzed on a Varian Aerograph chromatograph equipped with a 63 Ni electron capture detector. For Sevin assay, phenol conversion by the microscale derivatization technique was used. Aliquots were injected on a 0.64 cm (O.D.) by 0.6 m column packed with 2% OV-225 on 60/80 Gas Chrom Q (AW; DMCS treated). Nitrogen exit flow was 40 to 60 ml/min. Pydrin was extracted by soaking samples in hexane overnight. Aliquots were injected on a 2 mm (I.D.) by 1.2 m column packed with 3% Dexsel-300 on 100/120 Gas Chrom Q. Nitrogen exit flow was 20 to 25 ml/min. Methoxychlor extracts were prepared by soaking samples in hexane overnight. The column, 0.64 cm (O.D.) by 1.8 m, was packed with 5% DC-11 on 70/80 Aeropack 30. Nitrogen exit flow was 30 to 35 ml/min.

Recovery of grams of americium from scraps and analytical residues by means of an extraction chromatographic process using dihexy; N,N-diethyl-carbamylmethylene phosphonate (DHDECMP)

recovery of grams of americium from scraps and analytical residues by means of an extraction chromatographic process using dihexy; N,N-diethyl-carbamylmethylene phosphonate (DHDECMP)

Gas Chromatographic Determination of Nordihydroguaiaretic Acid in Larrea Divaricata

Abstract A glc analysis method utilizing a flame ionization detector was developed to determine nordihydroguaiaretic acid (NDGA). Lyophilized samples of an aqueous extract from leaves of L. divaricata were reconstituted in water at a concentration of 50 mg/ml. A 100 mcl aliquot of this solution had 50 mcl of the internal standard solution, p,p'-biphenol (0.4 mg/ml in methanol) added followed by extraction with benzene:isopropyl alcohol (98:2), evaporation, and trimethylsilylation with N,O-bis-(trimethylsilyl)-acetamide. Glc analysis was accomplished using a 10% OV-101 on 80/100 Gas Chrom Q column. Accuracy and precision for the glc method was demonstrated over the range of anticipated concentration of NDGA in the L. divaricata leaves. The content of NDGA present in the leaves was found to be 1.6%.

Variation in cephalic volatile substances in relation to worker age and behavior in the stingless bee, scaptotrigona postica

Head extracts of adult workers of the Brazilian stingless bee Scaptotrigona postica (Trigonini, Meliponinae: Apidae) were analysed for volatile substances by gas chrom atography/ mass spectroscopy. Individual worker bees performing clearly defined tasks and representing five age groups were collected. A total of 36 compounds was identified, 22 of which had not been previously described for a Trigona species. The major components are 2-heptanol, 2-tridecanone, 2-pentadecanone, Z-5-tetradecenylbutanoate and Z-7-hexadecenylbutanoate. 11 of the 36 compounds increase in concentration with age, but only 2 decrease. The other substances are present in more or less constant concentrations. These data are discussed assuming more complicated pheromone-m ediated interactions within an age-dependent polyethism between old workers acting inside and outside the nest than between young house bees

Recherche et Dosage de l'Aminocarb dans les Eaux Naturelles et le Feuillage du Sapin Baumier par Chromatographie en Phase Gazeuse

Aminocarb (4-dimethylamino-m-tolyl methylcarbamate), a carbamate insecticide, is now widely used for the control of spruce budworm (Choristoneura fumiferana) in Quebec forest spray programs. This paper describes a method for the determination of residues of this insecticide in natural waters and balsam fir foliage. The insecticide was extracted from water with chloroform and from foliage with ethyl acetate. The extracts were purified by coagulation with an aqueous solution of ammonium chloride and phosphoric acid. The acidified aqueous solution containing the insecticide was partitioned with methylene chloride, neutralized with sodium carbonate and then extracted with chloroform. The organic extract was concentrated to an appropriate volume and injected directly into a gas Chromatograph (GLC) equipped with dual nitrogen phosphorous detector (NPD). Oven and injector temperatures were reduced, and maintained respectively at 130‡C and 150‡C. Glass Columns, 60 cm × 2 mm (I.D.), in GLC were packed with a mixture of 4% OV-101 + 6% OV-210 on Gas Chrom Q (80–100 mesh), and 3% OV-17 on the same support for confirmatory analysis. Under the conditions used, aminocarb were successfully chromatographed on both columns without decomposition. Average aminocarb recoveries of more than 90% from foliage and nearly 100% from water were obtained at fortification levels of 1 Μg/g and 1 Μg/l respectively. Clean up efficiency made possible a detection limit ranging from 0.002 to 0.005 Μg/g for foliage. The detection limit for water was 0.01 Μg/l.

Analysis of the amino acid 3-methylhistidine by gas-liquid chromatography

A method for the quantitative separation of 3-methylhistidine from other amino acids, by gas-liquid chromatography, has been developed. This method gives complete resolution of the N-heptafluorobutyryl isobutyl esters of 20 amino acids with the use of a single column packed with 3% SE-30 on 100 120 mesh Gas Chrom Q. Using this method the 3-methylhistidine content of urine and meat has been determined.

Drug interactions with acetaminophen: Effects of phenobarbital, prednisone and 5-fluorouracil in normal and tumor-bearing rats

Acetaminophen (APAP) was determined by a simplified gas Chromatographic method, without derivatization, on a column packed with 3% OV17 on Gas Chrom Q. APAP, released enzymatically from its conjugates, was also so determined. Changes in urinary excretion patterns of APAP, its glucuronide (APAPGA) and its sulfate (APAPS) were studied as indicators of interference with metabolism of APAP. Effects of the presence of some tumors on APAP metabolism of hosts were examined, as were the effects of the following agents: phenobarbital, as a prototype of a hepatic enzyme inducer, prednisone and prednisolone, as alternate substrate inhibitors, and 5-fluorouracil (5-FU) and galactosamine, as possible modifiers of cofactors. Normal rats, Reuber H-35 hepatoma hosts and colon carcinoma hosts excreted 87.8 ± 8 percent of a 300 mg/kg dose of APAP, in the form of APAP plus APAPGA and APAPS. The presence of colon carcinoma did not alter significantly the quantities of APAP metabolites appearing in the urine of the hosts. Hepatoma hosts excreted significantly higher amounts of APAPGA, and early urine samples also contained elevated APAPS. These effects of the tumors were related to the presence of APAP conjugating enzymes in the hepatoma, and their virtual absence in the colon carcinoma tissue. The above effects on conjugations contrast with known depressive effects of tumors on mixed function oxidation pathways of hosts. Phenobarbital pretreatment (80 mg/kg, i.p., daily for 7–9 days) of Sprague-Dawley, or ACI, rats increased (3- to 4-fold) the amount of urinary APAPGA excreted in the first 3 hr after injection of APAP, and decreased (2-fold) the amount of unchanged APAP excreted. Coadministration of prednisone, or prednisolone (14 mg/kg, i.p.), with APAP caused a small but significant decrease in urinary APAPGA, which is consistent with the previously reported inhibitory effects of these steroids on APAP glucuronidation in vitro. Treatment of rats with 5-FU (120 mg/kg, i.p.) 3 hr prior to administration of APAP produced slight decreases in urinary APAPGA and APAPS. Contrary to expectations, pretreatment with galactosamine, on a schedule known to markedly reduce UDP-sugar pools, did not decrease urinary APAPGA. The results suggest that drugs which can induce hepatic glucuronyltransferase, or which can compete with APAP for the enzyme, rather than those that can alter UDP-sugar pools, are likely to have marked effects on APAP metabolism.

Combined Residues of Dasanit and its Three Metabolites Applied to Turnips for Control of Root Maggot in 1977 and 1978

Abstract Dasanit 15% G and 6SC were each applied to purple top white globe turnips at rates of 1, 2, and 4 oz ai/1000 ft-row at the Yakima, WA research location and at rates of 2 and 4 oz ai/1000 ft-row at Puyallup, WA experiment station in the crop years of '77 and '78. The granules were incorporated into the soil over the row in 6-in band widths at planting time; the SC was applied 30 days later as a spray directed at the base of the plants. There were 4 replications of each treatment. The laboratory procedure used for sampling, extraction, and cleanup of the extract is available on request. The combined residues were determined on harvest samples taken approximately 40 days after the spray application. The residues were determined with a Hewlett Packard 5840A gas chromatograph equipped with a nitrogen-phorphorus detector. Column: 2% OV-101 on Gas Chrom Q (100/200 mesh), glass 4 ft × 1/8 in. Known amounts of fensulfofhion and its 3 metabolites (sulfone, oxygen analog, oxygen analog sulfone) were added in the range of 0.01 to 5.00 ppm to untreated control samples prior to extraction and the percent recovery was determined.

Multiresidue Determination of Phosphoric Acid Triesters in Fish, Sea Sediment and Sea Water

An analytical method was developed for determining residue of phosphoric acid triesters (tri-n-butyl phosphate, tris (2-chloroethyl) phosphate, tri-n-amyl phosphate, tris (2, 3-dichloropropyl) phosphate, triphenyl phosphate, tris (2-butoxyethyl) phosphate, tricresyl phosphate, tris (2, 3-dibromopropyl) phosphate, tris (4-tert-butylphenyl) phosphate in fish, sea sediment and sea water. Phosphoric acid triesters were extracted from these materials with acetonitrile and methylene chloride. After n-hexane-acetonitrile partition, the extract was cleaned up by activated charcoal column chromatography, followed by extraction with conc. sulfuric acid, washing with 0.5N sodium hydroxide solution, and finally Florisil minicolumn chromatography. The purified extracts were analyzed with a gas chromatograph equipped with a flame photometric detector (P-filter) and with a gas chromatograph-mass spectrometer. The separation on gas chromatography was found to be good with 10% OV-1 on Chromosorb W experiments (AW-DMCS) and 5% FFAP on Gas Chrom Q. Throughout the present method, the recoveries of phosphoric acid triesters were in the range of 60-95%, and the detection limits (fish) were approximately 1-5μg/kg.

Differentiation between species of the Anopheles gambiae Giles complex (Diptera: Culicidae) by analysis of cuticular hydrocarbons.

Lipids were extracted from 500 female Anopheles gambiae and An. arabiensis in n-hexane and the extracts examined by gas chromatographic analysis using a glass column packed with 3% OV-1 on a 100-200 mesh Gas Chrom Q which was maintained at 225 degrees C. Cuticular hydrocarbons consisted mostly of unbranched paraffins. There were differences between the distribution of compounds with 25-29 carbons. After adjusting the C27 peak to 100%, hydrocarbons C26 and C29 represent heights of 80 and 69% in An. gambiae compared with values of 49 and 95 % in An. arabiensis. Other small but consistent differences were also found. Investigations are being performed on extracts from smaller samples and on other species within the An. gambiae complex.

GC single-run separation of C1−C10 hydrocarbons formed in gas phase radiolysis of n-pentane

Two columns in parallel are used for the separation of C1−C10 hydrocarbons: a SCOT column coated with Apiezon L and a packed column containing 2 m Durapak (phenylisocyanate/Porasil C) and 3 m 25% squalane on Gas Chrom P. The separation efficiency of the combined packed column is demonstrated by the analysis of radiolytic products of n-pentane. Special attention was given to the separation of pentenes and to their separation from the solvent peak (n-pentane). The effect of temperature on the individual separations as well as the optimal experimental conditions for the C1−C10 hydrocarbon separation are discussed. Relative retention times of the C1−C6 saturated as well as the unsaturated hydrocarbons on the combined packed column are presented.