Concentration gas chromatography

Most often the sterols have been collected by liquid-liquid extraction using petroleum ether and ethyl acetate [408], chloroform and methanol [409], -hexane [410,411] or chloroform [412,413]. After concentration, gas chromatography was generally used for the final separation and determination, although thin-layer chromatography has also been employed. The extra sensitivity of the electron capture detector could be used by reacting the concentrated sterols with bromomethyldimethylchlorosilane (BMDS) before separation and measurement [414],... 

J. Zechman, S. Aldinger, and J. LaBows, Jr., Characterization of pathogenic bacteria by automated headspace concentration—gas chromatography, J. Chromatogr., 377 49-57 (1986). 

The volatile constituents of canned Black Perigord Truffles (Tuber Melanosporum) were analysed by dynamic headspace concentration gas chromatography - mass spectrometry. A total of 36 compounds were identified and described for the first time as canned black truffle aroma constituents. The modification of flavor and the possible formation of the compounds due to the heating treatment are discussed. 

Zechman J.M. and Labows J.N. Jr. (1985) Volatiles of Pseudomonas aeruginosa and related species by automated headspace concentration gas chromatography. Can. J. Microbiol., 31, 232-237. 

BIOLOGICAL PROPERTIES Koc 5,181 leaching is only expected to be quick in sandy soils % degraded under anaerobic continuous flow conditions 4% in air, half of it may be broken down to other chemicals within 60 days in water, half of it may be broken down tc other chemicals within 30 days readily breaks down in soil considerable dispersion is expected did not biodegrade in an anaerobic culture incubated for 48 hrs 37°C under anaerobic conditions with domestic wastewater as the innoculum, 100% was removed after 7 days incubation 25°C soil, surface water, and aerobic half-lives 4 weeks-6 months ground water half-life 8 weeks-12 months anaerobic half-life 16 weeks-24 months can be detected in water by EPA method 612 methylene chloride extraction followed by concentration, gas chromatography plus electron capture detection, or EPA Method 625 gas chromatography plus mass spectrometry... 

The present Interest in the characterization of both animal and human secretions has paralleled the development in psychophysical measurement techniques and in analytical methods such as headspace concentration, gas chromatography, and the combination of gas chromatography/mass spectrometry (GC/MS) which have made it possible to routinely separate and identify submicrogram quantities of organic compounds. GC/MS profiling of the small organic compounds present in body secretions, such as blood serum, cerebrospinal fluid, and urine of diseased and healthy individuals, has provided useful diagnostic information (2). 

Although gas chromatography can give the concentration of each component in a petroleum gas or gasoline sample, the same cannot be said for heavier cuts and one has to be satisfied with analyses by chemical family, by carbon atom distribution, or by representing the sample as a whole by an average molecule. 

Reference methods for criteria (19) and hazardous (20) poUutants estabHshed by the US EPA include sulfur dioxide [7446-09-5] by the West-Gaeke method carbon monoxide [630-08-0] by nondispersive infrared analysis ozone [10028-15-6] and nitrogen dioxide [10102-44-0] by chemiluminescence (qv) and hydrocarbons by gas chromatography coupled with flame-ionization detection. Gas chromatography coupled with a suitable detector can also be used to measure ambient concentrations of vinyl chloride monomer [75-01-4], halogenated hydrocarbons and aromatics, and polyacrylonitrile [25014-41-9] (21-22) (see Chromatography Trace and residue analysis). 

Volatile impurities, eg, F2, HF, CIF, and CI2, in halogen fluoride compounds are most easily deterrnined by gas chromatography (109—111). The use of Ftoroplast adsorbents to determine certain volatile impurities to a detection limit of 0.01% has been described (112—114). Free halogen and haHde concentrations can be deterrnined by wet chemical analysis of hydrolyzed halogen fluoride compounds. 

Blood and urine are most often analyzed for alcohol by headspace gas chromatography (qv) using an internal standard, eg, 1-propanol. Assays are straightforward and lend themselves to automation (see Automated instrumentation). Urine samples are collected as a voided specimen, ie, subjects must void their bladders, wait about 20 minutes, and then provide the urine sample. Voided urine samples provide the most accurate deterrnination of blood alcohol concentrations. Voided urine alcohol concentrations are divided by a factor of 1.3 to determine the equivalent blood alcohol concentration. The 1.3 value is used because urine has approximately one-third more water in it than blood and, at equiUbrium, there is about one-third more alcohol in the urine as in the blood. 

Pesticides. Chlorinated hydrocarbon pesticides (qv) are often found in feed or water consumed by cows (19,20) subsequently, they may appear in the milk, where they are not permitted. Tests for pesticides are seldom carried out in the dairy plant, but are most often done in regulatory or private specialized laboratories. Examining milk for insecticide residues involves extraction of fat, because the insecticide is contained in the fat, partitioning with acetonitrile, cleanup (FlorisH [26686-77-1] column) and concentration, saponification if necessary, and determination by means of paper, thin-layer, microcoulometric gas, or electron capture gas chromatography (see Trace and residue analysis). 

Acetylene has a low solubiHty in Hquid oxygen. Excessive concentrations can lead to separation of soHd acetylene and produce accumulations that, once initiated, can decompose violently, detonating other oxidizable materials. Acetylene is monitored routinely when individual hydrocarbons are determined by gas chromatography, but one of the wet classical methods may be more convenient. These use the unique reaction of acetylene with Ilosvay s reagent (monovalent copper solution). The resulting brick-red copper acetyHde may be estimated colorimetricaHy or volumetricaHy with good sensitivity (30). 

Phenol quahty tests and analyses can be divided into two categories wet lab and Hquid and gas chromatography. In the wet lab, phenol is tested for pH, sohdification point, solubiUty in water, bromine index, color, and distillation ranges. Phenol concentration, impurities, and CHP contents are analy2ed using highly automated Hquid and gas chromatography. 

Air Monitoring. The atmosphere in work areas is monitored for worker safety. Volatile amines and related compounds can be detected at low concentrations in the air by a number of methods. Suitable methods include chemical, chromatographic, and spectroscopic techniques. For example, the NIOSH Manual of Analytical Methods has methods based on gas chromatography which are suitable for common aromatic and aHphatic amines as well as ethanolamines (67). Aromatic amines which diazotize readily can also be detected photometrically using a treated paper which changes color (68). Other methods based on infrared spectroscopy (69) and mass spectroscopy (70) have also been reported. 

Several properties of the filler are important to the compounder (279). Properties that are frequentiy reported by fumed sihca manufacturers include the acidity of the filler, nitrogen adsorption, oil absorption, and particle size distribution (280,281). The adsorption techniques provide a measure of the surface area of the filler, whereas oil absorption is an indication of the stmcture of the filler (282). Measurement of the sdanol concentration is critical, and some techniques that are commonly used in the industry to estimate this parameter are the methyl red absorption and methanol wettabihty (273,274,277) tests. Other techniques include various spectroscopies, such as diffuse reflectance infrared spectroscopy (drift), inverse gas chromatography (igc), photoacoustic ir, nmr, Raman, and surface forces apparatus (277,283—290). 

Purity of toluene samples as well as the number, concentration, and identity of other components can be readily determined using standard gas chromatography techniques (40—42). Toluene content of high purity samples can also be accurately measured by freezing point, as outlined in ASTM D1016. Toluene exhibits characteristic uv, it, nmr, and mass spectra, which are useful in many specific control and analytical problems (2,43—45). 

The identification of benzene is most easily carried out by gas chromatography (83). Gas chromatographic analysis of benzene is the method of choice for determining benzene concentrations in many diverse media such as petroleum products or reformate, water, sod, air, or blood. Benzene in air can be measured by injection of a sample obtained from a syringe directiy into a gas chromatograph (84). 

Trace impurities present in commercial benzoic acid include methyl diphenyls and phthaHc acids. The concentration and presence of these impurities vary by product grade and by manufacturer. Gas chromatography and high pressure Hquid chromatography are useful for determining the concentrations of those impurities. 

Polymerization-grade chloroprene is typically at least 99.5% pure, excluding inert solvents that may be present. It must be substantially free of peroxides, polymer [9010-98-4], and inhibitors. A low, controlled concentration of inhibitor is sometimes specified. It must also be free of impurities that are acidic or that will generate additional acidity during emulsion polymerization. Typical impurities are 1-chlorobutadiene [627-22-5] and traces of chlorobutenes (from dehydrochlorination of dichlorobutanes produced from butenes in butadiene [106-99-0]), 3,4-dichlorobutene [760-23-6], and dimers of both chloroprene and butadiene. Gas chromatography is used for analysis of volatile impurities. Dissolved polymer can be detected by turbidity after precipitation with alcohol or determined gravimetrically. Inhibitors and dimers can interfere with quantitative determination of polymer either by precipitation or evaporation if significant amounts are present. 

Concentration by gas chromatography has also been demonstrated. Elution chromatography has been used on an activated alumina column to resolve the molecular species H2, HT, and T2, thereby indicating a technique for separation or concentration of tritium (54). This method was extended (55) to include deuterium components. The technique was first demonstrated in 1964 using macro quantities of all six hydrogen molecular species (56). 

The present state technology makes it possible to detect explosives with a concentration of 10 -lO g/cnf in 30 s (with a gas chromatography) and l-t-3 s (with a drift spectrometry and its modification, mass-spectrometry). 

Fig. 15-4. Ethylene concentrations measured by the DIAL system along a 5-km path length near Menlo Park, California. The open circles are ethylene concentrations of samples taken at three ground-level locations near the line of sight and analyzed by gas chromatography. Source Murray, E. A., and Van der Laan, ). E., Appl. Opt. 17, 814-817 (1978).

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