Gas chromatography, method and

All analytical methods involve some kind of sample preparation and thus the type of factors selected for a HPLC method as shown in Table 5.2 are similar for all methods. However, different stages in the preparation will be more critical for some methods. For instance, derivatisation will be more common for gas chromatography methods and hence more critical. 

Glycerin is used in Nasonex primarily as a humectant. For its quantification, both capillary gas chromatography method and HPLC methods may be selected. The GC is equipped with a flame-ionization defector, a 0.53 mm x 30 m fused silica analytical column coated with 3.0-p,mG43 stationary phase, and a 0.53 mm x 5 m silica guard column deactivated with phenylmethyl siloxane. The carrier gas was helium with a linear velocity of about 35 cm/s. The injection port and detector temperature was maintained at 240 and 260°C, respectively. The injection mode is splitless. The column temperature is programmed to be maintained at about 40°C for 20 min, then to increase to 250°C at a rate of 10°C/min and to hold at 250°C for 15 min. 

Air samples are usually collected to solid adsorbents such as Tenax, XAD resins, graphitized carbons (e.g. Carbopak), active charcoal, or porous polymers (e.g. Chromosorb). The chemicals are eluted from the adsorbent to a liquid or gas phase by liquid-solid elution or extraction or by thermal desorption. Extraction is the most common method. Thermal desorption can be applied when analysis is by GC (gas chromatography) method, and, recently, the use of automated thermal desorption has been proposed to provide increased sensitivity in GC/MS analysis of a wide range of CWC-related chemicals 8. ... 

By the mid-1960s the majority of the gas chromatography methods and equipment still in use had been described in principle. Also the limitations of the technique had become clear. Returning to the theme of economic necessity driving analytical science, there was a need, particularly in the increasingly important pharmaceutical and agrochemical industries, for chromatographic techniques by which involatile and thermally unstable compounds could be analysed without the need for chemical derivatisa-tion. 

The use of essential oils is increasing because of the increase in the number of their apphcations and in the framework of natural and environmentally friendly materials. Many times the analysis of their components is quite complex due to the high number and the diversity of compounds in their composition. In this entry a general overview of the extraction methods is given by comparing conventional hquid-liquid and sohd-hquid methods with new alternative ones, such as supercritical fluid extraction and microwave-assisted extraction. Gas chromatography methods and examples are treated and important issues such as detection systems, modem hbraries for compounds identification, as well as multidimensional or hyphenated techniques are discussed. The use of these modem techniques and methods has improved resolution and sensitivity in essential oils determination and could open the possibihty of future work in this area of chromatography. 

Several techniques can be used to measure the hydrogen crossover rate, including the volumetric method, time-lag technique, gas chromatography method, and the electrochemical monitoring technique. For example, by applying higher pressure at one side of the membrane, Sakai et al. [13] measured the H2 permeability coefficient in Nalion membranes by using the volumetric method. 

Analytical investigations may be undertaken to identify the presence of an ABS polymer, characterize the polymer, or identify nonpolymeric ingredients. Fourier transform infrared (ftir) spectroscopy is the method of choice to identify the presence of an ABS polymer and determine the acrylonitrile—butadiene—styrene ratio of the composite polymer (89,90). Confirmation of the presence of mbber domains is achieved by electron microscopy. Comparison with available physical property data serves to increase confidence in the identification or indicate the presence of unexpected stmctural features. Identification of ABS via pyrolysis gas chromatography (91) and dsc ((92) has also been reported. 

Analytical methods iaclude thin-layer chromatography (69), gas chromatography (70), and specific methods for determining amine oxides ia detergeats (71) and foods (72). Nuclear magnetic resonance (73—75) and mass spectrometry (76) have also been used. A frequentiy used procedure for iadustrial amine oxides (77) iavolves titratioa with hydrochloric acid before and after conversion of the amine to the quaternary ammonium salt by reaction with methyl iodide. A simple, rapid quaHty control procedure has been developed for the deterrniaation of amine oxide and unreacted tertiary amine (78). 

Gas Chromatography. Aniline and many of its derivatives are volatile and can be analyzed by gas—Hquid chromatography. The method offers a rapid and accurate procedure for deterruination of aniline in mixtures and is the method of choice for quality control used by producers of aniline. 

The adsorption of gas onto a solid surface can also be used to estimate surface energy. Both inverse gas chromatography (IGC) and isotherm measurement using the BET method [19] have been used. Further discussion and detailed references are given by Lucic et al. [20] who compare the application of IGC, BET and contact angle methods for characterising the surface energies of stearate-coated calcium carbonate fillers. 

Figure 12.22 SFC-GC analysis of aromatic fraction of a gasoline fuel, (a) SFC trace (b) GC ttace of the aromatic cut. SFC conditions four columns (4.6 mm i.d.) in series (silica, silver-loaded silica, cation-exchange silica, amino-silica) 50 °C 2850 psi CO2 mobile phase at 2.5 niL/min FID detection. GC conditions methyl silicone column (50 m X 0.2 mm i.d.) injector split ratio, 80 1 injector temperature, 250 °C earner gas helium temperature programmed, — 50 °C (8 min) to 320 °C at a rate of 5 °C/min FID detection. Reprinted from Journal of Liquid Chromatography, 5, P. A. Peaden and M. L. Lee, Supercritical fluid chromatography methods and principles , pp. 179-221, 1987, by courtesy of Marcel Dekker Inc.

Using a simple solvent extraction procedure to minimize matrix effects, a diclofop-methyl immunoassay was developed for milk, a number of edible plant products, and other matrices. Gas chromatography (GC) and liquid scintillation counting (LSC) of a C-labeled analyte were used as reference methods to compare with enzyme immunoassay (EIA) results. The methods were well correlated, with comparison of EIA... 

Gortseva LV, Tarasova NA, Shutova TV, et al. 1987. [Determination of acrylonitrile in polymer materials and aqueous and oily extracts of them by the gas-chromatography method.] Gig Sanit 61-62. (Russian)... 

Verevkin, S.P., Wandschneider, D., Heintz, A. (2000) Determination of vaporization enthalpies of selected linear and branched C7, C8, C9, Cu and Cu monoolefin hydrocarbons from transpiration and correlation gas-chromatography methods. J. Chem. Eng. Data 45, 618-625. 

Mass spectrometry has become a very important technique in the identification and quantification ofphenolics in fruit and vegetables. Different factors, such as sensitivity and specificity, have been cited to explain the acceptance of this method by the scientific community. Additionally, this technique might easily combine with different separation techniques such as CE, gas chromatography (GC), and liquid chromatography (LC), including HPLC and UPLC (ultra performance liquid chromatography). 

The simplest analytical method is direct measurement of arsenic in volatile methylated arsenicals by atomic absorption [ 11 ]. A slightly more complicated system, but one that permits differentiation of the various forms of arsenic, uses reduction of the arsenic compounds to their respective arsines by treatment with sodium borohydride. The arsines are collected in a cold trap (liquid nitrogen), then vaporised separately by slow warming, and the arsenic is measured by monitoring the intensity of an arsenic spectral line, as produced by a direct current electrical discharge [1,12,13]. Essentially the same method was proposed by Talmi and Bostick [10] except that they collected the arsines in cold toluene (-5 °C), separated them on a gas chromatography column, and used a mass spectrometer as the detector. Their method had a sensitivity of 0.25 xg/l for water samples. 

A variety of methods have been used to determine pseudoephedrine hydrochloride levels in plasma and urine by gas chromatography. Bye and co-workers3s extracted basefied plasma or urine with diethyl ether. The ether extract concentrate was chromatographed on a 1.2 m x 2mm i.d. glass column packed with 2% Carbowax 20 M +5% KOH. The column was maintained at 187°C for plasma samples and 150°C for urine samples. 

Initially, progress in this area was hampered by the lack of suitable analytical methods for chiral hydrocarbons. Early studies relied on optical rotation to determine enantiomeric excess (ee) values, but with the development of chiral gas chromatography (GC) and high-performance liquid chromatography (HPLC) columns, chromatographic methods have become more common. 

Because FMs are semivolatile, they are amenable to analysis by gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS) without derivitization. Table 2 shows that all of the analytical methods developed to measure FMs in wastewater treatment to date utilize GC or GC-MS. 

Using the gas chromatography methods Sackmayereva et al. [30] obtained from spiked samples the four BHC isomers at 93-103.5% recovery. Both DDT and DDE were yielded in 85.6-94%, 90-93.2%, 90-102.4% and 92-105.8% from sediment. Purification on a Florisil column was used in determining chlorinated insecticides unstable at low pH (Aldrin, Dieldrin). The type and activity of Florisil influence the yield and accuracy of the method. Therefore, the activity of this adsorbent had to be verified and adjusted [36, 37],... 

The flash evaporation pyrolysis gas chromatography method [16] as described in section 11.1.4 for the determination of polycyclic aromatic hydrocarbons, haloorganics, aliphatic hydrocarbons, heteroaromatics, elemental sulphur and pyrolysis products of synthetic polymers in soils has also been applied to non-saline sediments. 

Chromatographic methods are classified according to the nature of the mobile and stationary phases used. The terms gas chromatography (GC) and liquid... 

Ylinen et al. [53] developed an ion-pair extraction procedure employing tetrabutylamonium (TBA) counter ions for determination of PFOA in plasma and urine in combination with gas chromatography (GC) and flame ionisation detection (FID). Later on, Hansen et al. [35] improved the sensitivity of the ion-pair extraction approach using methyl tertiary butyl ether (MTBE) and by the inclusion of a filtration step to remove solids from the extract making it amenable to liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) determination. Ion-pair extraction procedure has been the basis of several procedures for biota [49,54-58] and food samples [50,59,60]. However, this method has shown to have some limitations, such as (1) co-extraction of lipids and other matrix constituents and the absence of a clean-up step to overcome the effects of matrix compounds and (2) the wide variety of recoveries observed, typically ranging. 

ASTM. 1988. Standard practice for measuring volatile organic matter in water by aqueous-injection gas chromatography - method D 2908-87. In 1988 annual book of ASTM standards. Vol. 11.02. Water II. Philadelphia, PA American Society for Testing and Materials, 46-51. 

EPA. 1989d. Measurement of volatile aromatic and unsaturated organic compounds in water by purge and trap gas chromatography - method 503.1. Cincinnati, OH U.S. Environmental Protection Agency, Environmental Monitoring Systems Laboratory. 

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