Analysis by gas chromatography

Gas chromatography (GC) is the most common and successful method of soil-gas analysis. The detection limits are about 1-10 ppb by volume. The basic components of a gas chromatographic system are a carrier gas and a flow control system, a column packed with a gas-separating material, an oven for temperature control of the column, a sample introduction device, a detector and a recording system (Fig. 8-8). 

In the operation of a GC system, a gas mixture is injected onto the column and is carried through the column and detector by the carrier gas at a specific flow rate and temperature (either a constant temperature or a reproducibly programmed temperature range). The components of the gas mixture pass through the column at different rates, and 

Various commercially-packed columns and packing materials are available and have been used for the separation and analysis of mixtures of sulphur gases (Bremner and Banwart, 1974 De Souza et al., 1975 Supelco, 1977). The most commonly-used columnpacking materials for sulphur-gas analysis are Chromosil 310, acetone-washed Porapak-QS and three types of Carbopak B. Selection must be based on the analytical data desired. Each of these packings separates different components and has advantages and disadvantages. 

Column packings for gas chromatographic determination of sulphur gases 

Column packing material Sulphur gases separated Disadvantages 

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The compound was obtained from Cities Service Research and Development Co, Petrochemical Development Department, Sixty Wall Tower, New York 5, New York. Analysis by gas chromatography showed it to be pure, and it was used without further purification. 

Analysis by gas chromatography shows the acid to be pure (column as in Note 8), retention time 4j minutes at 175°. 

Other fluorinated derivatives of acetylacetone are trifluoroacetylacetone (CF3COCH2COCH3) and hexafluoroacetylacetone (CF3COCH2COCF3), which form stable volatile chelates with aluminium, beryllium, chromium(III) and a number of other metal ions. These reagents have consequently been used for the solvent extraction of such metal ions, with subsequent separation and analysis by gas chromatography [see Section 9.2(2)]. 

The number of reported applications to analytical determinations at the trace level appear to be few, probably the best known being the determination of beryllium in various samples. The method generally involves the formation of the volatile beryllium trifluoroacetylacetonate chelate, its solvent extraction into benzene with subsequent separation and analysis by gas chromatography..61... 

J Novak, Quantitative Analysis by Gas Chromatography, Marcel Dekker, New York, 1975... 

The symposium upon which this volume is based was organized at a turning point in nitrosamine research. Almost all types of commercial products have been tested for volatile nitrosamines, and there have been a number of outstanding accomplishments of combined university-gov-emment-private industry actions to lower or eliminate volatile nitrosamines in those products found to be contaminated. However, there is still a major gap of knowledge with regard to compounds that are not amenable to analysis by gas chromatography, and this is clearly a frontier of current research. There are also many important questions regarding chemistry, mechanism of action, and relation to human disease whose answers lie in the future of research in this field. 

Friedrich Helfferich and Gerhard Klein Quantitative Analysis by Gas Chromatography, Josef Novak High-Speed Liquid Chromatography, Peter M. Rajcsanyi and Elisabeth Rajcsanyi... 

Quantitative Analysis by Gas Chromatography, Second Edition, Revised and Expanded, Josef Novak... 

Analytical methods for parent chloroacetanilide herbicides in soil typically involve extraction of the soil with solvent, followed by solid-phase extraction (SPE), and analysis by gas chromatography/electron capture detection (GC/ECD) or gas chromatog-raphy/mass spectrometry (GC/MS). Analytical methods for parent chloroacetanilides in water are similarly based on extraction followed by GC with various detection techniques. Many of the water methods, such as the Environmental Protection Agency (EPA) official methods, are multi-residue methods that include other compound classes in addition to chloroacetanilides. While liquid-liquid partitioning was used initially to extract acetanilides from water samples, SPE using... 

Transfer the concentrate into a 200-mL separatory funnel using two portions of 20 mL of n-hexane. Add 100 mL of saturated sodium chloride aqueous solution and extract twice with 100 mL of n-hexane by shaking for 5 min and allow the phases to separate. After dehydration of the n-hexane extract with 10 g of anhydrous sodium sulfate, concentrate the extract to dryness below 40 °C with a rotary evaporator. Transfer the residue with three portions of 5 mL of n-hexane into a glass column containing 10 g of Florisil (deactivated by water at a rate of 1%). Elute with 100 mL of n-hexane-ethyl acetate (9 1, v/v) and then with 100 mL of n-hexane-ethyl acetate (7 3, v/v). Concentrate the second eluate to dryness and dissolve the residue in 10 mL of n-hexane and analysis by gas chromatography/flame thermionic detection (GC/FTD). 

The most general method for the simultaneous analysis of oxyanions by gas chromatography is the formation of trimethylsilyl derivatives. Trimethylsilyl derivatives of silicate, carbonate, oxalate, borate, phosphite, phosphate, orthophosphate, arsenite, arsenate, sulfate and vanadate, usually as their ammonium salts, are readily prepared by reaction with BSTFA-TMCS (99 1). Fluoride can be derivatized in aqueous solution with triethylchlorosilane and the triethylfluorosilane formed extracted into an immiscible organic solvent for analysis by gas chromatography [685). 

As a more sensitive detection method, MS can be very useful in amino acid determinations. For example, S-carboxymethyl-(R) cysteine or SCMC, is a mucolytic agent used in the treatment of respiratory diseases. The development of a method utilizing high performance IEC and atmospheric pressure ionization (API) mass spectrometry to quantify SCMC in plasma has been described.66 This method is simple (no derivatization needed), rapid (inn time 16 min.), sensitive (limit of quantification 200 ng/mL in human plasma), and has an overall throughput of more than 60 analyses per day. API-MS was used successfully with IEC to determine other sulfur-containing amino acids and their cyclic compounds in human urine.67 IEC has also been used as a cleanup step for amino acids prior to their derivatization and analysis by gas chromatography (GC), either alone or in conjunction with MS.68 69... 

Purdon JG, Pagotto JG, Miller RK. 1989. Preparation, stability, and quantitative analysis by gas chromatography and gas chromatography-electron impact mass spectrometry of tert-butyldimethylsilyl derivatives of some alkylphosphonic and alkyl methylphosphonic acids. J Chromatogr 475 261-272. 

Stirring was initiated, and the autoclave was heated to 400°C which required 90 minutes for E10 and 100 minutes for El9. The temperature was maintained at 400°C for 1 hour, then lowered to room temperature. The cooling duration to 300°C was 5 minutes for E10 and 40 minutes for El9. Stirring was terminated at room temperature. Gaseous products were removed for analysis by gas chromatography coupled with mass spectrometry (GC-MS). The reaction products were distilled at reduced pressure to remove the spent donor solvent mixture, and the remaining coal products were solvent fractionated. 

For many of the organic materials in seawater, some form of chemical pretreatment is necessary before analysis is possible. The obvious cases are the hydrolysis of polysaccharides and proteins before the analysis for monomeric constituents, and the formation of volatile derivatives to permit analysis by gas chromatography. These methods will be discussed further in Chap. 9. 

You have the task of purchasing some n-hexane for use in three different applications (i) pesticide analysis by gas chromatography, (ii) as a solvent to extract some non-polar high-boiling (200-300°C) oils from a soil sample, and (iii) as a mobile phase for HPLC analysis with UV detection. List and contrast the performance characteristics you need to take into account for purchasing the appropriate grade of hexane in each case. n-Hexane boils at about 70°C. Will any of your choices of hexane be suitable for use for HPLC analysis with fluorescence detection Explain your decision. 

A rapid and simple method for PBDE and HBCD determinations in sediment and fish samples was used. The analytical method was based in selective pressurized liquid extraction (SPLE) [21] without further cleanup step and analysis by gas chromatography coupled to mass spectrometry (GC-MS), working with negative ion chemical ionization (NCI) [22, 23],... 

Analysis of pesticides (eight in total, namely, molinate, propanil, fenitrothion, malathion, bentazone, cypermetrine, maloxon, and fenitrothion oxon) in biota was accomplished with a method based on pressurized liquid extraction (ASE), followed by SPE clean-up, and analysis by gas chromatography-mass spectrometry with electron impact ionization (GC/MS-EI). 

Spectrophotometric determination with 4-hexylresorcinol and a fluorometric method with m-aminophenol are the most commonly used procedures for the determination of acrolein. However, gas chromatography and high-performance liquid chromatography procedures are also used (USEPA 1980 Kissel etal. 1981 Nishikawa and Hayakawa 1986). Acrolein concentrations in rainwater between 4 and 200 pg/L can be measured rapidly (less than 80 min) without interference from related compounds the method involves acrolein bromination and analysis by gas chromatography with electron capture detection (Nishikawa and Hayakawa 1986). Kissel etal. (1981) emphasize that water samples from potential acrolein treatment systems require the use of water from that system in preparing blanks, controls, and standards and that acrolein measurements should be made at the anticipated use concentrations. 

In order to understand the removal of FMs during wastewater treatment, it is necessary to measure these compounds throughout the wastewater treatment process. Because of the complex nature of wastewater matrices and the low concentration of FMs (0.001-60 pg/L) [11] throughout the treatment plant, accurate and sensitive analytical methods have been developed by a number of researchers. Fortunately, the analytical techniques developed to measure traditional SOCs, such as solvent extraction, extract concentration, and analysis by gas chromatography-mass spectrometry, in general also apply to FMs. 

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. 

Thuren [1] determined phthalates in sediment using solvent extraction (acetonitrile, petroleum ether), clean-up with deactivated Florisil, and quantitative analysis by gas chromatography. The detector response was linear between 0.5 and lOOng. The detection limit (signahnoise ratio 2 1) was O.lng for dimethylphthalate, dibutylphthalate and di(2-ethylhexyl) phthalate, and 0.05ng for benzoylbutylphthalate. Recovery was between 30% and 130% depending on the ester. Low recovery for dimethylphthalate (30%) was probably due to pyrolysis in the detector (detector temperature was 320°C). 

The solvent extraction of chlorinated pesticide residues from soil is often achieved by using mixtures of solvents such as hexane-isopropanol or hexane acetone, but can be unsatisfactory owing to the emulsification problems [2, 3] or, with hexane-isopropanol, poor recovery [2, 4], Acetone extraction of soil is efficient [4, 5] but problems can arise from large amounts of coextracted material unless an efficient clean-up technique [6] is used prior to analysis by gas chromatography. 

Cyperquat, a post-emergence herbicide has been determined in surface soil by a method involving catalytic hydrogenation to l-methyl-4-cyclohexypiperdine and analysis by gas chromatography-mass spectrometry. Recovery of cyperquat from fortified soil samples was 77% at the 0.5mg kgy1 level and 85% at the lmg kgy1 level [213]. 

We mentioned in Chapter 2 (Section 2.6.1) that a purge-and-trap procedure sometimes precedes an analysis by gas chromatography. An example of this procedure is found in the City of Lincoln, Nebraska, Water Treatment Plant Laboratory. Water treatment includes chlorination. When water is chlorinated, chlorine reacts with organic matter to form trihalomethanes (THMs), such as chloroform, bromoform, bromodichloromethane, and chlorod-ibromomethane. THMs in water are regulated by the Safe Drinking Water Act, and so the laboratory must analyze the treated water to determine their concentration. 

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