GC
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Gas chromatography can be used to quantitate various gases, complex organic molecules, metals, anions and pesticides in the lab or in the field Thomas A. Gosink University of Alaska Fairbanks, Alaska 9970 1
Chromatography is the most rapid and efficient technique for the separation of the components of any given system. It has been practiced for seven decades though it was not widely recognized until the forties. Gas phase chromatography, first developed in the fifties, has been applied to every aspect of analytical chemistry including application to the environment where it is currently being used for the analysis of the macro- to subpicogram quantities of various gases, complex organic molecules, pesticides and, more recently, some metals and anions. The number of organic compounds in the environment is very large, and it is in this area that a prima facie case exists for the use of gas chromatography either as a fingerprinting tool or as an integral part of the absolute identification of the species present. If any one method of instrumental analysis is to come close to truly universal applicability, it will be gas phase chromatography. Not only is it nearly universal in applicability, but it is rapid, usually on the order of minutes per sample; it is extremely sensitive, it can detect subnanogram (lo-') to subpicogram (lo-'*) quantities; and it is capable of reliably being used in the field. It is not advocated that gas chromatography will become the universal method of analysis. Among many other analyses, acidity measurements will still require pH meters, alkali metals will best be determined by atomic absorption and ultra-trace analyses of metals will best be performed by neutron activation methods. It is rare that any one technique, including gas chromatography (GC), can fully answer all aspects of an environmental problem. The researcher must make all attempts to remain aware of alternative methods that can compliment, though not necessarily replace, existing approaches to a problem. Numerous research papers exist on the application of gas chromatography to the environment. It is beyond the scope of this article to comment on even a small percentage of them. An attempt will be made, however, to indicate some of the important advances and how they directly apply to environmental analysis, or to suggest where they will be of importance to environmental chemists in the near future. Several recent articles of interest to environmental analysts appeared in the November 1973 issue of J. Chromatogr. Sci., and another that suggested standard referee GC methods in atmospheric hydrocarbon analysis appeared in the February 1974 issue.
rolysis patterns, or if a mass spectrometer is needed as the detector-analyzer [fnviron. Sci. Techno/. 8, 28 and 31 (1974)].McNair and Chandler have published an article [J. Chromatogr. Sci., Sept. 19731 dealing with available gas chromatographic equipment, and several other 1973 issues of that journal deal with supports and liquid materials (March and April) and detectors (May). The detector is a critical component of any GC system, and it principally determines the limit of detectability for any given substance. Approximately two dozen different kinds of detectors are available for GC analysis [Anal. Chem. 43, 113A (1971)l.Seven of the more common detectors are listed in Table 1, several of which are briefly discussed in this article. Caution is advised when looking at the sensitivities of GC detectors. The published values, as here, are best detectabilTABLE 1
Gas clrromatographlcdetectors DeIectaMmy Detector
(olmc)
Thermal conductivity
10-60
Despite the relatively low detectability of this system, it is probably the most widely used for virtually any kind of substance.
Flame ionization
10-12
Nearly a universal detector: however, many gases of interest to environmentalists give littie or no signal.
Alkali flame ionization
10-15
Tremendous sensitivity for phosphorus compounds (pesticides). Otherwise, limited to compounds of nitrogen, sulfur, and halogens.
Flame photometric
10-12
Limited application to phosphorus and sulfur compounds.
Electron capture
10-14
Hardware
Helium ionization
10-14
Gas chromatographs are probably the best buys for any type of analytical equipment available today, particularly in view of their diverse applications. Basic systems, quite useful in many aspects of environmental analyses, are available for less than $1000; but, the usual price range is around $3000-8000,which could include a small dedicated computer system in the readout. Indeed it would be hard to exceed $1 1,000-12,000total price for a complete gas chromatographic system, unless somewhat larger computers are needed as they are for the interpretation of complicated py-
Very useful despite its limited sensitivity to halogenated compounds and other electronegative atoms. A universal detector, but "limited" to low temperatures ( > V^II L U I I I eiiner ror ringerprinring wr w r me ieroy~r~y pletely identifying some or all of the individual components of a sample? Thomas A. Gosink is a visiting assoCiate professor at the Institute of Marine 5kience a t the University of Alaska, Fairbanks. Dr. Gosink's research to deV elop trace metal analysis 'n aqueous systems by using gas chromatographic niethods is funded under a National 5:cience Foundationgrant. Coordinated by LRE &
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