Detectors, in gas chromatography

Some of the important properties of a detector in gas chromatography are briefly discussed below. 

D F S Natusch and T M Thorpe, Element selective detectors in gas chromatography, Anal. Chem., 1973,45, 1184A... 

J. Sevcik, "Detectors in Gas Chromatography," Elsevier Scientific Publishing Co., Amsterdam and New York, 1975. 

Mass spectrometry (MS) is an analytical technique of great interest, one that provides structural information and quantitative data not easily obtained by other techniques. In view of these advantages, mass spectrometers have been widely used as detectors in gas chromatography however, adapting them for use with HPLC systems has been more difficult, because the sample is not in the gaseous phase and the solvent must be removed prior to ionization. These difficulties have been overcome by the development of a number of sample-introduction and ionization tech-... 

Sevcik, J., Detectors in Gas Chromatography, Journal of Chromatography Library, Vol. 4, Elsevier, Amsterdam, 1976. 

Lawson, A.E. and Miller, J.M., Thermal conductivity detectors in gas chromatography, J. Gas Chro-... 

The following data provide useful guidance in the operation and optimization of procedures with the gas density balance detector in gas chromatography.1 The property values were calculated with... 

R. Hall, The nitrogen detector in gas chromatography, part III, electrochemical detectors, CRC Crit. Rev. Anal. Chem., 7 345-363 (1978). 

The burner heads used in such cool flame emission studies are often simply quartz tubes. Figure 12 shows the burner system used by Arowolo and Cresser27 for automated gas-phase sulfide determination, for example. Other species determined by cool flame emission techniques include chloride, bromide, and iodide, which give intense emission in the presence of indium.29 The main application of cool flame emission techniques in environmental analysis is in speciation studies, for example for the separate determination of sulfite and sulfide, or as element-selective detectors in gas chromatography. 

TCD) detector or the flame-ionization (FID) detector, which are the two most common detectors in gas chromatography, respond to all (organic) compounds except the carrier gas. On the contrary, a selective detector responds to a range of compounds with a common physical or chemical property. Representatives of the latter group of detectors are the nitrogen-phosphorus detector (NPD), the electron capture detector (ECD), the mass selective detector (MSD) and - last, but not least - the tandem mass spectrometer (MS/MS). 

These data for successive scans are then stored for subsequent manipulation. The reconstructed total ion current trace, equivalent to that obtained from a flame ionisation detector in gas chromatography, shows the variation of total ion current with time and allows spectra of interest to be identified. A typical example is shown in Fig. 6A. The background may be subtracted to give clean spectra, and their identification may be attempted using libraries of standard spectra. If a composite spectrum is obtained from two unresolved peaks, complex subtraction routines may be used to obtain a pure spectrum of each of the components. These may be separately submitted for library searching. The spectra may then be plotted or obtained as a mass versus intensity listing. 

Mass spectrometers are used as detectors in gas chromatography offering the capability of compound quantitation and identification with exceptionally good sensitivity. For this reason, pyrolysis-gas chromatography/mass spectrometry (PY-GC/MS) is an excellent tool for polymer analysis. When a pyrolyser is used at the front end of the chromatograph, no special problems related to the GC/MS analysis are really added. 

The flame ionization detector (FID) is, by far, the most commonly used detector in gas chromatography (GC) and is probably the most important. It is a little uncertain as to who was the first to invent the FID some gave the credit to Harley and Pretorius [1], others to McWilliams and Dewer [2]. In any event, it would appear that both contenders developed the device at about the same time, and independently of one another the controversy had more patent significance than historical interest. The FID is an extension of the flame thermocouple detector and is physically very similar, the fundamentally important difference being that the ions produced in the flame are measured, as opposed to the heat generated. 

The use of capillary columns is a relatively recent advance in chromatography when compared with the thermal conductivity detector (TCD). The TCD is well established and is among the most commonly used detectors in gas chromatography. Some of the advantages of the TCD Include the simplicity, stability, and universal nature of the detector. 

Another non-photographic instrument for GED studies was build by Schafer and coworkers at the University of Arkansas in 1984 [24]. In this machine the scattered electrons are detected by a fluorescent screen, which is optically coupled to a custom multichannel analyzer. Later several improvements were introduced into the original design [25-27] and the possibility of using real-time GED as a detector in gas chromatography was demonstrated [28]. Some recent studies of SF [29] and Sep6 [30] show the application of this procedure. 

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