The Atomic Emission Detector

Three different detection methods (gas chromatography with electron capture, mass spectrometric and atomic emission detectors) have been compared for the determination of polychlorobiphenyls in highly contaminated marine sediments [74], Only atomic emission detection in the chlorine-selective mode provided excellent polychlorobiphenyl profiles without interferences. However, the lower sensitivity of the atomic emission detector, compared to the other two detectors required a 10 to 20g sample size for most analyses. 

Lee SM, Wylie PL. 1991. Comparison of the atomic emission detector to other element-selective detectors for the gas chromatographic analysis of pesticide residues. J Agric Food Chem 39 2192-2199. 

The atomic emission detector is a tunable, element-specific detector that uses microwave-induced helium plasma to generate temperatures high enough to break molecular bonds. The generated free atomic species undergo electron excitation to higher energy states, followed by relaxation and photon emission at characteristic frequencies... 

One of the most attractive detectors for screening of CWC-related chemicals is the atomic emission detector (AED), which is capable of detecting selectively any element below the nanogram level. The... 

T.G. Albro and J. Lippert, Use of the atomic emission detector for screening and detection of chemical warfare agents and their breakdown products, in Proceedings of the 1994 ERDEC Scientific Conference on Chemical and Biological Defense Research., D.A. Berg (Ed.), National Technical Information Service, Spring-field, 171-176, 1996. 

F. David and P. Sandra, Comparison of the Sensitivity of the Flame Photometric Detector and the Atomic Emission Detector for the Analysis of Thiazone, Hewlett-Packard Application Note 228-136, Publication No. (43) 5091-1933E, USA, August 1991. 

Andersson, J. T., Polycychc aromatic sulfur heterocycles IV. Determination of polycyclic aromatic compounds in a shale oil with the atomic emission detector, J. Chromatogr. A., 693, 325-338, 1995 Thomson, J. S., Green, J. B., McWilliams, T. B., and Sturm, G. P., Analysis of Sulfur Compounds in Light Distillates, Symposium on Petroleum Chemistry and Processing, Chicago IL, 1995, pp. 696-698. 

Figure 3.24. Cutaway view of the atomic emission detector cavity block. (From ref. [363] Wiley-VCH).

Response characteristics of the atomic emission detector to different elements... 

In the atomic emission detector (AI D), the effluent from the OC column is introduced into a microwavc-induced plasma (MIP), an inductively coupled plasma (ICP). or a direct current plasma (DCP). The MIP has l)cen most widely used and is available commercially. TTie MIP is used in conjunction with a diode array or chargc coupled-device atomic emission spectrometer as shown in I igure27-I2. The plasma is sufficiently en-... 

Beside the qualitative identification of elements the atomic emission detector provides the possibility of determination of elemental composition and empirical formulas with compound independent calibration (Wylie et al., 1990 Quimby et al., 1995). This possibility enables an identification independent from retention times and does not require authentic reference standards for calibration. For structural elucidation the element ratios have been calculated using the method of relative response factors. Triphenylarsine was used as standard. The results have been confirmed by complementary high resolution mass spectrometric investigations. Table 4 summarizes the results of selected compounds. 

The detectors used in HTGC are, apart from the highly versatile flame ionization detector (FID), the phosphorus/nitrogen-selective alkali-flame ionization detector (AFID), the atomic emission detector, the inductively coupled plasma (ICP)-mass spectrometer, and, last but not least, mass spectrometers with electron impact and chemical ionization ion sources (EI/CI-MS). 

There are a number of other GC detectors commercially available. Photoionization detectors (PIDs) are primarily used for the selective, low-level detection of the compounds which have double or triple bonds or an aromatic moiety in their structures. Electrolytic conductivity detectors (ELCDs) are used for the selective detection of chlorine-, nitrogen-, or sulfur-containing compounds at low levels. Chemiluminescence detectors are usually employed for the detection of sulfur compounds. The atomic emission detectors (AEDs) can be set up to respond only to selected atoms, or group of atoms, and they are very useful for element-specific detection and element-speciation work. 

Sulfur compounds play a major role in determining the flavor and odor characteristics of many food substances. Often sulfur compounds are present in trace levels in foods making their isolation and quantification very difficult for chromatographers. This study compares three gas chromatographic detectors the flame photometric detector, sulfur chemiluminescence detector and the atomic emission detector, for the analysis of volatile sulfur compounds in foods. The atomic emission detector showed the most linearity in its response to sulfur the upper limit of the linear dynamic range for the atomic emission detector was 6 to 8 times greater than the other two detectors. The atomic emission detector had the greatest sensitivity to the sulfur compounds with minimum detectable levels as low as 1 pg. 

The following parameters were used for the atomic emission detector spectrometer purge flow, nitrogen 21/min. There was solvent back flush. Transfer line temperature was 250°C cavity temperature was 250°C water temperature was 65°C. Element wavelengths for sulfur, carbon and nitrogen were 181.4, 193.0 and 174.3 nm, respectively. 

Figure 5. Dynamic ranges of butyl mercaptan and phenyl sulfone on the atomic emission detector.

One of the latest developments in hyphenated techniques is the atomic emission detector. The availability of a bench-top model CGC -AED enables the use of this powerful technique in routine analysis. Detectabilities of this element-specific detector are of the order of 0.1 pg/s for organo-metallic compounds, 0.2 pg/s for carbon (more sensitive than FID), 1 pg/s for sulfur, and 15 pg/s for nitrogen, to mention only a few. The power of the technique lies in its supreme selectivity all elements can be detected selectively. As opposed to ECD, AED allows differentiation between var-... 

When gas chromatography is used to separate organometallic compounds, a number of detectors can be used. Conunon detectors such as Ihe FID, FPD, ECD, and MS have been employed. The most sensitive and selective detector for organometallic species is the atomic emission detector (113). The effluent from the GC enters a small chamber, and a microwave radiation is used to generate plasma. The intensity of the atomic emission radiation from the metal is monitored at a specific wavelength. Sometimes gas chromatography is interfaced with other instrumentation, such as atomic absorption spectrometry (AAS), inductively coupled plasma atomic emission spectrometry (ICPAES), inductively coupled plasma mass spectrometry (ICPMS), to detect the metal species. 

A recent extension of the scope of SPE-GC concerns the use of atomic emission detection. With its distinct element selectivity, the atomic emission detector can provide information that is complementary to that of a mass-selective detector. An additional advantage of AED is that the response per mass unit of an element is more or less independent of the structure of the analyte of interest. This allows the use of the universal calibration concept [90,91], although this statement is... 

Almost all GC methods for anionics involve use of the flame ionization detector. For added selectivity, a sulfur-specific detector may be used. For example, the flame photometric detector (8) and the atomic emission detector in sulfur-selective mode (20) have been demonstrated for use in quantifying LAS in mixtures. 

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