the ANALYTICAL C H E M I S T R Y bian-
nual reviews. Taking the ICP citations as the base, there are only 20-30% that many MIP papers, and only 10-20% that many DCP papers. The number of DCP papers is as high as it is as a result of the recently established biennial Winter Plasma Conference. The size of the data base is an indication that more people know more about ICPs than MIPs and DCPs combined. Level of development. The DCP has been commercially available for a longer period of time than the ICP. A dc plasma jet was available in the early 1950s. Even the most recent version of DCP has been around longer than most of the ICPs. As characterized by the data base material, however, the ICP has been described more extensively at a fundamental level. There are numerous papers describing microwave devices, but very few report on any single, specific configuration. Consequently, the theoretical development of the MIP is still fragmented. The theoretical treatment of the DCP is only now starting to appear. Some recent DCP papers have examined the DCP in the sort of detail with which the ICP has always been reported. From a practical point of view, characterized by the type of tinkering that results in physical alterations to the source or its power supply, not much has been done with the DCP. This is probably because there is only one version available. Without a second or third variation on the theme, very little curiosity has been shown about how the device might be rearranged. Further, the DCP provides little to be adjusted in normal operation. So the device does not lend itself to inventive tweaking that might indicate the diversity of modifications from which it could benefit. The ICP has evolved through many stages of development; it continues to do so. Some of the latest practical developments involve lower power, lower argon usage, and different support gases. The MIP probably offers the greatest opportunity for configuration development. Except for the TMoio cavity, no single variation of MIP has become widely accepted. With regard to sample introduction, there are more versions of sample input device for the ICP than for DCPs and MIPs. The MIP is interfaced best to a capillary column gas chromatograph; it requires quite a bit of development for direct solution input. The sample introduction device used on the DCP is reasonably effective considering it wasn't developed for that purpose originally. The DCP sample introduction scheme could use much more development. The MIP has yet to find a consistent need in plasma AES. It is an an-
swer looking for a problem. Even for the halogen detection with which it does so well, adequate demand does not exist to warrant commercial development of an MIP system at this time. The DCP provides a less expensive, more operationally forgiving source for plasma AES. It is easy to run and maintain. And it is an exceptionally clever optical match to the échelle spectrometer to which it has always been mated. It suffers from lack of a wider interest base among the publishing research community and its unwarranted connection to dc arc technology. The ICP is the de facto standard source of plasma AES. It may not be the best. But there are more of them around. And all the latest, hottest work is being done with them. Suggested reading Inductively coupled plasmas Fassel, V. A. Science 1978,202(13), 183. Barnes, R. M. CRC Crit. Rev. Anal. Chem. 1978, 7. Thompson, M.; Walsh, J. N. A Handbook of Inductively Coupled Plasma Spectrometry; Chapman and Hall: New York, 1984. Direct current plasmas Miller, M. H.; Eastwood, D.; Schulz-Hendrick, M. Spectrochim. Acta 1984,39B, 13. Zander, A. T.; Miller, M. H. Spectrochim. Acta 1985,40B, 1023. Miller, M. H.; Zander, A. T. Spectrochim. Acta 1986,41B, 453. Microwave-induced plasmas Zander, A. T.; Hieftje, G. M. Appl. Spectrosc. 1981,35(4), 357. Matousek, J. P.; Orr, B. J.; Selby, M. Prog. Analyt. Atom. Spectrosc. 1984, 7, 275.
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800-621-0851 Ext. 204 Andrew T. Zander is a senior staff engineer at Perkin-Elmer, working in analytical instrumentation development. He holds a B.S. degree in chemistry from the University of Illinois and received a Ph.D. in analytical chemistry in 1976 from the University of Maryland. He held a postdoctoral appointment at Indiana University, spent two years on the faculty at Cleveland State University, and was an application engineer with Spectrometries, Inc., prior to his present position. His research interests center on radiation sources for atomic spectrometry, diffraction devices, and signal detection and processing schemes.
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ANALYTICAL CHEMISTRY, VOL. 58, NO. 11, SEPTEMBER 1986 · 1149 A
