FOCUS amperometric detection methods. The electrode surface can be cleaned between actual current measurements. Joseph Wang, from New Mexico State University, discussed biocatalyst-modified amperometric electrodes for detection in flowing streams. According to Wang, membranes for size or charge exclusion enhance the selectivity and stability of the electrodes. Cellulose acetate, polyaniline, and polyphenol coatings provide the desired size exclusion effect, whereas charged poly(4-vinylpyridine) or Nafion coatings are used for appropriate charge exclusion. Multifunctional operation (selectivity, catalysis, protection, etc.) is obtained with a multilayer or composite (mixed) electrode coating. Some specialized applications of EC detectors were also described. Gyorgy Marko-Varga, from the University of Lund in Sweden, analyzed fermentation broth sugars using postcolumn, coimmobilized enzyme reactors and modified electrodes; and José Lima from the University of Oporto in Portugal discussed a tetraoctylammonium barbiturate-based PVC potentiometric detector for FIA that is sensitive to barbiturate ions. Ultraminiaturized detection for microcolumn HPLC or CE methods was reviewed by Hans Poppe from the University of Amsterdam. A key consideration for these detectors is the smallest volume needed for detection, because that ultimately dictates the absolute detection limit and how far miniaturization can be taken. Poppe described a number of miniaturized systems for detection on the nanoliter scale, including liquid-liquid extraction, sheath flow reactor, enzyme-moderated reaction, and electrochemical systems. Additional detection power, through on-line derivatization, was illustrated for heterogenous systems. Gary Christian and Jaromir Ruzicka, both from the University of Washington, reported on optosensing in FIA using the reversible sorption of hydrophobic reagents and analytes onto hydrophobic particles to selectively measure analytes. They described a porous, hydrophobic membrane detector that allows gases to diffuse (eg., NH 3 , HC1) but blocks passage or detection of nongaseous species such as NaOH. The gases are detected by the changing color of an indicator incorporated into the membrane. The implications of the complementary nature of FIA and HPLC (3) were presented. New polymeric reagents for off- and on-line derivatization of nucleophiles were described by Ira Krull. Solidphase, heterogenous derivatization leads to improved specificity and sensi-
Still using these tools tivity in HPLC, regardless of detection mode. KrulFs group has designed a mixed-bed, solid-phase reactor containing three different tagging reagents, thereby leading to three derivatives with different chromatographic and detector properties. A novel approach was described for off- and online tagging of enantiomeric amines for Pirkle-type chiral separations. In the future, according to Krull, all approaches to chiral recognition in HPLC should be possible via single or mixedbed type polymeric reagents. Several hyphenated techniques were also presented. Richard Browner from the Georgia Institute of Technology discussed the idea of using a particle beam (MAGIC) interface with HPLC/ FT-IR. In his system a vapor aerosol of analyte particles is deposited on a salt disk/plate and rotated into the FT-IR beam. It appears that this new approach for LC/FT-IR interfacing may have some significant advantages over current practices. Julian Tyson described detectors for atomic spectrometers. Because these spectrometers either operate intermittently (electrothermal atomizers) or produce a steady-state signal (nebulizers for flames or plasmas), some form of on-line chemistry will probably be needed to improve FIA and atomic spectrometry detection limits. Alternatively, nebulizers and spray chambers will have to be specifically designed for use with FIA introduction. According to Tyson, the single-well stirred tank model indicates that there should be some benefit from designs with reduced spray chamber volumes. Some particularly relevant research by the symposium's organizers presented the dual use of an FIA manifold as a screening system and postcolumn reactor-detector in HPLC. Valcarcel and Luque de Castro exploited the rapid measurement frequency of FIA for screening large numbers of samples for total analyte content—in this case, toxic substances. Only elevated samples are then subjected to time-consuming chromatography, employing the same FIA configuration as a postcolumn reactor-detector. Most of the participants acknowledged the high scientific level of the meeting and left Cordoba with the hope for future meetings on the same subject. The seed has been planted. References (1) Denkert, M.; Hackzell, L.; Schill, G.; Sjogren, E. J. Chromatogr. 1981,218, 31. (2) Arvidsson, E.; Commen, J.; Schill, G.; Westerlund, D.; J. Chromatogr. 1989,461, 429. (3) Ruzicka, J.; Christian, G. D. Analyst, in press.
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