Editors' Column
AdvancedAnalytical c o n c e p t s for the Clinical Laboratory The road to Gatlinburg, Tenn., was well traveled this year thanks to the 225 clinicians and chemists who gathered there on April 21-22 for the 15th Annual Symposium on Advanced Analytical Concepts for the Clinical Laboratory. This year's symposium clearly lived up to its reputation as an important forum for workers in all phases of clinical research and development to discuss new developments on the forefront of clinical chemistry. As its name suggests, the symposium focuses on analytical methods that may one day find a place in the clinical laboratory. In the future, we may see the inductively coupled plasma, photoelectroanalytical chemistry, optical-fiber fluoroprobes, and laserenhanced ionization being used routinely in the clinical laboratory. While reports such as these proposed new concepts in clinical analysis, other papers presented at the symposium focused on already existing clinical methodology. Eighteen papers were presented in three half-day sessions. The first two sessions were entitled Analytical Concepts and Analytical Systems, respectively. The third and final session— the highlight of the symposium—was devoted to Advanced Spectroscopy. In the Analytical Concepts session, Mel Kronick of Applied Biosystems reported on an immunoassay technique involving the use of fluorescent dyes called phycobiliproteins. The dyes, which can be isolated from a
wide variety of algae, can be linked to antibodies or other specific binding proteins using conventional crosslinking reagents. The advantages of using these dyes in immunoassay systems are enhanced sensitivity, decreased nonspecific binding, and decreased background fluorescence. The next paper in the session, presented by A. S. Janoff of the Liposome Company, described the use of liposomes in a colorimetric assay for systemic lupus erythematosus. A cationresponsive red dye is entrapped within the liposome, a lipid bilayer that closes in on itself to form an inner compartment. In dilutions of normal sera, the liposome membranes undergo a rearrangement upon addition of divalent cations, resulting in release of the entrapped dye and the rapid formation of a blue cation-dye complex. In sera of patients with active lupus, however, the liposomes are selectively stabilized, so that they remain intact in the presence of added divalent cations and maintain their red color. Because the assay requires only 1-min incubations and can be performed on standard microtitre plates, it can be used for screening a large number of samples in a short period of time. At present, there are no methods suitable for mass screening for cystic fibrosis, a genetically transmitted disease affecting one in 1500 newborn Caucasians. However, because of the work of E. J. Fogt and colleagues at Medtronic, Inc., mass screening for
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cystic fibrosis may soon be a reality. Fogt's method is based on determining if concentrations of sodium chloride in sweat are abnormally high, a characteristic sign of cystic fibrosis. After sweating is induced in the patient's skin, a patch is applied that collects approximately 50 ML of sweat and visually indicates whether chloride concentration is greater than the normal value. The patch consists of a center "blanking" circle and an outer "indicating" ring. Sweat enters the patch at the center and diffuses radially outward. All chloride present in excess of the normal range is carried outward to the indicating ring, where it reacts and changes the brown ring's color to white. A tab at the outer edge of the indicating ring shows when the test is completed. The method is now being clinically evaluated. In contrast to the above reports, the papers in the Advanced Spectroscopy session described techniques that are much further away from actual clinical application. Nevertheless, the session served the vital purpose of bringing together the researchers who develop new analytical methods and the clinical chemists who may one day apply these methods to real-life problems. Gary Hieftje of Indiana University led off the session by describing a new microsampling technique. Hieftje's microdroplet-generating system, the heart of which is a needle that "pokes" into the liquid sample, is capable of distributing a total volume (continued on p. 822 A)
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Editors' Column of 1 μL· in the form of 1000 identical aliquots. Hieftje also described a new variation on ion chromatography, which he called "replacement" ion chromatography. Cations are first sep arated as in conventional ion chroma tography. After passing through a sup pressor column, the effluent flows through a column containing lithium ions, where the sample ions are "re placed" by the lithium ions. These lithium ions can then be detected by flame photometry. A similar proce dure can also be applied to anions. Unlike conventional conductometiric detection, the method offers potential sensitivities in the sub-ppb range and a useful operating range up to 105. According to Stephen Weber of the University of Pittsburgh, photoelectroanalytical chemistry (PEAC) is so new a technique that reports of it have not yet appeared in the analytical lit erature. PEAC is based on electro chemical detection of light-generated species and combines the advantages of catalytic activity at an electrode surface with photosensitivity. The method has potential applications in techniques involving labeling, such as immunoassay and chromatographic detection. Weber and co-workers have achieved detection limits of 5 X 1 0 - 1 1 M in clean solutions and are currently determining the limit of de tection in human serum. Thanks to recent developments in laser and fiber-optic technology, in vivo analytical measurements are no longer an impossibility. M. J. Sepaniak of the University of Tennessee— Knoxville described the use of microscale fluoroprobes for the measure ment of drugs in a number of biologi cal matrices, including in vivo mea surements in laboratory mice. Other papers presented in the Advanced Spectroscopy session were devoted to topics such as multiwavelength meth ods, trace metal determinations by laser-enhanced ionization spectrome try, and element-selective inductively coupled plasma detection. This year's symposium was once again sponsored by Oak Ridge Nation al Laboratory (ORNL) and the Ameri can Association for Clinical Chemis try, with support from Instrumenta tion Laboratories, Eastman Kodak, and the Ames Division of Miles Labo ratories. According to chairman Carl Burtis of ORNL, symposium organiz ers are considering nearby Knoxville for the site of next year's meeting. As in past years, most of the papers presented at the symposium will be published in the September issue of Clinical Chemistry. Marcia S. Vogel
