Focus treatment, resulting in better patient care. Cost of the in-office theophylline assay is estimated at just under $7 per determination, compared with up to $40 for the equivalent hospital test. Aside from the advantages of whileyou-wait testing, the new analyzers are financially attractive to doctors. The simplicity of the new techniques makes the analyzers very inexpensive to operate. Greater pressure for health care cost containment and the fact that many insurers will now pay only for the least costly manner of health care (many Blue Cross member plans provide financial incentives for the performance of more in-office procedures) are factors that will tend to keep the number of small analyzers found in doctors' offices on an upward curve. The in-office analyzers would not have gained much acceptance if their precision and accuracy had not compared favorably with the traditional liquid reagent analyzers used in most hospitals. But the performance of dry reagent chemistries has been shown to be comparable to the more established procedures (2). When representative assays from both the Ames and the Kodak analyzers were compared to their traditional counterparts, correlation coefficients were all greater than 0.99. Now that clinical analyzers are in the office, what next? The increasing emphasis on "wellness" is causing more and more people to monitor their own health at home. In a recent review on self-testing, Alfred and Helen Free of Miles Labs point out that many chemical assays are already available for the home user, including tests for glucose, ketones, and many other analytes (3). Diabetics have been monitoring their own blood sugar levels using dry reagent strips for years. Many women now do home pregnancy tests before they go to see their doctors. A new home test for breath alcohol is giving drinkers a way to check their ethanol level before they drive. And new home tests are being developed for cholesterol and venereal diseases such as syphilis and herpes. As more new assays are developed patients will increasingly be able to take better care of themselves with the assistance of their doctors. M.D.W. References (1) Walter, B. Anal. Chem. 1983,55, 498514. (2) Hendeles, L.; Weinberger, M. Immunol. Allergy Pract. 1984, 6, 53-59. (3) Free, A. H.; Free, H. M. Clin. Chem. 1984, 30, 829-38.
Electrochemistry Faces Reality "Ten years ago, electrochemistry [EC] was really not very relevant to chemical analysis," said Larry R. Faulkner provocatively at a recent symposium. "At that time, the practical application of electrochemistry to real analytical problems was sorely lacking." According to Faulkner, most analytical chemists would have attributed a host of deservedly unattractive characteristics to the electroanalytical chemistry of the early 1970s: • EC techniques were slow, messy, and cumbersome. Many of them were oriented to the dropping mercury electrode (DME), which, said Faulkner, "nearly everybody finds cumbersome." • There were problems associated with electrode fouling, particularly in complex matrices such as in biological samples. • EC scans exhibited a very low peak capacity—at best, only a few analytes could be determined simultaneously. "The width of a voltammetric peak is thermally determined," explained Faulkner, "and there's nothing you can do about it." • Sensitivity was often unspectacular. • There was little commercial equipment available, and what was available tended to be unsophisticated. • Electrochemical techniques were very labor intensive and generally incompatible with automatic sampling. Fortunately, EC began to face reality in the early 1970s—the reality of dealing with complicated samples. "We've come a long way since then," said Faulkner,"and what we can see ahead is really dramatically different from what we see in the past." Faulkner, a professor at the University of Illinois, was speaking at a symposium arranged by Jeanette G. Grasselli of Sohio and held to celebrate the tenth birthday of the Federation of Analytical Chemistry and Spectroscopy Societies (FACSS). The FACSS meeting was held in Philadelphia in late September 1984. LCEC According to Faulkner, one dramatic new approach that has had a significant impact in the past decade is liquid chromatography-electrochemistry (LCEC), pioneered by Peter Kissin-
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ger, a professor at Purdue University and president of Bioanalytical Systems Inc. (BAS). LCEC, in which a separation step precedes electrochemical analysis, was an extremely important development, in that it allowed EC to address complex matrices for the first time. This approach has been so successful, said Faulkner, "that there's probably a vastly larger number of electrochemical assays being
Instruments have been so complicated to operate that only specialists could operate them. carried out by LCEC than essentially any other method at this time." SMDE A significant improvement in electrode design in the past decade was the development of the static mercury drop electrode (SMDE) by EG&G Princeton Applied Research Corporation (EG&G PARC). According to Faulkner, the SMDE gets rid of the time dependence in electrode area and is therefore an "extremely important improvement" over the DME, whose electrode area changes continuously in the course of an experiment. Cybernetic instrumentation A major problem in EC until very recently was the need to have multiple setups to accommodate the multiplicity of electrochemical experiments. According to Faulkner, "Instruments have been so complicated to operate that only specialists could operate them." But the past five years have seen the development of advanced instrumentation that does not need to be reconfigured for each experiment, instrumentation with microprocessorcontrolled access to a repertoire of different electrochemical techniques (i). Faulkner played a major role in the
Focus
'The possible applications of modified electrodes are staggering. design of a cybernetic (intelligent) instrument, marketed by BAS, that makes it easier to perform a wide range of electrochemical experiments. Electrochemical instruments designed to be multifunctional through software control rather than hardware reconfiguration are also currently available from EG&G PARC and Sargent-Welch. Uliramicroelectrodes The impetus for Mark Wightman's (Indiana University) pioneering work on ultramicroelectrodes was his interest in monitoring chemical species in rat brains with reasonable spatial definition and without having to disturb the system any more than necessary (2). As it happens, ultramicroelectrodes have a number of other characteristics that are very attractive, including the following: • They are capable of producing signals that are less subject to interference than other types of electrodes, particularly in fast time scale experiments. • Since they are so small, they draw extremely small amounts of current, frequently in the range of picoamperes. This ameliorates the uncompensated iR drops in the solution (where i represents current and R represents resistance) that frequently cause distorted peak shapes and other problems. "If i is extremely small," explained Faulkner, "it matters not if R is large. The problem of uncompensated resistance is not the R, it's the iR." • Ultramicroelectrodes make it possible to do EC on a nanosecond time scale. This domain was previously inaccessible due to capacitance problems. • Ultramicroelectrodes have also made it possible to do electrochemical experiments in media such as benzene, hexane, frozen acetonitrile, and water ice. These media cannot be used in conjunction with conventional electrodes. "So I think ultramicroelectrodes have a very bright future, and we're just on the cutting edge of seeing what they can do," said Faulkner. "If they ever become commercialized—and I
think they will—they will bring electrochemistry into applications areas it was never able to address before." Modified electrodes The area of modified electrodes or tailored surfaces is "receiving a tremendous amount of attention right now," said Faulkner. The basic idea is to place a chemical or a coating on the surface of an electrode to modify its response capabilities. The interest might be in electrocatalysis—producing an electrode surface able to oxidize or reduce a species that, for kinetic reasons, will not oxidize or reduce on a normal surface. Or the interest might be in creating a preconcentrating layer—bringing something in from solution, sequestering it on the electrode, and then determining it with a voltammetric scan. "The possible applications of modified electrodes are staggering," Faulkner said. "They could be useful in power sources, electrosynthesis, infor-
mation display, and specially designed sensors." What are we going to see in the future? According to Faulkner, we'll see: • smarter instruments, • tailored surface-modified electrodes, • disposable electrodes, perhaps fabricated with microelectronics techniques, and • electrochemical array detectors. "In the end—and this is sort of science fiction—I think one can envision a system that would involve electrochemical measurement coupled to a telemetric apparatus. One could then do electrochemical sensing in inconvenient locations, such as interior body locations," Faulkner concluded. References (1) He, Peixin; Avery, James P.; Faulkner, Larry R. Anal. Chem. 1982,54, 1313-26 A. (2) Wightman, R. Mark. Anal. Chem. 1981,53,1125-34 A. S.A.B.
Blueprintfora New X-rav Detector L. S. Birks, recently retired from the Naval Research Laboratory, challenged analytical chemists to discover a new X-ray fluorescence (XRF) spectrometric detector in a talk he presented at the FACSS tenth birthday symposium (see related story above). Birks's challenge might easily be dismissed as pure speculation, but something that happened back in the 1950s indicates that there could be more to his proposal than immediately meets the eye. At that time, the gas-filled proportional counters and scintillation counters that had recently been invented for XRF were first becoming popular. The problem with these detectors is that it takes about 20 eV (proportional counters) and about 50 eV (scintillation counters) of X-ray energy to generate each useful electron in the active material of these detectors. This parameter is referred to as the detector's effective ionization potential. At an American Society for Testing and Materials (ASTM) meeting about that time, Birks presented a paper in which he said that another detector was needed, one that would require only 3-4 eV per event rather than 20
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or 50 eV per event. That was pure speculation at the time, but within a few years the now very popular lithium-drifted silicon [Si(Li)] semiconductor detectors (with an effective
When we needed better resolution than the gas proportional counters could provide, people went out and discovered the Si(Li) detector. Now we need to go the next step.
ionization potential of only about 3.8 eV) had been invented. This low effective ionization potential makes the Si(Li) detector a much higher resolution device than its two predecessors. "That was kind of a wild guess," says Birks of his ASTM talk. "It's for-
