Focus
New Directions in Analytical Chemistry The future is a funny thing. Sometimes it's hard to figure out whether it's far away or already here. Judge for yourself how long we will have to wait for the future of analytical chemistry as you review the conversation Bruce Kowalski of the University of Washington recently had with his computer. Kowalski (BK): [Log in]. Computer (COMP): Good morning. Who are you and where do you keep your money? BK: Bruce Kowalski, real estate. COMP: Very funny, Bruce, but I need your computer account number. [Types in his account number. It's a very long number, about 40 digits.] COMP: You have a good memory. For a human. Now your wish is my command. BK: Connect me with the separations lab computer. COMP: I know what it knows. BK: Were my 7422 river samples run
last night automatically? COMP: Natiirlich. Would you like to see the complete organic analysis results? You'll need two hours to read the listing. BK: No. Did any of the samples have components from the EPA list? COMP: Yes, the sediment cores from sector SS4 had PCBs above 1 ppm. Those results are on your printer. Have you checked? BK: It's early. COMP: Next command please. BK: I'm going to the metals analysis lab. I'll need your help there. COMP: See you later. BK, on another terminal: Hi. Bruce again. COMP: Before you begin, you should know that I've shortened GC runs by an extra 32.4%. Your new GC/MS mathematical resolution algorithm can completely resolve effluent peaks with up to 10 components, so there is no need to separate further. We should publish this. BK: We? [Logout].
The Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy started on an exciting note Monday morning, March 9, with a symposium on "New Directions in Analytical Chemistry," organized and chaired by Henry Freiser of the University of Arizona. The above conversation of Bruce Kowalski with his computer was part of his presentation on analytical chemistry as an information science, and other leading analytical chemists made presentations on the future prospects in their respective fields: Allen Bard on electroanalytical chemistry, Calvin Giddings on separation science, Bonner Denton on spectroscopy, and Richard Van Duyne on surface chemistry. In the following pages, A N A L Y T I C A L C H E M I S T R Y has
summarized their visions of the future. Of course, the reader may disagree about the relative importance of the various predictions made by the experts in this symposium. Bonner
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Denton thus recommended that his concept of the "variable constant" be used to grade the concepts expressed. To apply the variable constant, Denton explained, multiply any concept you agree with by some very large factor. Any concept you disagree with may be multiplied by a factor of zero; it thus will drop out and cease to exist. Electroanalytical Chemistry "The Renaissance in Polarographic and Voltammetric Analysis" by Jud Flato ( A N A L Y T I C A L C H E M I S T R Y ,
1972, 44, 75-87 A) is required reading for graduate students of electroanalytical chemistry. But according to Allen Bard of the University of Texas, "People talk about a renaissance, but I don't think the baby was ever dead." If electroanalytical chemistry has undergone a renaissance in the past 10-20 years, explains Bard, it must be ascribed to three elements:
• Instrumentation. Not so much digital instrumentation, which came in later and played an important role, but the lowly operational amplifier, and the fact that fairly good analog instrumentation became available about 20 years ago. • Chemical insights by electroanalytical chemists. The use of aprotic solvents and the study of complicated organic systems, for example. • The development of more sophisticated theoretical underpinnings. Electroanalytical chemistry will develop in a number of promising areas in the coming years, according to Bard. Four categories can be identified: modified and molecularly designed electrodes, microelectrodes, electrochemical detectors (hyphenated techniques), and methods for in situ characterization of the electrodesolution interface. Modified and molecularly designed electrodes. This is a hot area already, with people preparing electrodes with polymer coatings and new types of organic conductors on the surface. By putting enzymes, or even cells or bacteria, on the surface of an electrode, researchers will be able to identify particular strains of bacteria or particular biological systems. Microelectrodes. Ralph Adams and Mark Wightman are currently working on the development of exceedingly small electrodes. These electrodes will be sensitive biological probes, able to, for instance, probe the behavior of single nerve cells or very specific areas of the brain. In addition, these electrodes will be of interest to the more theoretically minded electroanalytical chemist, since their small size will endow them with transport and current-level properties different from those of normal-size electrodes. Electrochemical detectors (hyphenated techniques). What's most important in electroanalytical chemistry today is not just elemental detection, but speciation—detecting the form of the element. Electrochemistry is a powerful technique for speciation, since the form of species determines where on the potential scale that molecule or ion is oxidized or reduced. By
ANALYTICAL CHEMISTRY, VOL. 53, NO. 6, MAY 1981 · 703 A
Focus face. Spectroelectrochemical, X-ray, piezoelectric, photoacoustic, and thermal techniques will be devised to probe this interface.
Henry Freiser organized and chaired the symposium combining electrochemistry with atomic absorption, mass spectrometry, or other forms of spectrometry, the speciation power of electroanalytical chemistry will be combined with the sensitivity and analytical power of the other techniques. Methods for in situ characterization of the electrode-solution inter-
Separation Science According to Calvin Giddings of the University of Utah, chromatography as a methodology is leveling off and forming a plateau. "On this plateau," added Giddings, "we can anticipate there will be many volcanic eruptions of certain techniques and special methods." Giddings predicts renewed interest and reemergence for some of the older techniques, such as electrophoresis and sedimentation. There is also promise for some newer techniques, such as field flow fractionation and hydrodynamic chromatography. But the most important trend to watch in separations is the development of separation systems optimization. In the separability domain, Guiochon has already derived equations that indicate the ultimate number of theoretical plates we can obtain with different chromatographic methods. In electrophoresis, for example, the maximum number of theoretical
plates is proportional to the voltage. In liquid chromatography, the maximum number is proportional to the system's pressure drop. By concentrating on these limiting factors, the number of theoretical plates in an analytical system can be maximized. A REPORT based on Giddings's presentation will appear in July. Spectroscopy Bonner Denton of the University of Arizona sees greater utilization of the notch filter mode in quadrupole mass spectrometry, and he expects major advances in the development of higher yield ion sources. Notch filters can, for instance, be used as high pass filters in LC/MS to eliminate low molecular weight solvent molecules when higher molecular weight components are to be determined. The direct reading spectrometer for optical emission is on the way out, said Denton: "It has high cost, it's big, it requires alignment to specific wavelengths, and, most important, it's only making very limited use of all the spectral data present in the system. What we really need is some kind of electronic readout." Today a number
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Focus horizontal axis. "I think the combination of an échelle spectrometer with the right type of solid-state camera device is going to make a dramatic impact on the future of analytical atomic spectrometry, and, of course, on molecular spectrometry as well," Denton predicted. The most important advantage of such an instrument would be its capacity to detect a large number of spectral lines simultaneously. A number of investigations involving systems of this type have already been reported, such as: ANALYTICAL C H E M I S T R Y , 1977,49,1112-1120;
Speakers at the symposium "New Directions in Analytical Chemistry" responding to questions from the audience. From left, Richard Van Duyne, Bonner Denton, Calvin Giddings, Bruce Kowalski, and Allen Bard of solid-state imaging devices, such as photodiode arrays, charge-coupled devices, and charge-injection devices, are being applied to the electronic processing of spectral information. Denton pointed out that to use such "xy" or "camera" devices, one needs to
have the spectral data formatted in two dimensions. One approach is to use an échelle spectrometer, which presents a spectrum as a two-dimensional pattern, with the grating orders observed in a vertical direction and the wavelengths varying across the
1978,50, 602-610; and 1980, 52, 916920; and Applied Spectroscopy, 1976, 30, 113-123. Denton predicted movement to techniques in which little or no sample preparation is necessary, or in which sample preparation is performed in an automated manner. One instance of this is the switch from the conventional Bernoulli principle small capillary nebulizer, which does not handle viscous samples well, to the Babington type of nebulizer, which can handle anything from motor oil to tomato sauce. Denton also saw continued progress in hyphenated techniques,
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Focus including gas and liquid chromatography with inductively coupled plasma detection. Chemometrics
Bruce Kowalski of the University of Washington makes a careful distinction between the concentration determined from a calibration curve and the truth. If you just want to do calibrations to determine concentrations, there's not much chemometrics can do for you, according to Kowalski. But if you're interested in the truth—how much of an analyte is really in the sample—then information science has lots to offer. "We're going to have a turn towards truth in analytical chemistry," Kowalski said. "We're not going to have the analytical chemist in his lab running a calibration curve, knowing full well that the water he's using to run his calibration has nothing to do with the real sample, and that he's got tremendous matrix effects." There are methods from information science, he explains, that will enable the chemist to find true concentrations, even in the presence of both matrix effects and interferences.
Referring to computerized instrumentation, Kowalski pointed out that today's instruments are still rather dumb. "They have big computers, and sometimes you're overbuying the computer you're getting (sorry if I said something unpopular). But the computers are doing rather simple things, in many cases just the things analog electronics used to do: simply collect data and print it out," he said. There's going to be more of a balance in the 1980s between the time it takes to separate out a mixture by instrumental chromatography and the mathematical resolution of signals. For example, in GC/MS, multivariate statistical methods can determine if two unresolved components are hiding together underneath one peak. And now there's a method to separate the components mathematically (ANAL. C H E M . , 1981,53, 518-522). "So why
put so much burden on the GC?" asked Kowalski. "Shorten the analysis and let the computer have the balance of the resolution." Surface Chemistry The solid/ultrahigh vacuum (solid/ UHV) interface continues to be the
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