The Developing Quality Control Laboratory Instrument Market T h e markets and market opportunities for analytical instruments are changing. It used to be t h a t the spectroscopist bought an infrared spectrometer to do everything the infrared analytical technique is capable of doing. Today the production manager of a citrus processing plant buys a black box with a meter t h a t reads in brix numbers. Inside the box is still an infrared spectrometer, but the plant manager really doesn't care—all he wants is an instrument t h a t is easy to use and t h a t will give reliable, repetitive, quantitative measurements of t h a t one specific characteristic. With increasing government regulations and growing demands for improved processing efficiencies, the total number of analyses required throughout industry has been climbing rapidly in recent years. Obviously this growth represents a golden opportunity for the instrument industry. To capitalize on it, however, the industry should understand the new requirements of the market and be prepared to modify and adapt its products to meet them. Presented as part of a seminar on "New Techniques in Analytical Instrumentation" sponsored by Robert S. First, Inc. in New York, October, 1979.
T h e expanding demand for analyses today is for repetitive quantitative measurements. And I emphasize the word "repetitive." Instrument manufacturers tend to shy away from directly specifying accuracies t h a t their instruments are capable of achieving. There is a good reason for this—quantitative analytical results are usually more dependent on the way the operator handles the sample—something beyond the manufacturer's control— t h a n on the instrument being used. With a skilled operator working in an ideal environment, most instruments will readily produce quite acceptable quantitative results, especially when several measurements are made on the same sample and the data averaged. But the new market for analytical instruments, as represented by the citrus processing plant manager, needs quick, reliable results from instruments operated by semi-skilled technicians, working in control laboratories which may be a room out in the plant or simply an out-of-the-way corner adjacent to the process itself— hardly the peaceful, controlled environment of the conventional analytical laboratory. Generally a particular instrument is dedicated to a specific measurement, being called upon to
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make t h a t measurement with a high degree of precision, frequently during a shift, often on an around-the-clock, day after day basis. This is what is m e a n t by repetitive quantitative analysis, and its special requirements may lead to quite different instruments t h a n those found in the general purpose analytical laboratory. Let us examine the specific requirements for control laboratory instruments and see how they affect this design. Control Laboratories Require D e d i c a t e d Instruments. Another key word—"dedicated"—represents one of the few special requirements t h a t definitely work in favor of the ins t r u m e n t manufacturer. A single purpose instrument obviously needs fewer controls than a multipurpose one. Often a radically simpler mechanism can be used as, for example, a simple filter to replace a variable monochromator in a dedicated infrared analyzer. Every parameter that can be made "factory set" rather than "field adjustable," not only lowers cost but improves reliability by eliminating setting errors and insuring functional reproducibility. Building instruments with a minim u m of exposed controls may repre0003-2700/80/0351-222A$01.00/0 © 1980 American Chemical Society
Report Paul A. Wilks, Jr. General Analysis Corp. P.O. Box 2466 Darien, Conn. 06820
sent a significant change in design philosophy on the part of the instrument manufacturer, however. He has probably been accustomed to building all kinds of versatility into his research or analytical laboratory models. Dedicated instruments require a whole new approach to instrument design. In eliminating "field adjustment versatility," however, the manufacturer must be careful to retain "factory adjustment versatility" which makes it possible to switch a basic instrum e n t from one dedicated application to another at the manufacturing level. Control Laboratories Inevitably Have Harsh Environments. It seems to me t h a t whenever I enter the confines of a control laboratory, I immediately begin to perspire profusely from the high temperature and 100% plus humidity while my teeth chatter because of the vibration transmitted through my thick soles and I converse with difficulty with the supervisor because of the noise and hustle and bustle around me. T h a t an instrument can be designed to operate under these conditions, reliably, over long periods of time has always seemed like a miracle to me. Making an instrument insensitive to wide fluctuations in ambient temperature is probably the most difficult design problem t h a t the instrument manufacturer must cope with. Yet such temperature insensitivity is essential if long-term repetitive analytical precision is to be achieved. High humidity and vibration are generally much easier to handle through sealing, purging and damping techniques. In any event, environmental considerations are far more significant for control laboratory instruments than for instruments destined for research laboratories. Minimum Sample Manipulation Leads to Maximum Analytical P r e cision. By far the greatest source of error in repetitive quantitative analysis comes from the sampling handling process. Each step a sample must be put through before analysis, i.e., dilution, filtration, separation, etc., adds one additional opportunity for operator- or instrument-induced error. Ideally, the sample should be analyzed
continuously in the process stream itself. T h e next best approach is to extract a sample from the stream, take it to the instrument and, without further treatment, place it on the sample stage or inject it onto the column. There are some classes of samples which, because of nonuniform composition, require a mixing or homogenizing step. Meat is a good example. T h e analytical method used also has a bearing on sample handling simplicity. Optical—especially spectrometry—techniques are generally more conducive to high repetitive analytical precision than separation (chromatographic) techniques. Sample size is usually not critical, as it is with chromatography, and with at least one optical method, infrared spectroscopy, the sample can almost always be examined in the process stream, leading to greater precision through sampling simplicity. In fact, where it has enough sensitivity to make the particular analysis, the modern quantitative infrared analyzer equipped with an internal reflection sampling system and a microprocessor best meets the overall requirements of control laboratory analysis. The Higher the Signal-to-Noise Ratio, the Better the Reproducibility. Every instrument has a background noise level. T h e closer the signal t h a t is being measured gets to t h a t level, the more difficult it is to distinguish t h a t signal from noise and the poorer the reproducibility of the quantitative measurement. T h e instrument designer is always faced with design trade-offs—he can improve one
performance characteristic at the expense of one or more others. When designing a quantitative control laboratory-type instrument, the designer's object should be to maximize energy throughout (signal). In the case of a spectrophotometer this is accomplished by opening t h e slits at the expense of resolution. Not only do high signal levels increase measurement precision, they also permit faster response times and hence reduce time per analysis—both enabling the instrument to handle more samples, and allowing less time for sample degradation. Many samples have a disconcerting way of changing composition with time, thus the more quickly they are analyzed, the better. Dedicated Instruments Can Read D i r e c t l y in Composition Units. One of the simplest steps t h a t the instrum e n t manufacturer can take, yet the one which undoubtedly has the greatest sales appeal as far as the customer is concerned, is to make the dedicated instrument read directly in the composition units the customer uses: percent, ppm, brix number, mg/L, etc. Even where the instrument outp u t is nonlinear, simple microprocessors can a d a p t the output to a linear meter scale or, better yet, to a digital display. Outputs should be made computer compatible. Direct composition readouts eliminate another source of quantitative error—the one which occurs when an instrument reading must be taken to a calibration chart in order to correct it to composition. By now it should be clear t h a t in-
Paul A. Wilks, Jr. has been associated with the analytical instrument field, particularly in the areas of infrared spectroscopy and gas chromatography, since graduating from Harvard in 1944. He was the founder of Wilks Scientific Corp., now a part of the Foxboro Co. Mr. Wilks is now a consultant in infrared instrumentation and analytical instrument marketing. He recently founded the General Analysis Corp., which will provide analytical services throughout the U.S. ANALYTICAL CHEMISTRY, VOL. 52, NO. 2, FEBRUARY 1980 · 223 A
A handful of good reasons why you should monitor HPLC at 206 nm
Heart of LKB's new Uvicord0* S UV-monitor is an RF-excited gas discharge lamp with an intensity at 206 nm that is orders of magnitude higher than any deuterium lamp. High photon flux reduces noise, typically to
