INSTRUMENTATION BY RALPH H. MULLER
Specialized Analog Computer Resolves Overlapping Peaks
T ^ H E 152nd National Meeting of the American Chemical Society here in New York City has been an impressive event. As noted in the President's mes sage, 1971 papers were presented at 306 sessions by 3682 participating authors. No less impressive and interesting were the many exhibits of apparatus, instru ments, chemicals, and the innumerable tools used by the chemist, at the Expo sition in the New York Hilton. One exhibit attracted much attention not excluding ardent dial-twiddlers. This was the Dupont curve resolver. Many diverse analytical techniques, such as chromatography, electropho resis, and spectroscopy, produce curves which are sums of peaks or distribution functions. Often these peaks overlap and it becomes necessary to reduce the curve into its component parts to inter pret the results. The Dupont 310 curve resolver permits one to synthe size a complex curve exactly matching the observed curve. Each of its func tion-generator channels produces a peak shape corresponding to Gaussian, Lorentzian, or other distributions. In dividual peak parameters of height, width, and horizontal position are var ied independently until the resulting summation curve from all channels ex actly matches the original curve. I t is said that nontechnical personnel re quires less than 15 minutes instruction to master these manipulations. What happens after this is most interesting and useful. Each peak channel can now be presented separately on the oscilloscope or on an X-Y plotter for readout. The matching operations are illus trated in the schematic of Figure 1. The curve to be analyzed is placed on the copying desk of the 310 and its image is projected on the oscilloscope screen. A master curve of typical shape is synthesized on each channel and operating controls are used to inde pendently adjust the height, width, and horizontal position of each component peak. These peaks are electronically added by the 310 and the resultant -Circle No. 6 on Readers' Service Card
summation curve is superimposed on the original curve. In our opinion, a better way of explaining the schematic, and more conformity with the way it is drawn, is to say that the observer views two patterns simultaneously, the curve to be resolved and the synthetic curve. With good optics, the two images are in the same plane and no parallax errors occur. The screen of the oscilloscope is large (18 inches) with a black or white
image. Some other features include base line compensation to accommodate sloping or irregular base lines. The console is compact, requiring little space in the laboratory. All controls are within easy reach of the seated op erator. The instrument may contain up to 10 function generator channels, each with a diode matrix module for generating function shape, and an oper ating control module for independent MIRROR
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