INSTRUMENTATION by Ralph H. Müller
N e w electronic spectroanalysis system promises to speed analyses
Figure I . Engineers Ronald Taplin and Mortimer Rogoff examine punched paper tape that reports absorbance of infrared. FTL's electronic spectroanalyzer consists of spectrophotometer, control console, and d i g i t a l computer
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3) £
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Figure 2 . Five-constituent spectrogram of a steroid mixture. Heavy vertical lines are wave-length markers, not sampling points
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MIC/K/N3
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//
Steroid Analysis of Five-Constituent Mixture Actual Mixture Concn., M g . / Constituent Gram CH 2 C1 2 Androsterone 1.47 11-Ketoetiocholanolone 0.52 Etiocholanolone 0.91 17-a-Hydroxypregnanolone 0.23 11-Hydroxyetiocholanolone 0.27 MOTC*
CAM-»
Result of Kleotronic Spectroanalysis 1.445 0.512 0.960 0.218 0.31
OΝΕ can expect to see computers used more and more, as our analyti cal instruments become more highly developed. There are two factors which make t h e use of computers advisable. I n large laboratories where m a n y re petitive analyses a r e performed, many of t h e m automatically recorded, t h e computer is a logical and economically justified item. I n t h e plant, where dozens of process variables a r e re corded, one no longer sees the m a n with the d a t a board copying down meter readings. T h e Honeywell computer system, which we described some time ago, interrogates these instruments, compares t h e m with t h e desired set tings, collates them, and types the val ues or punches them on tape for further processing. Warning signals a r e also provided for instantaneous indication of process upsets. I n such systems, the . "'loop" is easily closed so t h a t the com puter can "order" corrective measures. These elaborate installations a r e war ranted on t h e basis of economic con siderations. From the scientific standpoint, elabo rate instrumentation can provide us with more precise and detailed informa tion. More often than not, it turns out t h a t information becomes available a t such a prodigious rate t h a t a few hours of measurement m a y require weeks of calculation in order t o assimilate and interpret the data. This is precisely the point a t which the computer is required. I n pure science, this is also the time t o forget about t h e whole thing. More t h a n likely, t h e research budget has been used u p in purchasing the record ing instruments. On large, heavily en dowed projects, such investments m a y
Figure 4 . Digital sampling o f total fingerprint spectra
SAMPLE
CONTROL -TRANSFORMERSBRUSH SELECTION LP SIC
« ONLY THESE POINTS USED IN GRAPHICAL ANALYSIS
14 BIT 1 TRANSLATING MATRIX STORAGE
^PAPER TAPE PUNCH ••
•
"
FTL ANQ1C0NCONVERTER
BACKGROUND ERROR IS SUBTRACTED TO GIVE TRUE SPECTRUM
I
-DIGITAL SAMPLING POINTS
PUNCHED A VALUES IN—^ BINARY CODED DECIMAL DIGITS
Figure 3. converter
A n a l o g transmittance t o d i g i t a l absorbance
INFRARED WAVE LENGTH DIGITAL SAMPLES CODE PUNCHED ON TAPE
VOL.30,NO.5,MAY1958·
65 A
INSTRUMENTATION
instrument abstracts
Cary
Applied Physics Corp./362 W. Colorado
Street/Pasadena/California
at the Richfield Laboratories
Cary Model 14 Spectrophotometer enables determination of lead concentrations to one part per billion
The destructive effect of lead on the activity of costly catalysts makes accu rate determinations of even minute amounts extremely important. With improved techniques now in use at the new Research Laboratories of the Rich field Oil Corporation, Anaheim, Cali fornia, chemists can determine lead concentrations in naptha charge stocks within one part per billion. The conventional dithizone colorimetric procedures can be used to esti mate the lead concentration to an accuracy of approximately 10 parts per billion. A refinement of this procedure, employing the Cary Model 14 Recording Spectrophotometer, is used to more pre cisely determine the concentration. The color intensity of the lead dithi zone solution is measured at 5100 Ang stroms for the unknown sample and for two standard solutions whose concentra tions are respectively a little more and a
little less than the estimated concentra tion of the unknown. By interpolating, the analyst can then determine the lead concentration of the unknown to an accuracy of one part per billion or better. In this procedure, the high photomet ric accuracy of the Model 14 is of pri mary importance in reliably recording the minute differences in absorbance values between the sample and stand ards. This high photometric accuracy is one of several performance features pro vided in each Cary Recording Spectro photometer to a degree not found in any other similar instruments. Perhaps these advantages can lead to new break throughs in your analytical techniques. Complete information on both Cary Spectrophotometers, Model 11 and Model 14, is contained in a bulletin which is available upon request. Ask for Data File AlO-58.
BRIEF SPECIFICATIONS OF CARV SPECTROPHOTOMETERS MODEL 14 MODEL 11 RANGE
2100A to 8000X
1860Â to 2.6 microns.
STRAY LIGHT
Less than 0.0001% over most of working range.
Less than 0.0001% between 2100A and 1.8 microns; less than 0 . 1 % at 1860Â and 2.6 microns.
SCANNING SPEEDS
From l.oS/sec. to 1258/sec.
From 0.5Â7sec to 50oS/sec.
RESOLUTION
Better than Ι.οΧ throughout range.
Better than l.oS U.V.-visible region and 3.0Â" near-infrared.
WAVELENGTH ACCURACY
Better than 5.0Â U.V. region and 10.0Â visible region.
Better than 4.0Â throughout range.
REPRODUCIBILITY
Better than 0.5Â U.V. region and 3.oS visible region.
0.5Â throughout range.
PHOTOMETRIC REPRODUCIBILITY
0.004 in absorbance.
0.002 in absorbance.
For further information, circle number 66 A on Readers' Service Card, page 85 A
66 A
· ANALYTICAL CHEMISTRY
be feasible and the rapid accumulation of precise information then becomes possible. An elegant example has been brought to our attention. A new analyzer, combining infrared spectroscopy and electronic data processing equipment, has been developed for the Sloan-Kettering Institute for Cancer Research by the laboratories of the International Telephone and Telegraph Corp., 67 Broad St., New York 4, New York. [The editors of ANALYTICAL CHEMISTRY are
not
in a position to describe this equipment nor answer questions about it, other than what is written here and elsewhere in this issue. Also, as we understand it, the equipment is not for sale, at present.] The Sloan-Kettering scientists, who participated in the early stages of development, had in mind a means of rapid interpretation and identification of polycomponent mixtures of hormones as given by infrared spectrophotometry. The system consists of a recording infrared spectrophotometer, a recording device which encodes the data in numerical form on paper or magnetic tape, a "library" containing on tape the infrared absorptions of possible constituents, and a high speed electronic computer to perform the mathematical calculations necessary for a quantitative analysis of the sample. The complete installation is shown in Figure 1. According to Ronald Taplin and Mortimer Rogoff, the sequence of operations may be described as follows: In the polycomponent system one seeks values for the absorbances of the various constituents at several wave lengths. In this system the spectrum is broken into 3000 wave length samples and the infrared absorbance at these points is stored on punched tape. In gathering the specific absorbances at these wave lengths for each of the constituents and with the appropriate coefficients, the solution of the large number of simultaneous equations is then performed by the computer. In Figure 4, the digital sampling points are shown as well as the background error, which is automatically subtracted. The recording spectrophotometer is constantly providing a shaft rotation which is an indication of absorbance. This information is encoded as shown in the schematic of Figure 3, wherein transmittance values are converted with a logarithmic cam to absorbance values and then converted to binary coded values which are punched on tape. Figure 2 is an analysis of a five component steroid mixture. For the limited portion of the spectrum used, 390 individual points in the spectrum
INSTRUMENTATION
Peristaltic-action
PUMPS Pump Liquids Peristaltically Through Rubber or Plastic Tubing ROTATION MOVEMENT
TUBING
Small
Pump
(shown above)
pumps at a rate of .2 ml. per hour to 15 ml. per minute, adjustable during operation. Device can be used for: administration of sterile fluids to animals; perfusion of body organs; micrometering, etc. Cat. No. 5-8950, furnished with initial supply of plastic tubing $159
Large Pump (at right)
\
pumps at a rate of 25 to 600 ml. t per minute, adjustable during operation. Used for transferring or / circulating corrosive fluids; trans- * fer of pathogens between contain-" ers; circulation of fluids in cooling systems, etc. Cat. No. 5-8952, furnished with initial supply of plastic tubing $385
Full
information
contained in
Bulletin 2 2 8 8 - H furnished upon request
AMINCO AMERICAN INSTRUMENT COMPANY, INC. SILVER SPRING, MD., IN METROPOLITAN W A S H I N G T O N , D. C . For further information, circle number 68 A on Readers' Service Card, page 85 A
68 A
· ANALYTICAL CHEMISTRY
were measured and collated. Some peculiar advantages of this system may be mentioned. The computing system is automatic and does not require complex programming routines for each problem. Compactness is possible because the instrument is completely transistorized and maintenance is simplified by the use of printed circuit elements. The new system makes it possible to obtain an accurate monitoring of instrumental errors. A check computation is made before each analysis, and the spectral response of a standard chemical compound is matched by the computer with a similar spectrum recorded when the instrument was initially aligned. Interpretation of any deviation from this match provides a very sensitive indication of the cause and extent of instrument malfunction. The development engineers believe that further application of these error reduction techniques offers the interesting possibility of making infrared spectra recordings interchangeable between different instruments. This would assist greatly in the interchange of precise data between laboratories. Some variations in this technique are also possible. For example, a synthetic spectrum can be constructed from the digital library in accordance with the amounts of constituents obtained from a given analysis. By subtracting the synthetic "answer" spectrum from the original "unknown" mixture spectrum, an error function is obtained. Examination of this function will show the portions of the spectrum which obscure the results due to optical nonlinearities in the chemical mixture. Serious deviations will indicate a recomputation of the problem leaving out these wave length regions subject to error. The error function will also disclose the presence of any unsuspected component in the original analysis. Another method is used for repetitive quantitative analysis of known mixtures. This is a common requirement in an analytical laboratory. For this application a set of spectral biorthogonal functions is previously computed for a given mixture. The biorthogonal function has a numerical value assigned to each wave length sample. When each biorthogonal sample value is multiplied by the corresponding sample value in the unknown mixture, all constituent concentrations except the one assigned to this biorthogonal function are reduced to zero. The remaining value after summation of all samples is the precise amount of the wanted element present in the mixture. This method will provide an analysis in an elapsed time of 30 seconds for each element.
