REPORT FOR ANALYTICAL
CHEMISTS
Application of Computers to the W o r k of the Analyst Electronic computers are being widely used to perform repetitive calculations in routine analytical testing. A symposium sponsored b y the Division of Petroleum Chemistry at the September 1957 meeting of the American Chemical Society included several papers of interest to analysts in the field. This article presents some of the highlights of these papers and surveys some aspects of analytical laboratory data processing by machine methods. Three of the symposium papers dealt with topics related to use of computers in mass spectrometry, which is the chief application of electronic computers in analytical work. The use of a computer to calculate emission spectrog r a p h s results gives another example of a routine, repetitive calculation suited to the computer. The operation and management of a service laboratory involve much data processing. This is a field in which the computer can help management do a better job at a lower cost. The high cost of such equipment requires a large volume of computer w o r k to justify the expense.
applications of computers THtoE tchief h e work of t h e analyst are in
E. A . M c C R A C K E N is h e a d of t h e A p p l i e d M a t h e m a t i c s G r o u p of Esso Research Laboratories, Esso S t a n d a r d O i l C o . , in Baton Rouge. H e joined Esso Research Laboratories in July 1944, and worked in t h e f i e l d of petrochemical research f o r several years. H e b e g a n f u l l - t i m e work in statistics and a p p l i e d mathematics in 1955 a f t e r an assignment in d a t a correlation and i n t e r p r e t a t i o n . H e received an A . B . f r o m Earlham C o l l e g e , Richmond, Ind., in 1938 a n d an M . S . in organic chemistry in 1944 f r o m Purdue University. H e is a m e m b e r of the Baton Rouge Section of A m e r ican C h e m i c a l Society.
making tedious, repetitive calculations. T h e main incentive for using t h e computer on these jobs is t h e labor saving t h a t results. Calculation of mass spectrometer analyses is t h e outstanding example of this application, a n d computers have been widely used for this purpose for several years. A large reduction in cost p e r sample for mass spectrometer analyses was made b y the change to electronic computer calculation. N o doubt a number of similar instances in analytical work have not been reported in t h e literature. F o u r papers dealing with applications of computers of interest t o analysts were reported a t a symposium sponsored b y t h e Division of Petroleum Chemistry a t t h e N e w York A M E R I C A N C H E M I C A L SOCIETY meeting
in September 1957. These papers are being published as a group in this
issue
of ANALYTICAL
CHEMISTRY
{2,
4—6). Three of these papers report new contributions in t h e field of use of computers in mass spectrometer analyses: (1) transmission of mass spectrometer results from remote locations to a computer for calculations, (2) setting u p of calibration matrices with t h e computer, a n d (3) improved methods of solution t o gain precision. T h e fourth paper describes calculation of routine emission spectrograph r e sults using a medium speed computer. Another area in which computers are being used is in analytical laboratory management. A system described by Addison, Spencer, a n d Charlet (1) uses punched cards to keep track of the analytical load, and a computer is not an essential p a r t of t h e system. However, if one is available, it m a y be used t o prepare reports based on the punched cards which are valuable aids to management.
VOL. 30, NO. 5, MAY 1958 ·
19 A
REPORT Application to Mass Spectrometer Analyses
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· ANALYTICAL CHEMISTRY
Systems along the line described by Dudenbostel and Priestley (S) are widely used. This paper described the calculation of results with a relatively slow speed computer, using the punched card output of an automatic digitizer on the mass spectrometer. The savings in manpower and consequent reduction in cost over previously used systems were large (Table I ) . The original methods of calculating compositions from mass spectrometer results used an electrical analog computer or desk calculator, and obtained peak heights by measuring photographic records. Use of an electronic computer plus automatic digitizers reduced manpower requirements by 80%. Faster computers than the card-programmed calculator described in Table I are generally used today, which reduces the cost below that shown.
Assembly of Mass Spectrometer Calibration Matrices
Before the composition of a sample can be calculated from mass spectrometer results, a suitable calibration matrix must be available. Results on pure compounds are the basis for the calibration. Setting up calibration matrices is not much of a problem, if routine analysis of plant streams of simple composition is involved. This is usually not the case in research work. New sample types occur frequently and the number of components is usually relatively large. Hence, ^ the setting up of the calibration matrix is a substantial part of the cost of running samples of this type. The computer program described by McAdams (5) takes calibration data in punched cards from the mass spectrometer digitizer and does a number of things: (1) corrects for instrument sensitivity, (2) corrects for size of sample, (3) corrects for background spectra, (4) corrects for known impurities in the calibrant, (5) averages spectra where necessary, and (6) assembles and forms a square matrix. This square matrix is now ready for inversion, which is carried out by conventional techniques as a part of the matrix preparation program. The reported reduction in manpower in preparing moderately large calibration matrices is notable. For example, the time to prepare a matrix for handling 20 components was reduced from 25 to 1.4 man-hours. Computer time (for a medium-speed computer) was increased by 12 minutes by doing the assembly job on the computer.
REPORT FOR ANALYTICAL CHEMISTS
Table I.
Time Requirements for Measuring and Calculating Mass Spectrometer Data
7faJwkw/7CG0U!éïâ?*W
(Man-hours required to run thirty 20-component gas samples) Photographic Record Analog Computer Instrument* Chart measurement Calculation Total, man-hours Man-hours/sample
10 10 30 50
1.65
Photographic Record 602A (IBM)" 10 10 7.5
27.5 0.92
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Sadie6-" CPC (IBM) 8 0 3 11
0.37
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Inversion of M.S. Calibration Matrix
Calibration information is converted to an inverse matrix for calculation of actual results on unknown samples. This mathematical process of inversion can be done in several ways. In using the conventional inverse negative amounts of some components are fre quently indicated by the analysis. Since these have no physical meaning, they are usually reported as zero. Setting a negative value to zero after calculation of the sample analysis is completed does not, of course, correct for equivalent errors which are present in other components. These errors are small and are customarily ignored. Using a triangular inverse as de scribed by Hopp and Wertzler (4) gives an opportunity to avoid the effect of negative components. Com ponents are calculated in carefully selected sequence in the computer pro gram and any negative value is set to zero before proceeding to the next component. Thus, the effect of the error is not carried through to com ponents calculated in later steps. The effect of small random errors in peak heights on the errors of final values for some components is mark edly reduced. This is illustrated by comparing results using the triangular inverse with those using a conventional square inverse. Transmission of Mass Spectrometer Data
It is a general rule that the larger the electronic computer the cheaper the cost of calculation per problem. How ever, a large volume of useful computer work must be found to justify the cost of even a medium-sized magnetic drum computer. For example, the cost of an IBM computer is in excess of $200,000 and leasing in excess of $3750 per
month. An answer to this situation is the use of a transmission system to connect mass spectrometers in remote locations to a central facility, as de scribed by Mihm, Pollock, and Shelton (β). This system has been success fully servicing a plant 350 miles from the computer. In this system punched cards from an automatic digitizer at the mass spectrometer are fed to an IBM trans ceiver. The information in the punched cards is sent by teletype line to the computer center, where an identi cal set of punched cards is generated. Calculated results from the computer are sent back to the plant by the same route. The estimated rental charges of the computer, its auxiliary equipment, and the transmission equipment is about $1 per sample. Also calculated at the center for plants in remote locations are material balances, yields, and process informa tion. These calculations require other load information in addition to one or more mass spectrometer analyses. Consolidation of calculation of analyti cal results with calculation of work ups for commercial and pilot units re duces transcription of data from one record to another form. Data handling is thereby made more efficient.
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Calculation of Emission Spectrographic Data
Use of a computer to calculate re sults from emission spectrographic data is described by Anderson and Moser (2). This is another instance of use of a computer to take over a tedious routine job with a consequent manpower saving. This particular computer program also furnishes an estimate of error for the guidance of the user of the analytical results. In a routine analysis using the com-
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REPORT FOR ANALYTICAL CHEMISTS
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puter system the starting information loaded to the computer program is the spectrograph^ film line transmittance for the element plus that of the inter nal standard. The relative intensity ratio is computed and used with the calibration information to calculate concentration. The calibration coeffi cients are calculated from data at known concentrations by a special com puter program. A polynomial equa tion is fitted to the intensity versus con centration data by a multiple regres sion technique. An estimate of experi mental error is derived from the resid ual error of this fitting and reported with each analysis. This error esti mate depends on conditions at the time of calibration. It will not be as useful in data interpretation as an error estimate based on analyzing a standard sample on a "blind" basis over a period of time. It does, how ever, give the user of the data some idea of precision of the analytical method. Analytical Laboratory Management
The supervisors of the routine ana lytical laboratories of any sizable chemical company, petroleum refinery, or research organization have a large problem in data handling, record keep ing, and work scheduling. A com puter center with its auxiliary equip ment can be of real help on this prob lem. Addison, Spencer, and Charlet (1) describe a punched card system for an analytical laboratory. This system is of interest in relation to the use of computers in analytical work. A set of punched cards is prepared for each sample submitted for analysis. Mark sense cards for each test go to the laboratory supervisors. Groups of cards are selected and turned over to the analyst for running of the tests. In this way the supervisor schedules the work of each analyst. In many cases the test result is mark sensed directly on the card with no other record being made by the analyst. At the time the set of cards is made for the analyst, another set is made and put in an inventory file. These are matched out of the file in a colla tor operation when the completed card is returned by the analyst. The in ventory file is used to make daily printed reports on the tabulator show ing the backlog on each test and the delay times on the samples. The completed cards are used to prepare report sheets on the tabulator which are returned to the person re questing the analysis. Thus, trans cription of results by clerks and ana lysts is essentially eliminated.
A number of very useful reports are readily prepared daily, weekly, or monthly, using the punched cards as a basis. Some of these require a com puter for convenient preparation. These reports are used for the following purposes : 1. The size of the backlog for the various tests indicates points needing attention. Reassignment of manpower or decrease in sample input may be required. 2. The record on service time shows whether proper scheduling is being done. 3. Output figures give a direct meas ure of efficiency for the laboratory groups and for individual analysis. 4. Output figures also show the amount of analytical work being done for each research project or producing unit. 5. Time charges to various jobs can be made from the output record or prepared as an additional report by the computer. The system has shown a number of advantages: (1) It makes for more effective laboratory management, (2) reduces manpower assigned to data reporting, (3) increases speed and ac curacy, and (4) makes records more accessible. Conclusion
This discussion has attempted to survey areas in which computers are now being used by the analyst. The major application is in repetitive routine calculations. Automatic data processing has a place in the operation of service laboratories, particularly where the volume of useful computer work is large enough to justify the cost of a computer. In this connec tion it is possible to connect mass spectrometers in remote locations to a central facility. Literature Cited
(1) Addison, L. M., Spencer, Ε. Η., Charlet. Ε. Μ., ANAL. CHEM. 50, 885
(1958). (2) Anderson, F. Vv"., Moser, J. H., Ibid., 50, 879 (1958). (3) Dudenbostel, B. F., Jr., Priestley, W., Jr., Ibid., 26, 1275-8 (1954). (4) Hopp, H. F., Wertzler, R., Ibid., 50, 877 (1958). (5) McAdams, D. R,, Ibid., 50, 881 (1958). (6) Mihm, C. H., Pollock, L. W., Shelton, R. O., Ibid., 50, 874 (1958). VOL. 30, NO. 5, MAY 1958 ·
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