edited by
computer m i e ~19.
Eastern Michigan universily.JOHN Ypsilanti. W.Mi MOORE 48 197
Bits and Pieces, 6 Most authors of Bits and Pieces will make available listings and/or machine-readable versions of their programs. Please read each description carefully to determine compatibility with your own computing environment before requesting materials from any of the authors. Guidelines for authors of Bits and Pieces appeared in the April 1980 issue of THIS JOIIRNAL. They are also available from the editor.
A Versatile and Inexpensive instrument/Computer Interface J. T. Burt. J. E. Byrd. G. L. Helm,
M. J. Perms. A. R. Ristow, and D. E. Wllkfnson Deparlmenls of Chemistry. Mathematics, and Electronics California State College. Stanislaus Turlock. CA 95380 In an effort to provide our students with an opportunity to use computer-interfaced instrumentation similar to that which is increasingly encountered hy them in employment situations, we have developed a particularly inexpensive and efficient computer interface system t.hat has been applied to a Finnigan Model 400 mass spectrometer and an Aminco stopped-flow spectrophotometer. The system is hased on an ISI-11 microcomputer (Digital Equipment Corporation), a locally designed and built interface, and the necessary software (-$600 for parts). When used with the mass spectrometer, the collection of a spectrum is initiated hy the user. T h e data is packed in the 4K memory and then passed via a serial link to a PDP 11/45 minicomputer where, using BASIC software, it is smoothed, the peaks located, the amplitudes measured, and the masses assigned.
Mass calibration is achieved by the comparison of the spectrum of a known compound (e.g.. CCld) to a file of assigned masses for the peaks in the calihration spectrum. T h e spectrum can then be displayed on a ~ e k t r o n f xgraphics terminal toaether with a list. of the 10 major peaks, their masses, and their normalized intensities ( s e e ~ i p1, . for an example). The scan range within the 400 mass units isvariahle using an adjustahle mass window and adjustable mass starting point. Reductions in window size allow mass regions ofpariicular interest to he analyzed with improved precision. Our tests show, however, that using the entire 0-400 amu range, the output is a t or near the resolution of the instrument itself. When used with the stopped-flow, the initiation of the chemical reaction hy the operator triggers the collection and storage of the transmittance values a t user-designated time intervals. The results are displayed on the monitor as a list of time and amplitude values whence they may he transferred to the timesharing system for subsequent analysis if warranted. Our BASIC program, STPPLT, assumes a first-order reaction, plots the kinetic data in the appropriate log form, determines the least squares parameters and calculates the half-life and rate constant (see Fig. 2). Repeated determinations yield a precision of less than f 2 % with none of the tedium normally associated with analysis of data collected by photographing an oscilloscope screen. The software for the collection and analysis of data includes four BASIC-Plus oroerams for the DEC PDP 11/45. MSCAN (350 s t a t e m e n t s ) : ~ ~(450 ~ ~ statements), ,~ STPFLO (200 statements). and STPP1.T (250 statements). These rewire IGK-16 hik'plus 8K virtual array, are block structuredand ~~~
The Cmputer Series auamptr l o delineate hcurrent Mate ol the art of comput er uosgs in chemical education while acMmmDdaling the needs and background of readers who have linis or no computer expenise. in aMitlon l o lull-length anicler, $hatdescriptions of specific applications of computers in classnxlms or
k e the prigramsdescribed. The editor's intention is that the Cornput% Series be understandable for beginners but at Me same time interestino for e x m r John W. Moore re&& jlir AB I r o n Franklinand Marshail College and his PhD from Nwthwertern Univerrihl, concentrating in physical inarganic chemishy. Following NSF-sponsaed p~sldoctaalW& at lhe
Environmental &view
Figure 1. FacSimile of t M Tektronix terminal soeclrum 01 1.2dibromoethane.
8&d.
Dr. Mwre has ~roducednumer&s
screen display of tM mas Volume 58 Number 7 July 1981
549
Figure 2. Facsimile of the STPPLT output on the Tektronix screen for kinetic by SCN-. date collected from the reduction of ~e(bipy)j+ lightly commented. The programs are user-oriented and carry out their functions automatically; however, for testing purposes and because of the possible requirement of minor modifications due to graphics display limitations, these proerams are easilv. senarated into their functional comnonents. . The necessary statements are included as remarks. Four additional programs, LOAD, MONBK, CHMON, and S T P are included. These are written in MACRO, require 4K-16 bits and are downloaded from the 11/45 automaticalls. Some are fully commented. All the programs and the interface should he transportable to other systems. We will make availahle detailed schematics, operating instructions, listings, sample output, and/or a listing on your tape (7 tracks, ASCII, odd parity, 800 BPI, unblocked) or floppy disk (for Tektronix 4921, ASCII, manual-tape mode). Send a blank tape or disk and a check for $10 made payable to Stanislaus State College Foundation, in care of Dr. Jim Byrd, Department of Chemistry, California State College, Stanislaus, Turlock, California 95380.
A Microcomputer-Controlled Gamma Scintillation Spectrometer Joseph W. Long
to analog-analog to digital converter provides communication between the comnuter and the external analoe world (Cromemco, Inc., 280 Bernardo Avenue, Mountain View, California 94040). Figure 8 shows how the computer and scintillation equipment are interfaced. The interface hardware hetween the computer and scintillation equipment consists of operational amplifiers that serve to match the voltage levels between the various parts of the soectrometer and the computer. After manual calibration of the pulse height analyzer and adjustment of the energy window width, the spectrometer may he operated completely under control of the microcomputer. The controllable parameters include upper and lower energy scan limits, scan speed, and direction. A scan may he interrupted, then continued, restarted from the heginning or aborted by single commands from the terminal. The chart recorder is controlled by the computer, which provides both the pen signal and chart-advance pulses. As a soectrum is run. it mas be outout to either the chart recorder; the terminal (as a high resolukion graphical display) or both. Once run, spectra may be saved on disk for reuse later. Latest versions of the ~ o r i z o nComputer allow storage of over 250 complete spectra on a single diskette (see Fig. 4). The software has been prepared in such a way that a student familiar with manual operation of the spectrometer requires perhaps ten minutes of instruction to operate it under computer control. This has been done by displaying on the terminal a "prompt line" that indicates the currently available operator commands a t all points within the program. Student response to this equipment has been enthusiastic and the system has proven useful in several ways: Students are intnldured to laboratory camputen, their interfacing and operation. 2) An inexpensive instrument of limited usefulness and rather poor reproducibility has been converted into a powerful, versatile, in a word-"intelligent"-spectrometer, comparable to commercial equipment costing many thousands of dollars. (This is not an in1)
Figure 3.
Spectrameter-mmputerinterlacing: black diagram. (IH = interface
hardware.)
Broome Community College Binghamton. NY 13902 This paper will describe a microcomputer-controlled scannina aamma scintillation soectrometer that has been construEteh in the Chemistry ~ e p a r t m e n at t Broome Community College. The spectrometer is in use by Chemical Technology and Medical Laboratory Technology students for whom it provides an example of microcomputer applications in chemical instrumentation. The spectrometer consists of "Nucleus" (The Nucleus, P. 0. Box R, Oak Ridge, Tennessee 37830) scintillation equipment interfaced to a Northstar Horizon I1 microcomputer. (Northstar Computers, 2547 Ninth Street, Berkeley, California 94710) The Nucleus equipment includes a NaI detector, nuke-heieht analvzer. and GM rate meter that toeether iuncrim d. a usahle, if primitiw. ganlma rpertronwter. T l w rwnputer inclucl(,sdual minillop))). disk d r i w and n videoterminal ([.ear S~egler,lnc., -14 North Rrookhur;t Street, Anaheim. C'aliiornia Wb0.1, to which hm heen added low-wsr. high rralurit~n.graphics hardware that emulstrs the Tektrmix 1010 gr;~phirstcwninal (Digital Knginrering. Inc.. 1775 'I'rihte Ihad, 5acrament0, California YShl51..An h-bit (liyital
550
Journal of Chemical Education
Figure 4. '%s spectrum replotted horn disk. Steps result hom use at an %bit analog to digital converter.
