Fsg~re2 The ntrarm spectr.m of 2 Gd-sec.3.1) pnmo from 5000 to 1000 cm 'snow np m e par toon ot a non-n,drogen uondeo Oh qro.p a 3640 cm-': Apple ii graphics
a numher of other useful features. Labels can he added later using the shape tables described ahove. Figure 2 shows a photo of an infrared spectrum made as descrihed. The main peaks are labelled in cm-l. Granhics in general take more time to develon than most micrucompute~applications,hut over a period time as the lihrarv of materials builds un and. if devices like the aranhirs tablet"speed up the development; the impact of graphics apnlications on microcomnuters should sumass many of their other applications. The followine two disks are available and require a 48K Apple I1 with Krmware Applesoft and one disk drive. Disk "AB-curves" contains 11acid-base titration curves,the 3 mode display program as descrihed ahove, and the titration curve generating program for generating new curves. Disk "IRspectra" contains 11IR spectra illustrating how most of the basic functional groups appear along with a 2 mode display program (no auto alternation). These disks are availahle for $25 each which includes the cost of the disk and postage. Send check payable to G. L. Breneman with order.
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simulation Clarence H. Suelter, Allan J. Morrls, and Don Hlll Department of Biochemistry Michigan State University East Lansing, MI 48824 Scintillation spectrometry is an important technique with application in a wide variety of research disciplines. Modern sophisticated instrumentation is available that requires little training for use by the experimentalist. In fact, it might he argued that the design of modern instruments tends to cover up the many subtleties involved in the correct application and analysis of the dataohtained with this technology. Thus, the experimentalist who has a theoretical background in scintillation spectrometry and experience in the analysis of data ohtained with a scintillation spectrometer will be able to use the technology in a more effective and innovative way than those not so trained. Therefore, a computer program was written to simulate a scintillation spectrometer in order to Drovidea potential user (student)with a realisticexampleof the process required to use the instrumentation to count carbon-14 and tritium or a mixture of these isotopes. Droeram was desiened to simulate a dual channel The . " scintillation spectrometer with a log gain amplifier and external standard ratio device (Fie. 3). I t allows students to collect simulated data whose 'an&& provides the kind of experience needed to use scintillation spectrometry confi-
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988
Journal of Chemical Education
Figure 3. Photograph 01 CRT display after completion of count of a tritium standard in channel A with windows, count limit, and time limit set as indicated. The counts observed in channel Bare due lo background.
dently in the research laboratory. Completion of this simulation assumes a background in the theory of radiation decay, scintillation spectrometry, and statistics of counting. The student is asked first to determine an energyspectrum for both tritium and carbon-14, in order that the proper window (discriminator) settines for each channel can he ascertained. After setting the windows for each channel the student then determines the effect of a auencher. methvl nitrite, on the count rate of both the "C and 3H stahdard; and finallv the comnosition of an unknown mixture of I4C and 3H. The student initiates the program and proceeds by varying the windows for each channel over narrow ranges. After proceeding through the effective energy profile of both 3H and 14C,the student plots the observed counts in each channel for both '4C and 3H as afunction of the average window settings to obtain the energy spectrum of each isotope. The student uses these spectra to select the proper window settings for each channel in order to minimize I4Ccounh in the 3H channel and to exclude 3H counh from the 14Cchannel. After selecting the proper window settings, the student counts a series of 3H and '4C standards with increasing amounts of quencher, methyl nitrite. Sufficient auencher should be added so that the external standards ratio goes as low as 0.25. Both the count rate in each channel and the external standards ratio are recorded for each level of a quencher added. The standard deviation of the counts is nroved on the cathode rav tube (CRT) of the microcomput& to indicate the importance of counting for sufficient time to obtain a reasonable standard error. All count rates are programmed to include a small random error. After determininn the effect of auenchers on the count rate of thrstandards, the student cou& an unknown mixture of 'Hand "C. Using the external standard ratio obtained with the unkllown and the plot of counting efficiency for 3H and '4C versus the external standards ratio, obtained from the study of the quencher on the3H and "C standards, and a plot of the spill of IT counts in the W channel u,ith increasing amounts of quencher, the student has sufficient information to calculate the composition of the unknown as disintegrations of 3H and 14C ner minute. Since the unknown mixture is generated by the microcomputer via a random number generator. a different unknown is obtained each time the exercise is completed. Acode for the composition of the unknown appears on the CRT display after the unknown mixture is counted. The cluefor its decipher is available for the instructor's use. Completion of this exercise provides a realistic experience in the use of a scintillation spectromerer. The microcomputer replaces the expensive scintillation spectrometer in the teaching ofdara collection and analyses. In addition it allows
one to teach the intricacies of data collection and analysis without, a t the same time, challenging the student with the proper use and handling of radioisotopes. The theory for various aspects of scintillation spectrometry must he provided via another mode. The program entitled SIMULSCINT was written for a Commodore P E T microcomouter with 16 K RAM. It is availahle m a c3ssette rape f0;$40 frmn the Markrung Divison. Instructional Media Center, Michigan Srnte I'niversitv. .. ~ a sLansing, t MI 48824.
Simulation of Chemical and Enzyme Kinetics Experiments Clarence H. Suener and Don Hill Department of Biochemistry Michigan State University East Lansing, MI 48824 Computer programs for a microcomputer have been written to simulate a variety of laboratory techniques and methodologies. They are intended to be used to familiarize a student with the orohlems and orocesses involved in the anolication of a partiklar techniqie in the laboratory. They &e not intended to replace an actual laboratory experiment. Completion of the simulation provides the student with simulated data that can be analvzed hv accepted procedures. The aim is to reduce the time iequirid f o r a student to design, complete, and understand an experiment. I'rogrnm KINZYMI.:. The successful assay of nn enzvme and the determination of its kinetic parameters, the hlirhac.lis constant (K,,) and the maximum vebcity (\',:,,I, arr l~nsir rxperiences of all stl~dentsin hiorhemistry. In fact, it is reasonahle toargue that all profussional biuchrnlisu, no matter what t heir specific arm of interest, will hnve a need to wdrk with enzvmes a t some time in their careers. One of the iratures oienzymc ratalgsii that students uften have difficultv" in -erasoine is the extraordinnrv eifirimcv of the catalytic process. ' s t d e n t s will often conclude afte; an enzvme exoeriment that thev have an inactive enzvme menaration, when, in fact, the reaction was complete &fore they made their first observation. Another auestion often asked is ..what subsrratr
