include feedback or allosteric regulation. This is a desirable feature because it permits the student user the opportunity to alter those concentrations andlor enzyme activities in a way consistent with feedback or allosteric regulation. Although, GARFKEL is written in FORTRAN VERSION 5 for use on the CDC CYBER 172, i t should he compatible with any FORTRAN 5 or FORTRAN 4 complier. Minor modifiraticmx in statement and inpur-output formnttin$ may he required to run CAllFKEL on other systems. The nroaram uses douhlr urecision and reauires 75K hvtes 172. he (60 Gitsiyte) of memory u;hen run on the ~ Y B E R arravs are for data storaee " onlv and not used for data oroceasing. 'l'ht. initial metaholite concentrations and rate constantsare thosedesrribed by Carfinkel and Hesj 151. For the second set of computed data, where changes are made in concentrations and/or rate constants, values are usually changed by a factor of 100. However, the program can be modified and these values as well as the initial values can he changed by any factor desired. A source listing of GARFKEL is available from Lawrence J. Tirri, Department of Chemistry, University of Nevada, Las Vegas, Las Vegas, Nevada 89154. Write for additional information regarding the availability of this program on magnetic tape or floppy disks. Acknowledarnent -
The authors are grateful to the University of Nevada System Computin~Center and tu Sally A. Jarmow, user liaison, for their Galuable support and assistance in the development and operation of this program.
Interfacing an EM-360 NMR with an Apple lle Computer James C. Swailz and John T. Creed Thomas More College Crestview Hills, KY 41017 We have interfaced an Apple IIe microcomputer with our Varian EM-360 NMR spectrophotometer. This system, which was assembled as a senior research project, permits us to demonstrate data collection, signal averaging, data storage and retrieval, data analysis, and data manipulation. Similar interfaced systems have been reported 6 9 ) ;however, the one described here is significantly simpler with respect to the required hardware and software. The hardware consisted of an Apple IIe microcomputer with one disk drive, an ADALAB interface card1, a difference amplifier, an inverting amplifier, an X-Y plotter or Y-T Recorder, and a Varian EM-360 NMR spectrophotometer. The Varian EM-360 NMR is a relativelv simnle instrument to understand with respect to the mechanisms for scannine and recordine of spectra. The maenetic field sweep. by a potekometer that for the EM-360, is connected directlv to the X-axis of the NMR recorder, thus as the pen is moved across the X-axis by astepper motor, the magnetic field is automatically chanced. It require3 1000 p&es from the sweep time circuit t o t h e stepper motor to cover the entire range from 0 to 10 ppm. The magnetic field sweep, generated by the potentiometer, is a ramp that varies from about -3.10 V a t 10 ppm to 0 V a t 0 ppm. After each of the 4000 pulses, the Y-axis value (spectrum amplitude) is plotted on the recorder (10). An NMR spectrum can he recorded and stored by a computer, if after each of the recorder's 4000 X-axis positions the computer can measure and record the Y-axis value. On the EM-360 NMR, the Y-axis (spectrum amplitude) is ac-
' ADALAB is a trademark name of Interactive Microware Inc., P.O.
Box 139. State College, PA. 16804.
cessed through connector P 4 (the oscilloscope connector) located a t the rear of the instrument console. This was connected directly to the AID converter on the ADALAB interface card. Writing a program to collect the Y-axis value after each of the 4000 X-axis pulses is an extremely difficult task because the timing of the data collection by the program must perfectlv coincide with the seauence of the 4000 pulses for the x-axis. This problem can be solved if the computer either generates or controls the magnetic field sweep, and thus controls the X-axis values. Control of the X-axis was accomplished by minor modification of the EM-360 and the construction of the difference and inverting amplifiers, Figure 5. T o control the X-axis, it was necessary for the computerto generate a 4000-step ramp that ranged from -3.10 V to 0 V. The ADALAB interface card had a 12-hit (212or 4096 steps) D/A converter which was nearly ideal for producing the appropriate ramp. A major problem with the D/A converter was that its signal was symmetrical +2 to -2 V, as opposed to the needed values of -3 V to 0 V. The DIA converter was connected to a difference amplifier (which had a 2-V reference) and then to an inverting amplifier. By using avariable resistor in the circuit as the feedback resistor on the inverting amplifier, i t was possible t o vary the ramp from -3.10 to 0 V. The output from the inverting amplifier was then connected to the magnetic field sweep of the EM-360 via a single-throw-double-pole toggle switch. The field sweep potentiometer. which eenerates the maenetic field sweep. is located at the left rear of the recorder cf you are standing in front of the console) and can onlv he accessed hv removine the console cover. T o make the connection hetwien the inverting amplifier and the magnetic field sweep, you must unsolder thk wire connected tothe "wiper"of the fikld sweep potentiometer and then connect this wire to the middle post of the SPDT switch. A wire was then soldered to the "winer" of the field sweep potentiometer and connected to either of the remaining posts on the SPDT switch. Finally, the inverting amplifier is connected to the remaining post on the SPDT switch. With the SPDT toggle switch in position 1, the EM-360 will operate as usual. In position 2, all the controls on the EM-360 willoperate, hut the Y-axis (pen) will not respondas the pen carriage is moved left or right. The Y-axis is still connected, hut the X-axis has been disconnected and the magnetic field sweep is no longer controlled by the recorder of the EM-360. Instead i t is controlled by the computer. The actual program for signal averaging is extremely simple (less than 20 BASIC lines). The initial step is the dimensioning of arrays and configuring the ADALAB interface card. Using a loop, the X-axis is generated using the DIA converter and the Y-axis value is recorded using the A D converter. When all the data has been collected. it is "mani~
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DIFFERENCE AMPLIFIER
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~
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INVERTING AMPLIFIER
Figure
5. Schematic diagram for difference and inverting amplifiers. This Circuit is used to convert the +2-(-2)voltage of the D/A convertertoa (-3t0
wit ramp.
Volume 63
Number 12
December 1986
1073
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t 5"
I
I
I
INSIDE iR-337
Figure 7. Schematic diagram of external planer attachment and screw terminal box for Perkin-Elmer Model 337.
Figure 6. NMR spectra of dilute ethanol: A) 1 scan recorded under " m r m l " conditions; El) 30 scans collected, signal-averaged,and plotted by the computer.
pulated" so that the tallest peak (we assume TMS will always be the tallest peak) is placed in array position 3400 (the choice of this array position is somewhat arhitrary). By makine TMS the lareest - neak . in the snectrum and hv alwavs plating it in the same array position; we have eliminated the need for a signal lock feature on the EM-360 NMR. The computer the.,, collects the next scan of the sample. It then shifts thearray positionsso that TMS isat onsition 3400and adds the scan-to the previous scan. This process continues until the desired number of scans have been collected and added together. The data is then scaled, with TMS being scaled separately and plotted on the X-T recorder or an X-Y plotter. TMS is scaled separately because it is usually so much larger than any other peak in the spectrum. Thus in the final spectrum all peaks are approximately the same height. If desired, the program can be expanded t o include integration of the spectrum and storage of the spectrum on a disk. Typical results are shown in Figure 6. The NMR spectrum shown in Figure 6A is a sample of dilute ethanol in carbon tetrachloride. The ethanol peaks are almost unobservable, whereas the TMS peak is easily discernible. The spectrum shown in Figure 6B is the same sample after collecting and averaging 30 scans. The ethanol peaks are easily observed; however, the amplitude of the TMS signal has not changed due to the scaling of this peak by the program.
Perkin-Elmer Model 337 Infrared Spectrophotometer Interfaced to an IBM PC Myrna S. Pearson Wheaton College Norton. MA 02766 Salvatore J. TUZZO Tuzzo Englneering Associates Norton, MA 02766
In an attempt to respond to the trend toward computerbased laboratory automation, management, and networking, our chemistry department opted to initiate a program of interfacing its current instruments to an IBM PC, beginning with the Perkin-Elmer Model 337 Infrared Spectrophotometer. Initially the following equipment was purchased: an IBM PC system unit with dual disk drives and 192K RAM, IBM DOS 1.1,a colorlgraphics card, a colorlgraphics monitor and adapter, a graphics printer (Epson RX-100) and 1074
Journal of Chemical Education
CIRCUIT 15 MOUNTED IYSlOE SCREW IERIIINAL BBI Figure 8. Schematic diagram of circuit mounted insids screw terminal box to generate interrupt pulse.
adapter, and a MetraByte Data Acquisition and Control System ($607 with accessories). The major component in the MetraByte system is the DASCON-1 data acquisition and control interface board (model no. DASOI), multifunction analog and digital inputloutput board designed to plug into one of the expansion slots inside the IBM PC. This board enables the IBM PC to control low speed (30 samplesls, integrating) A/D data acSign. Additional quisition with a resolution of 12 Bit DASCON-1 accessories required for the project include a screw terminal hoard (model no STAOI), which allows all the functions of the DASCON-1 t o be accessible to the user externally with a minimum of wiring and affords easy status checks of the digital I10 lines through the use of lightemitting diodes, and a ribbon cable (model no. C1800) to connect DASCON-1 to the screw terminal hoard. The Perkin-Elmer Model 337 Infrared Spectrophotometer is a double-beam grating instrument that covers the range 4000 to 400 cm-' using two gratings (one operating from 4000 to 1200 cm-' and the other from 1333 to 400 cm-'). Thus, two scans and two data files are required to store the entire spectrum for any given compound. With our system spectra are recorded using a linear frequency (cm-') ahscissa presentation and a linear ordinate scale in percent transmittance while employing the slow (24-min) scan for maximum resolution.
a
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