Figure 8. Liquid chromatogram of a mixture of hydroxybenzaates.
An Inexpensive Microcomputer-Based Data System for Liquid and Gas Chromatography Charles 6. Pate1and Harvey 6. Herman University of North Carolina at Greensboro Greensboro. NC 27412 Digital computers have become commonplace in the science laboratory (31,32,33,34). They are used principally for data acquisition, experimental control and computation in chemical research applications. The advent of inexpensive microcomputer systems has made it possible for even a school with a modest budget to introduce digital computers into the undergraduate chemistry laboratory curriculum (33). We report here the use of a small computer for data acquisition and computation. In this application the computer will be used for on-line data acauisition from a gas or licluid chromatograph. Even with minimum system (8Kbytes) we can demonstrate post-run computation of peak area, peak height and retention time on smoothed data. A general discussion of computer applications in gas chromatography can he found in refeience (35).
a
Hardware The microcomouter (Commodore PET, 2001, Palo Alto, CAI was equippch with the standard 8K bytes of RAM and the "old" ooeratinr system. An S-100 motherhoard, HVI'SI c ore thought ~ro&ts, Eugene, OR) was used to adapt the analog-to-digitalconverter (Precision Analog Interface, Vector Graphics, Westlake Village, CA), to the microcomputer. We installed a computer controlled track-and-hold circuit (c.f., ref. 36) between the analog interface and the amplified chromatograph signal. A microvolt amplifier (Keithley, Cleveland. OH) was used to scale the output of the chromatograph td2.5 V full scale. The total cost >the above was less than $1500 excluding the microvolt amplifier. Software The analog-to-digital conversion of the signal from the chnnnatograph is accomplished with an assembly language program that convert< the analog input (range t5 V to -5 V J t o a dieitul 12-bit scale (ranee 0 t o 1096) hy the successive approxTmations method. Theexecution time for array storage of one conversion is approximately 12 ms. All other programs are written in BASIC and overlayed when needed. Data may be saved or loaded from cassette tape with ~~
~
' On leave from Salem College, Winston-Salem, NC 27108. 244
Journal of Chemical Education
Table 2. Comparlson of Computer Calculations and Manual Measurements.
Peak
1 2
3 4 5 6
Liquid Chromatography Peak Height Retention (Rella peak 3) Time (MIN) A B A B
3.31 0.23 10.0 6.75
3.59
