TRS-80 simulation of a gas chromatographic separation

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Our program introduces the student to the basics of column selection and the optimization of separation conditions. It has heen designed principally for use in juniorlsenior level analytical chemistry courses. Chromatography theory, gas chromatography equipment, and the basics of column design should he discussed in class prior to running the program. It is also helpful if the students have had some GC experience in lab. The program is conducted in three steps: 1) Column Design. The student is allowed to "create" hisiher own column for the separation of a three-component mixture. In this step, the support mesh size and a stationary nhase must be selected from a limited set. The choice of stationary phase determines the separation factors for the three species. The percent by weight of the stationary phase and the column length (in feet) are also selected. The rationale behind using mesh size, percent by weight of stationary phase, and column length in feet is that this is how columns are typically listed bv manufacturers. 2) ~ k n p e r a t u r eand Flow Rate Optimization. Once the column has been produced. the oven's operatine temperature and the carrier gas flow rate are requested. he temperature range is limited by the T,;, and T,, of the stationary phase as well as the oven limits (23-299°C). Flow rates are limited to a 1-200 mL1min range. Once all parameters have been selected a chromatogram is displayed on the CRT. The retention times of the peaks representing the three species, the resolution of the peaks, a s well as the selected operating parameters are also displayed. To make the simulation even more realistic, the actual costs of all supplies are given and the column cost calculated. If more than one column is produced, the total costs are calculated. The rate,at which the chromatogram is drawn on the screen is a function of the t , of the last peak. This is a way of making the student aware of the fact that good resolution a t the expense of long retention times is now always desirable. The student then has the option of changing the temperature or flow rate, making a new column, or obtaining a printout. The object is to obtain a resolution greater than 1.5 for the peaks. When this occurs, the student is prompted with "QUANTITATIVE SEPARATION ACHIEVED." 3) Print Out. When requested, a listing of the final column its cost and the total costs are given. The HETP, t,, numher of theoretical plates and peak widths for each species, as well as copy of the final chromatogram, are also listed. This program allows the student to become more aware of the choices involved in designing a gas chromatographic separation. Presenting the data graphically enables the student to see the effect(s1 of hisfher decisions. Even though a

single three-component mixture is to be separated, the likelihood of anv two students develonine . the same senaration parameters (same chromatogram) is remote. This is because each student has the ootion of usine seven different stationarv phases and six differknt solid support mesh sizes. Each df these parameters has a dramatic effect on the ability of a column to separate the mixture. Also there are the other variables that influence the performance of the column(s) designed. This program is written in Level 11 BASIC for a TRS-80 Model 111 and a Model VII Line Printer. With instructions and comment lines, the program requires 10K for execution. Documentation, including a program listing, sample executions, and comments, is available for $2.00 by writing Dr. J. K. Hardy. Checks should he made payable to The University of Akron. A disk copy can be obtained for the TRS-80 Model 111 if a properly formated disk is supplied (5% inch, 40 track disk). This disk must already be initialized with TRSDOS1.3 or LDOS 513lR.

Display of Vapor Pressure Data with a Theoretical Fit James M. Grow

New Jersey Institute of Technology Newark, NJ 07079 A microcomputer with a large color monitor can he rolled into the classroom and used as easily as an overhead projector once the appropriate programs are written. Several programs written in Pascal for the Apple computer have been designed to aid the teacher in just such a classroom presentation. PASCAL was chosen to obtain as much transportability of the oroeram as oossihle. Also.. eranhics and disk storaee of " . info;mkon is easier in PASCAL, and the structure used in coding PASCAL makes the code more readable. The first program is a simple program to show the use of two models, Antoine's (In(P) = A - R I ( T C)) and Clausius-Clapyron's R ) , to predict the vapor pressure ( P ) (ln(P) = - LW,.,IRT of a single component system a t temperature T. The mailing program which came with the Pascal language, Apple3: DISKIO, was modified to include different information in its standard record. The string variables which contained the address information in the mailing program were changed to real numher variahles which contained temperature and Dressnre data from the "Handbook of Chemistry and Physics." Antoine's constants and the heats of vap&ation &e placed in another real numher array of the record. The procedures to zero the record, toshow the record, and to change the record were modified to include the new variable. These modifications allowed the vapor pressure data for many systems to he stored easily on disk. This information can he retrieved in the classroom and used to illustrate the accuracy of a given model for any number of systems through graphical display on the monitor. A sample display is given in Figure

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Figwe 1. Fit of vapor pressure cycloherane as a function of temperature using Antoine's equation.

1062

Journal of Chemical Education

Vanor pressure data for hinarv svstems can he stored on disk and retrieved in the classroom just as easily. The standard record can be chaneed to include the hoiline temueratnres as well as the compo$ition of both the liquid'phask and vapor phase for a niven temDerature. Both van Laar's and Raoult's ~ a can w h e k e d to model the boiling points and dew points for anv composition of anv numher of hinarv systems. In either case Antoink's constants are used to calcul&the temperature dependencv of the vapor pressure for each of the components. he correci boiling temperature is determined by inte;actively calculatinr the temperature a t which the sum of these pressures equals atmosiheric pressure. This type of problem is of considerable concern in industrial separations such as distillation. Again, the procedures to zero the records, change the records, and plot the data along with the various models must he