edited by RUSSELL H. B A n Kenyon College Gambier. OH 43022
Chromanal: Interactive Chromatographic Analysis Software Jeffrey E. Anderson Murray State University Murray, KY 42071 For the past few years I have heen involved in a project to upgrade existing instrumentation by including computer-controlled date acquisition and analysis. This project was initiated to address the following: 1. Most modern instruments contain or are controlled by computers. It is important that students have hands-on experience with camputer-hased instrumentation during their academic careers. 2. Modern computer-based instrumentetion is often automated to the point that Little is left to the analyst. Although this is often the goal, in terms of student use, nothing is leamed of how the analysis is performed or how the instrument works. 3. With the increased importance of computers in chemistry comes the difficulty of introducing various concepts and applications of computers. The problem lies in the fact that courses such as instrumental are already re- ~ ~ - ~ -analvsis ~ sponaihle for introducing an overwhelming amount of material.
students to modify the subroutines or I include a user GOSUE option so that students can easily incorporate other options into the program. I should mention that I do not believe that the nrohlems outlined ahove should- he orean h i entirelv solved withsoftwarp done 1 work clmdy mth the students in the lab and use my software au a tool for introducing various concepts. In the proeess of instructing the students on the use of a particular instrument, I include a discussion of how the computer is controlling the experiment and acquiring data, as well as a discussion of the various options provided hy the software. As implied, my approach and software assume that the instructor is knowledgeable and takes the time to introduce this material. I believe I have heen successful in addressing the ahove issues and in emphasizing that just as instruments are not hlack boxes, neither are computers and software.
The most economical approach to providing students with experience with computer-hased instrumentation is to interface existing instruments. This is a reasonable aproach to addressing item 1 ahove, since often the only difference between outdated instrumentation and "state-of-the-art" instrumentation is the inclusion of computercontrolled data acquisition and analysis. This approach does require the development of the associated software, hut this provides a mechanism for addressing items 2 and 3. In the process of developing software, I attempt to provide a functional program in which much of the decision making is left to the user. The software is menu oriented so the user must go through the step-by-step procedures involved in the analysis of the data. Associated with the various procedures are subroutines that perform the particular operations. I try to encourage students t o look a t these suhroutines to learn how various operations are ~erformed.In some cases, I encourage the
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Journal of Chemical Education
The software described here, CHROMANAL, is an example of my approach to writing software for student use. It is written for Apple computers in Applesoft BASIC and deals with the analysis of chromatographic data obtained from gas or liquid chromatography. CHROMANAL assumes that the actual data collection has already been performed and the data have been saved on disk. For example, I have developed data collection programs for use with the following interfaces: (1) the Isaac 91A interface from Cyborg Inc., (2) the Adalab interface from Interactive Microware, Inc., and (3) the TecMar MadelTM-AD213, 12-bit ADC hoard. All of these data-collection osckaees ~. are written in machine lanwage and Applesoft They do nor use the m BASIC, Labsoft, and Qu~ckI/ extenstons t 0 associated with items I and 2 ahove All of these packages save the resulting data for later analysis with CHROMANAL.
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CHROMANAL is menu operated as may he seen from the table, which lists the options available to the user as well as a brief description of their operation. Perhaps the best way to illustrate the use of this program is through the example analysis that follows. Initially, option 1 is used to retrieve the data from disk, and the data are plotted with option 2. The user can expand a particular region of the chromatogram by moving a cursor to mark the region (window) of interest (option 3). The arrow keys move the cursor and the "M" key is used to place markers enclosing the region of interest. Figure 1 shows an expansion of the peaks due to ammonium and potassium from ion chromatography with a conductivity detector. Assuming that the potassium is of interor baseline beneath this est. the haekeround " peak mu81 he enlculated. Option 5 provides either a linear or nonlinear rthird.orderJ determination of haekground. In the case of a linear fit, the beginning and end of the peak must he specified by the user via a cursor. For a nonlinear fit, regions of data on both sides of the peak must he specified for use in the background calculation. Figure 1 also shows these cursors and the calculated background, Finally, the analysis is completed with option 6. The region to he integrated may he the same as the limits of the peak previously defined for background calculations or changed via a cursor in the event that background was calculated under two or more peaks that were not completely resolved. Fieure 2 shows the neak of interest after background subtraciion and illustrates the method by which the integration id performed. The peak area, height, wrdth, and retention time are then printed out. Once this peak has been analyzed, the user can reset the windows (option 3) to view the entire chromatogram. The user could now proceed in a similar fashion to analyze any other oeaks of interest. I t should be noted that. once a oarticular oesk has been ana-
Optlons Avallable wlth "CHROMANAL" (mblevedata from disk) (plot ChrMnatOgrsmon hi-res screen) (plot pan of chromatogram) (direct ailput to printer) (linear or nonlinear fn) (calculatearea, height and width) (hi-res screen to printer) (7-polnt polynomial stmath) (save presently viewed data on disk)
l...GETDATA 2 .. . PLOT DATA 3.. .CHANGE WINDOW 4.. .TMX*E PRINTER 5.. .FIT BACKGROUND 6 . . . INTEGRATE 7 . . HARD COPY 8 . . . SMOOTH DATA 9 . . . SAVE DATA
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#8551332). Informationon thewftwaredescribed, including the data acqui*ition prugrams, may be obtained from the author.
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Options not described in the shove discussion include the smwthing option in the event of noisy data, and directing data to a printer (option 4). Option 9 saves the data, in the present window, in an alternate format used by other plottingprograms such as Scientific Plotter I1 from IMI. In addition, at any point in the analysis the user may obtain a hard copy of the chromatogram with option 7. The following printerslinterfaces are supported with respect to the hard copy option: (1) Image Writer with Super Serial card, (2) Grappler Interface, and (3) Silentype printer. I believe that for student use. this t m e of interactive pmgram i3 superior to automatic integrators and I have incorporated it and the asswiated data collection software into several existing chromatographic experiments. Both the dataacquisition and analysis programs have sparked an interest in many of my students as has been evident from their questions and enthusiasm in usine the nroeram. .. Their ouestions have often led to further work such as the cumpariron of calculnted data hefore and after smmthing and comparisons of calibration curves generated with linear and nonlinear hackground calculations. Because the program is menu operated and routines are written as suhroutines, modifications are quite easy and have been made by students adept a t
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counter-~nalogue~ a t a Acquisition System and emo on strati on of Signal-toNoise Enhancement Methods
F i v e 1. ion chromatcgaphy alter expansion of region cantaining me ammonium and potassium peaks. Solid lines indlcatethe data on bow sides of Ihe peaks used to calculate Ihe backgrourd.
Dep&m of ~ioph~sics University of Vlrglnie char onssviiis. VA 22901 J. N. Dernas, and Mawln Grubb Depanrnem of Chernisny University of Vlrginia Charlouesville.VA 22901 Computer interfacing can provide powerful measurement tools. Of particular interest are methods of enhancing signal-tonoise ratio (SIN). We describe a simple, inexpensive P C interface f o r a digital frequency-period-couater-ratio meter and an analogue interface based on a voltage-tofrequency converter (VFC). The system is used to implement a low-speed transient recorder. S I N enhancement hv dieital integratian and ensemhle averaging are demonstrated as well as the suppression of 60-Hz noise by integration. The system is built around an IntersiVGE Universal Digital Counter Demonatrator. The kit (
