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 interest. the backmound or baseline beneath this peak must he enlmlated. Option 5 provides either a linear or nonlinear rthird.order) dctermination of background In the case oi a linear fit, the beginning and end of the peak must be 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 ealculations or changed via a cursor in the event tbat background was calculated under two or more peaks that were not completely resolved. Fimrre 2 shows the neak of interest after backbound subtraciion and illustrates the method by which rhe intepatron is performed. The peak area, height, wrdth, and retention time are then printed out. Once tbis 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 particular peak has been analyzed, it is removed from the chromatogram and replaced by theralrulated hackpound. Options not described in the above discussion include the smoothing 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 bard copy of the chromatogram with option 7. The following printers/interfaces are supported with respert ro the hard ropy option: (1) Image Writer with Super Serial card.. (2) ~ ~ l Interface. er and (3) . . G r a.. Silentype printer. I believe tbat for student use. this tvme , of interactive prupam is superiur to automatic integrators and I have incorporated it and the asswiated data collection software into several existing chromatographic experiments. Both the data acquisition and analysis programs have sparked an interest in many of my students as has been evident from their questions and enthusiasm in usine the oroeram. .. Their ouestions bave often led to further work such as the comparison of calmlnred data hefore and after smoothing 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
Optlons Available wlth "CHROMANAL" (revieve data from disk) (plot chr~n~togramon hl-res s m n ) (plot pan at chromatagram) (direct wtput to printer) (linear or nonlinear In) (calculatearea, height. and width) (hires screen to printer) (7-point polynomial s&) (save presently viewed data on disk)
l...GETDATA
2 . . . PLOT DATA
3 . . .CHANGE WINDOW 4 . . .TMXjLE PRINTER 5..
.FIT BACKGROUND
6 . . . INTEGRATE
7 . . .HARD COPY
8 . . . SMOOTH DATA 9 . . . SAVE DATA
#8551332). Information on the software described, including the data arquirition pro-
grams, may be obtained from rhe author.
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Computer-InterfacedDigital Counter-Analogue Data Acquisition System and Demonstration of Signal-toNoise Enhancement Methods
Figue 1. ion chromatowphy after expansion of region m i n i n g me ammonium and potassium peaks. Solid lines Indicatethedata on balh sides of lhe peak$ uaed to calculate lhe backwuound.
~eparbnemof BlophVsics UniverriQ 01 Virglnia Char onasviiis. VA 22901 J. N. Dernas, and Mawln Grubb Depamem of Cheminry UniversiQ at Virginia Charlottesville.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-counter-ratio meter and an analogue interface based on a voltage-tofrequency converter (VFC). The system is used to implement a low-speed transient recorder. SIN . enhancement hv dieital integration and ensemble averaging are demonstrated as well a i the suppression of €&Hz noise by integration. The system is built around an IntersilIGE Universal Digital Counter Demonstrator. The kit (
