A LOW-COST, OPEN AND FLEXIBLE ONLINE DATA-ACQUISITION SYSTEM FOR INSTRUMENTAL CHROMATOGRAPHY

A laboratory-made data acquisition system has been constructed using a low cost acquisition board for industrial applications, a few commerc ial integrated circuits, namely a programmable gain amplifier and an a nalogic low pass filter, and a regular PC compatible computer. The lac k of time counting circuits in the board has been solved by the use of the pulse generation circuit of the personal computer as reference ti me for the acquisition rate. Thus, one channel of timing of this circu it has been reprogrammed to work at frequencies higher than 18.2 Hz wh en needed. In addition to its low cost, the system is open and flexibl e. It may process either internal data or files generated by other sys tems, it allows the easy insertion of more software routines for data treatment and contains a wide diversity of methods for data quantitati on and peak parameter calculation (area, mean, variance, skew, excess and number of theoretical plates). Three different calculation methods for the determination of these parameters are included in the system: additive integration, graphical measurement-based log-normal equation s and curve fitting of different distribution functions by the general ized least squares method. The last method affords the use of the Gaus sian, Exponentially-Modified Gaussian and log-normal functions as well as the orthogonal developments of the former, the Gram-Charlier and E dgeworth-Cramer series.