A low cost, open and flexible on-line 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 commercial integrated circuits, namely a programmable gain amplifier and an analogic low pass filter, and a regular PC compatible computer. The lack of time counting circuits in the board has been solved by the use of the pulse generation circuit of the personal computer as reference time for the acquisition rate. Thus, one channel of timing of this circuit has been reprogrammed to work at frequencies higher than 18.2 Hz when needed. In addition to its low cost, the system is open and flexible. It may process either internal data or files generated by other systems, it allows the easy insertion of more software routines for data treatment and contains a wide diversity of methods for data quantitation 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 equations and curve fitting of different distribution functions by the generalized least squares method. The last method affords the use of the Gaussian, Exponentially-Modified Gaussian and log-normal functions as well as the orthogonal developments of the former, the Gram-Charlier and Edgeworth-Cramér series.