Liquid Chromatography - Data Acquisition and Processing 2

The output from the detector, usually in millivolts, is passed to a scaling amplifier that converts the signal to a voltage that is acceptable to the analog to digital (A/D) converter The A/D converter changes the voltage output to a binary number which is temporarily stored in a register. This process is continuously repeated at a defined rate, called the 'sampling rate'. The current binary number, stored in the register is regularly sampled by the computer and stored (usually on hard disk). On completion of the analysis the computer accesses all the data from store, calculates the retention report, compares peak heights or peak areas to provide the quantitative analysis according to the processing program that is used and finally prints out the results in tabulated form.

Modern data processing software often includes routines that can process chromatograms where the components of the sample are incompletely resolved. The routines deconvolute the individual peaks from the composite envelope and calculate the area of the individual de-convoluted peaks. Such algorithms can be used very effectively on peaks that are entrained in the tail of a major peak but are not so accurate for composite envelopes containing many unresolved peaks.

It should be emphasized that clever algorithms or subroutines are no substitute for good chromatography.

 

The chromatographic system should, wherever possible, be optimized to obtain complete resolution of the mixture and not place reliance on mathematical techniques to aid in the analysis.