Data Acquisition and Processing System

A diagram of a chromatographic data acquisition and processing system is shown in figure 28.

Figure 28 The Data Acquisition and Processing System

The actual format of the data system can vary widely from manufacturer to manufacturer. Most systems have a means for real time monitoring the detector output, sometimes by using an ancillary recorder, mostly by computer printout. The signal from the detector is first scaled, usually to a range from 0 to 5 volt by a suitable amplifier and the scaled signal is then digitized by means of an A/D converter. The data is then regularly read by the computer and stored on disk. The data may be partially processed 'on the fly' or processed at the completion of the analysis.

Thin Layer Chromatography Apparatus

Thin layer chromatography appears to have been first developed and utilized by Schraiber in 1939 (11). Schraiber working with Izmailov at the Khar'kov Chemistry and Pharmacy Research Institute employed the techniques for the analysis of pharmaceuticals. In her own words,

" It occurred to us that a thin layer of the sorbent could be used in lieu of a strip of paper; also we felt that the flat bed could be considered as a cut-out of the adsorbent column. We believed that in carrying out the separation process in such a layer, the process would be accelerated significantly. In our work, we deposited a drop of the solution being investigated on the flat adsorbent layer and observed the separation into concentric circular zones which could become visible because of their fluorescence in the light of a UV lamp."

Schraiber not only invented thin layer chromatography in 1939 but also was the first to use fluorescence as the separation indicator or detection system. Unfortunately, Schraiber's work does not seem to have been heeded and the technique appears to have been rediscovered by Kirchner in 1951 (12).

Although thin layer chromatography (TLC) phase systems are basically the same as those used in LC , the equipment required is far simpler and very much less expensive. Furthermore, as many separations can be carried out simultaneously by multiple spotting, analysis times are much shorter and there can be as many as 60 samples per plate which, in effect means that each analysis will only take about 5 seconds to complete.

The resolution obtained from TLC is far less than that obtainable by LC but, as a result of the cost advantage, the technique is very widely used. In fact, despite the many advances that have taken place in LC techniques over the past years, the use of TLC for routine analyses continues to grow. However, samples containing multiple components cannot be separated by TLC due to restricted plate capacity. In TLC all the solutes must be contained by the plate whereas in LC, as the solutes are eluted from the column, the component capacity is much greater.