Quantitative Analysis with GC and HPLC

The physical size of a peak, or area under the peak, traced on the chromatogram is directly proportional to the amount of that particular component passing through the detector. This, in turn, is proportional to the concentration of that mixture component in the sample solution. It is also proportional to the amount of solution injected, since this too dictates how much passes through the detector. The more material being detected, the larger the peak. Thus, for quantitative analysis, it is important that we have an accurate method for determining the areas of the peaks. 

A given amount of one component will not produce a peak the same size as an equal amount of another component, however. This will be discussed further in Chapter 12, Section 12.8.2. 

The modern analytical laboratory employing instrumental chromatography uses a computer data collection system and associated software to acquire the data and display the chromatogram on the monitor. Parameters important for qualitative and quantitative analysis, including retention times and peak areas, are also measured and displayed. The software can also analyze the data to determine resolution, capacity factor, theoretical plates, and selectivity. 

Kronschnabel of the City of Lincoln, Nebraska, Water Treatment Plant Laboratory examines a chromatogram displayed on a computer monitor. 

FIGURE 11.20 An illustration of how the area of an instrumental chromatography peak is determined by integration. The series of digital values acquired by the data system, represented by the vertical lines, are summed. 

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