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Philosophy of Qualitative analysis and Quantitative analysis by chromatography

Qualitative analysis

A standard sample of aspartame was measured, yielding a peak at 12.5 minutes. This peak corresponds to aspartame, itself.
Next, a sample prepared from a beverage was measured under the same conditions, yielding a number of peaks. The peak appearing at 12.5 minutes can be regarded as that of aspartame (Figure 1).
The following conditions were the same: the type of fillers, column sizes, column temperature, composition of the mobile phase, and flow rate.


Figure 1. Example of aspartame measurement

Quantitative analysis

The height and area of a peak are proportional to the concentration of the corresponding component. A calibration curve is created using the standard sample. The concentration of aspartame in the beverage can be determined from the peak area of the detected aspartame.

Attention should be given to the fact that a qualitative analysis includes many uncertainties. Other components may have been eluted together with aspartame. LC and GC systems are good at determining the content of a certain component in a sample, rather than the types of the components of a sample. Performance of a quantitative analysis requires the preparation of a calibration curve. It is very difficult to perform the qualitative or quantitative analysis of a component for which a standard sample is not available.