Quantitative Analysis

In figure 19, the same analysis is displayed. The linear trace is produced by the potential detector but the widths of the steps (as opposed to the step heights), provides the quantitative information the magnitudes of which, are accurately provided by the differential trace.

Figure 19. The Analysis of a Mixture of Two Substances, Perchlorate and p-Amino Benzoate that are Monitored by a Potentiometric Detector.

The relationship between the zone lengths and the quantity of ion species introduced into the system is linear assuming the current is constant and well stabilized. For accurate quantitative results calibration curves should be constructed covering the concentration ranger of interest and example of which is given diagrammatically in figure 20.

Figure 20. A Calibration Curve Obtained from a Set of Standard Isotachopherograms

If the mobility and the pK_a of an ion are known the calibration curve can be determined, An internal standard can also be employed if so desired and can provide equally accurate results. In general, however, it is better to work using calibration curves for reliable and constant accuracy.