Qualitative Analysis

 

An impression of the analysis of a mixture of two substances, perchlorate and p-amino benzoate that has been monitored by a potentiometric detector is depicted in figure 18. The same type of isotachopherogram would have been obtained by monitoring potential gradient (E), the temperature (T) or with the use of a conductometric detector (R).

 

Figure18. The Analysis of a Mixture of Two Substances, Perchlorate and p-Amino Benzoate Monitored by a Potentiometric Detector for Qualitative Purposes

 

In figure 18, the linear trace is produced by the potential detector and the heights of the steps provides qualitative information and the step lengths which are accurately provided by the differential trace give quantitative information.

 

There are four different measures that are employed for qualitative interpretation, these measures are given as follow,

 

1                          The Step Height (h_x)

2                          The reduced Step Height (h_x- h_L)

3                          The Step height Value (SU value) i.e.  SU = 100h_x/(h_L

4                          The Reference unit value (RU)  i.e.

The simple step height measurement is not to be relied upon for high accuracy the step height unit value is to be preferred. Actually, a correction is made for electronic amplification but this is also true for the reference unit value. The reference unit depends less on the current density than the step height value and thus, may provide a greater accuracy. It is clear that when quoting qualitative results the operating conditions must be clearly defined so that the validity of the conclusion can be assessed.