Page 56 - Quality control of pharmaceuticals (07-PA 704)

3. Specificity (Selectivity):

Selectivity is the extent to which the method can determine particular analysts in a

complex mixture without interference from the other components of the mixture.

A method that is perfectly selective for a particular analyte or group of analytes is

said to be specific.

Selectivity is determined by adding materials that might be encountered in test

samples to the analyte of interest and studying their impact, both individually and in

the presence of other potentially interfering substances (related substances,

degradation products, impurities)

For routine HPLC assay:

Placebo interference

Mobile phase interference

Rt of active (S) in standard solution and test solution (identification)

Acceptance limit:

Up to 1% interference in accepted.

Base line resolution from any peak in the chromatogram is >1.5

Rt for test and standard should coincide together (less than 2% RSD)

Resolution (Rs)

Rs = 2( 2− 1)
2+ 1

Resolution (Rs) is defind as the ratio of the distance between two peaks to the

overage width of these peaks (at baseline)