Difference Between PURITY, ASSAY & POTENCY

 

Purity:

 

It is calculated by area normalisation method, it can be directly find out by chromatograms obtained from HPLC.

 

% Purity = (Area of desired peak / Sum of area of all peaks) x 100

 

Assay:

  

It is calculated against standard. It may be of following types:

 

1) On as is basis = (Area of sample / Area of standard) x (conc. of standard / conc. of sample) x potency or assay of standard

2) On anhydrous basis = (Assay on as is basis / 100 – moisture) x 100

3) On dried basis = (Assay on as is basis / 100 – LOD) x 100

 

Potency:

 

 100 – (moisture or LOD + residual solvents + heavy metals + sulphated ash + impurities)