I got 88.0 % assay for a drug in HPLC analysis for same
injection i got 40.0% related substances is it possible?
what is the relation between results of assay and purity?

Answer Posted / s chatterjee

in Gabapentin, Imp A has a RRF of 12.6 i.e. against gabapentin standard. Say Gabapentin has degraded 12 % i.e. 88 % assay ( quantitative only) . When rel subs was calculated the Imp A against the gabapentin standard will give an quantitative value of 36 %. however, in reality as the correction factor is 12.6 then this comes to 36/12 = 3 % in reality.

Therefore it is important to know that the correction factor of related substances had been established against the drug used for quantification. Response of degradation products varies significantly from the drug candidate under UV.

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