An unknown impurity in the fermentation-based drug substance lovastatin at 0.52 RRT was observed invariably in all batches when analyzed by HPLC as per the PhEur monograph. This impurity was isolated from the impurity-enriched sample using reversed-phase preparative HPLC and characterized by using spectroscopic (PMR, CMR, MASS, and UV) techniques as the structurally-related compound Monacolin-X, having the molecular formula C24H34O6 and the chemical name 2-methyl-3-oxobutanoic acid 1,2,3,7,8,8a-hexahydro-3,7-dimethyl-8-[2-(tetrahydro-4-hydroxy-6-oxo-2H-pyran-2-yl)ethyl]-1-naphthalenyl ester.

A improved, simple and economic reverse phase high performance liquid chromatography (RP-HPLC) method has been developed and validated as per ICH guidelines for the quantification of acetic acid present in Gefitinib as an solvent impurity. Validation studies demonstrated that the proposed RP-HPLC method is simple, specific, rapid, reliable and reproducible. The high recovery and low relative standard deviation confirm the suitability of the proposed method for the routine quality control analysis for the quantification of acetic acid in Gefitinib.

An unknown impurity in the bulk drug daunorubicin hydrochloride observed at 1.79 RRT was detected by the means of reverse phase isocratic High performance liquid chromatography (HPLC). This impurity was isolated, enriched and was subjected to mass and NMR spectral studies. Based on the spectral data the impurity was identified as (8S,10S)-8-ethyl-10-[(2S,4S,5S,6S)-4-amino-5-hydroxy-6-methyl-oxan-2-yl]oxy-6,8,11-trihydroxy-1-methoxy-9,10-dihydro-7H-tetracene-5,12dione also known as 13-deoxy-daunorubicin.