INVESTIGATION OF RESPONSE FACTOR RUGGEDNESS FOR THE DETERMINATION OF DRUG IMPURITIES USING HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY WITH ULTRAVIOLET DETECTION

Quantification of impurities in drug substances and dosage forms using HPLC assays with UV detection is often done by comparison to a standa rd of the drug itself. Depending on the spectra of the compounds invol ved, small changes in wavelength may cause response factors to vary fr om day to day and instrument to instrument. Lack of assay ruggedness w ith respect to wavelength can lead to poor reproducibility of results. Response factor ruggedness was investigated for potential impurities in LY297802 tartrate, a potent muscarinic agonist. The UV responses of some impurities at 280 nm, the analytical detection wavelength, diffe r from that of the parent and change significantly with small shifts i n wavelength. The ruggedness of response factors was examined on a sin gle detector and among several different detectors. Results varied sig nificantly among the different detectors. The UV spectra of the impuri ties could be used to predict the effect of wavelength on ruggedness o f response. A wavelength system suitability sample is proposed as a wa y to overcome variability due to small differences in detector wavelen gth.