HPLC AND NMR METHODS FOR THE QUANTITATION OF THE (R)-ENANTIOMER IN (-)-(S)-TIMOLOL MALEATE DRUG RAW-MATERIALS

HPLC and H-1-NMR methods for the quantitation of the (R)-enantiomer in (-)-(S)-timolol maleate were developed and validated. The HPLC method requires a 25 cm x 4.6 mm 5 mu m Chiracel OD-H (cellulose tris-3, 5-dimethylphenylcarbamate) column, a mobile phase of 0.2% (v/v) diethylamine and 4% (v/v) isopropanol in hexane at a flow rate of 1 ml/min and UV detection at 297 nm. A system suitability test was devised to verify the separation of the (R)- and (S)-enantiomers of timolol from other drug-related impurities. The NMR method requires the use of a high-held NMR spectrometer (>360 MHz) and a chiral solvating agent, (-)-(R)-2,2,2-trifluoro-1-(9-anthrylethanol) (R-TFAE). The limits of quantitation were 0.05% and 0.2% (m/m) for HPLC and NMR, respectively. The methods were applied to the determination of the (R)-enantiomer in eight lots of raw material. The results for the two methods were in very goad agreement, with results ranging from 0.1 to 4.1% (m/m) by HPLC and none detected to 4.3% (m/m) by NMR. The USP method for specific rotation was found to be unsuitable for detecting the presence of low levels of the (R)enantiomer in (-)-(S)-timolol maleate. Published 1994 Wiley-Liss, Inc.