A sensitive and rapid extraction-spectrophotometric method for the determination of betamethasone. based on the formation of a charge transfer
complex with benzocaprol red (I) and acid ethyl blue (11) is described. The calibration graph, resulting from the measurement of the absorbance of the chloroform and benzene extracts (10 ml) at 588 and 677 nm using I and 11, respectively, is linear over the range 0- 16 and 0-20 pg ml-1 of betamethascne with relative standard deviations (R.S.D.) of 1.6 and 1.3% for 5 pg ml-' betamethasone using reagents I and 11, respectively. For more accurate results, Ringbom optimum concentration ranges were found to be 2-14 and 2-17.5 pg ml-' using reagents I and 11, respectively. The method was satisfactorily applied to the determination of betamethasone and its esters in pharmaceutical preparations and found in good agreement with the British Pharmacopeia (1993) method.
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