Flow-injection spectrophotometric determination of salbutamol with 4-aminoantipyrine.

A flow-injection method is proposed for the determination of salbutamol. The method involves the condensation of salbutamol with 4-aminoantipyrine in the presence of hexacyanoferrate (III) in alkaline medium, producing a coloured quinoneimide that was detected absorptiometrically at 500nm. The values of four variables (two reactor lengths and two reagent concentrations) were optimised by means of the sequential simplex method and their influence studied in univariant way. The method was validated and compared with the HPLC method established in the United States Pharmacopeia (USP). Linearity was demonstrated in the range 0-74.1mg/L of salbutamol sulfate (r(2) = 0.9999). Commercial samples of pharmaceuticals containing salbutamol sulfate (tablets and oral solutions) were analysed and the results obtained with the proposed method agreed with the USP method in less than 1.6%, with precision similar to the HPLC method (1%-2% R.S.D.). The sampling frequency was 75 samples/hour.