Spectrophotometric determination of metamizol in pharmaceutical formulations by flow injection triiodide generation.

A flow injection spectrophotometric procedure was developed for the determination of metamizol in pharmaceutical formulations. The system is based on the reaction between metamizol and triiodide generated in the system by mixing iodate and iodide-starch solutions. The absorbance of triiodide-starch complex giving a steady-state baseline value which was monitored at 580 nm. The inverse peaks caused by metamizol samples were measured and there was a direct relationship between absorbance decreasing and metamizol concentration from 1.4 x 10(-4) to 7.0 x 10(-4) mol L-1. The RSD was 0.45% for a metamizol solution 4.2 x 10(-4) mol L-1 (n = 10) with a detection limit (three-fold blank standard deviation/slope) of 6.0 x 10(-5) mol L-1 The feasibility of the system was demonstrated for the determination of metamizol in commercial samples with sixty results obtained per hour. The results obtained for metamizol in pharmaceutical formulations using the proposed flow procedure and those obtained using an iodimetric procedure are in agreement at the 95% confidence level and within an acceptable range of error.