Spectrophotometric flow injection procedure to indirect determination of paracetamol in pharmaceutical formulations using o-tolidine as reagent

A spectrophotometric flow injection method for the determination of paracetamol in pharmaceutical formulations is proposed. The procedure was based on the oxidation of paracetamol by sodium hypochloride and the determination of the excess of this oxidant using o-tolidine dichloride as chromogenic reagent at 430 nm. The analytical curve was linear in the paracetamol concentration range from 8.50 x 10-6 to 2.51 x 10-4 mol L-1 with a detection limit of 5.0 x 10-6 mol L-1. The relative standard deviation was smaller than 1.2% for 1.20 x 10-4 mol L-1 paracetamol solution (n = 10). The results obtained for paracetamol in pharmaceutical formulations using the proposed flow injection method and those obtained using a USP Pharmacopoeia method are in agreement at the 95% confidence level.

Flow injection analysis of vancomycin

A flow injection method for the quantitative analysis of vancomycin hydrochloride, C66H75Cl2N9O24.HCl (HVCM), based on the reaction with copper (II) ions, is presented. HVCM forms a lilac-blue complex with copper ions at pH≅4.5 in aqueous solutions, with maximum absorption at 555 nm. The detection limit was estimated to be about 8.5×10-5 mol L-1; the quantitation limit is about 2.5×10-4 mol L-1 and about 30 determinations can be performed in an hour. The accuracy of the method was tested through recovery procedures in presence of four different excipients, in the proportion 1:1 w/w. The results were compared with those obtained with the batch spectrophotometric and with the HPLC methods. Statistical comparison was done using the Student's procedure. Complete agreement was found at a 0.95 significance level between the proposed flow injection and the batch spectrophotometric methods, which present similar precision (RSD: 2.1 % vs. 1.9%).