Spectrophotometric determination of dipyrone in pharmaceutical preparations by using chromotropic acid

A spectrophotometric method for the determination of dipyrone in pharmaceut ical preparations is proposed. This method is based on selective oxidation of dipyrone, in the presence of sulphuric acid, splitting off formaldehyde which reacts with chromotropic acid, also in a sulphuric acid medium, produ cing a violet-red compound (lambda(max) 575 nm). Beer's law is obeyed in a concentration range of 0.57-5.7 ppm dipyrone with an excellent correlation coefficient (r = 0.9997). The results show a simple, accurate, selective an d readily applied method to the determination of dipyrone in pharmaceutical products. The analytical results obtained for these products by the propos ed method are in agreement with those of the Brazilian Pharmacopoeia proced ure. No interference was observed from common excipients in formulations. R ecoveries were within 98.7-101.2%, with standard deviations ranging from 0. 2 to 1.7%. (C) 1999 Elsevier Science S.A. All rights reserved.