Determination of ranitidine in pharmaceutical preparations using manual and flow injection potentiometry and spectrophotometry

New, simple and convenient potentiometric and spectrophotometric methods are described for the determination of ranitidine. The potentiometric technique is based on direct measurements of the drug cation with novel PVC matrix membrane sensors incorporating ranitidine-reineckate, tungstophosphate and tungstosilicate ion association complexes as electroactive compounds with a-nitrophenyl phenyl ether as plasticizing solvent mediator. These sensors exhibit rapid near-Nernstian stable responses for 10(-2)-10(-6) M ranitidine over the pH range 4-8, and are used in a flow-through sandwich cell for flow injection determination of the drug. The spectrophotometric method involves the formation of a yellow di(N-nitroso)ranitidine chromophore by reaction of ranitidine with excess nitrite in acetate buffer of pH 4.8 and in the presence of Cu2+/Br- or micelles as catalyst. Beer's law is obeyed at 450 nm over the range 0.3-12 mg ml(-1). Determination of ranitidine in a variety of pharmaceutical dosage forms using the proposed potentiometric and spectrophotometric methods shows an average recovery of 98.4% of the nominal values and a mean standard deviation of 0.5%. No interferences are caused by various drug excipients and diluents. The results compare favourably with those obtained by the liquid chromatographic method of the US Pharmacopoeia.