Continuous-flow spectrophotometric determination of sulfadiazine by diazotisation with in situ preparation of nitrite

Nitrite is prepared in situ for the determination of sulfadiazine. The method is based on solid-phase reduction of copperized cadmium of nitrate; the nitrite reagent merges with the sample stream in hydrochloric acid medium and the resulting mixture is injected into the water carrier, pure distilled water, and then merges with the N-(1-naphthyl)ethylendiamine reagent and is measured spectrophotometrically at 542.0 nm. The calibration graph is linear over the range 0.5–50 μg ml−1 sulfadiazine, mid-range R.S.D. = 0.3% (n = 5) and sample throughput 72 h−1. The procedure is applied to sulfadiazine determination in a pharmaceutical formulation and to in vitro dissolution studies of two different pharmaceutical formulations. The method makes the frequent preparation of the unstable nitrite solution unnecessary; the physical and chemical characteristics as well as the life-span of the solid-phase reactor are also studied.