A sensitive flow-injection method for determination of trace amounts of nitrite

A new sensitive colour reaction for nitrite determination is presented. In acidic medium, nitrite was reacted with safranine to form a diazonium salt which caused the reddish-orange dye colour of the solution to change to blue. The carrier stream, into which the sample solution was injected, was doubly distilled water. The reagent solution stream, which contained safranine dye, hydrochloric acid and potassium chloride, was mixed with the carrier in a 3-m length of silicon tubing (bore 0.5 mm) maintained at 30°C in a thermostatic bath. The absorbance intensity was measured at 520 nm. The detection limit was 20 ng ml^?1 and the RSD% of 20 injections of 1 μg ml^?1 of nitrite was 0.65%. Analysis can be done at a rate of up to 30 h^?1. Under the optimum conditions in the concentration range of 30–4000 ng ml^?1 of nitrite ion, a linear calibration graph was obtained (r=0.9999). The method was applied successfully to the determination of nitrite in sausages.