Flow-injection determination of nitrites based on their reaction with thiocyanates

A technique for the flow-injection determination of nitrites with spectrophotometric signal detection was developed and studied. Additionally, a combination of the developed technique with the on-line preconcentration of low concentrations of nitrites in surface and potable waters was investigated. The technique is based on the reaction of nitrites with thiocyanates. The product of the analytical reaction (nitroso-S-thiocyanate) and its adducts with strong acids are stable in aqueous solutions, which is supported by quantum chemical calculations. It is shown that the reaction chosen is attractive for analytical applications, because it is highly selective. A decrease in the detection limit down to 1.5 ng/mL (3s) is achieved by combining FIA with on-line ionexchange preconcentration. The technique developed is used for monitoring nitrites in natural and waste water. The throughput capacity is 300 samples per hour.