Simultaneous Determination of Mixtures of Nitrite and Nitrate by Reversed-Phase Ion-Pair Liquid Chromatography

To overcome the relatively low resolution in the separation and quantitative analysis of mixtures of nitrite and nitrate, a reversed-phase ion-pair liquid chromatographic method is developed with advantages of high accuracy, good selectivity, high efficiency, and low cost. By employing cetyltrimethylammonium bromide (CTAB) as the ion-pair reagent, this method can work excellently in situations where one component in the mixture is highly in excess (e.g., molar ratio of n( NO2−):n(NO3−) ranging from 1:99 to 95:5). The operation parameters were optimized on a Shim-pack VP-ODS(150 L × 4.6) analytical column using a methanol/water ratio of 50:50 (v/v) mobile phase containing 7.0 mmol/L CTAB and 3.1 mmol/L potassium dihydrogen phosphate (KH2PO4).The column works at a temperature of 35 °C with a flow rate of 1.5 mL/min. Such a protocol can be applied to monitor the formation of trace nitrous acid during the oxidative decomposition of nitric acid.