Simultaneous determination of nitrite and nitrate in dew, rain, snow and lake water samples by ion-pair high-performance liquid chromatography

A simple, fast, sensitive and accurate reversed-phase ion-pair HPLC method for simultaneous determination of nitrite and nitrate in atmospheric liquids and lake waters has been developed. Separations were accomplished in less than 10 min using a reversed-phase C18 column (150 mm × 2.00 mm i.d., 5 μm particle size) with a mobile phase containing 83% 3.0 mM ion-interaction reagent tetrabutylammonium hydroxide (TBA-OH) and 2.0 mM sodium phosphate buffer at pH 3.9 and 17% acetonitrile (flow rate, 0.4 mL/min). UV light absorption responses at 205 nm were linear over a wide concentration range from 100 μg/mL to the detection limits of 10 μg/L for nitrite and 5 μg/L nitrate. Quantitation was carried out by the peak area method. The relative standard deviation for the analysis of nitrite and nitrate was less than 3.0%. This method was applied for the simultaneous determination of nitrite and nitrate in dew, rain, snow and lake water samples collected in southeast Massachusetts. Nitrate was found being present at 4.79–5.99 μg/mL in dew, 1.20–2.63 μg/mL in rain, 0.32–0.60 μg/mL in snow and 0.12–0.23 μg/mL in lake water. Nitrite was only a minor species in dew (0.62–0.83 μg/mL), rain (<0.005–0.14 μg/mL), snow (0.021–0.032 μg/mL) and lake water (0.12–0.16 μg/mL). High levels of nitrite and nitrate observed in dew water droplets may constitute an important source of hydroxyl radicals in the sunny early morning.