Determination of major inorganic anions in rainwater by capillary electrophoresis

A method was optimized and validated for the simultaneous determination of chloride, sulfate and nitrate anions by capillary electrophoresis with indirect UV detection using hydrodynamic sample injection. A good linearity was observed for chloride in a concentration range of 5.0–200 μM, and for sulfate and nitrate in a concentration range of 1.0–200 μM. The relative standard deviations in the peak areas were 7.20%, 3.25% and 4.86% for chloride, sulfate and nitrate, respectively. This method was applied for the determination of sulfate, nitrate and chloride in the rainwater samples collected in Miami, Florida, between 1995 and 1996. An analysis of the rainwater data suggests that chloride found in rainwater most likely originates from marine aerosol, whereas sulfate comes mainly from anthropogenic activities. High levels of nitrate (>30 mM) in rainwater are largely associated with anthropogenic activities and summer thunderstorms in South Florida.