Use of capillary electrophoresis to monitor concentrations of organic acids in snow and rain water

The concentrations of six organic acids present in snow and rain water were determined during the spring of 1992, in order to test the possibilities of capillary electrophoresis for measurements in the environment. The sampling sites were located in the French Alps. Fourteen samples were taken. This method allows routine analysis. The following acids, normally found in snow and rain waters, were satisfactorily separated after 5 min: formic, acetic, propionic, butyric, oxalic and benzoic, with concentrations of the order of 10−6 M. The sample size was very small since a 100-μl aliquot is sufficient to perform an analysis without previous treatment or preliminary concentration. For these three reasons — time, sensitivity and sample amount — capillary electrophoresis is suitable for measurements in the environment. Short sampling times can be used, for example, in order to follow rain events. Monitoring organic acids in hydrometeors collected at high altitude show that their concentrations are fairly constant for the various individual rain or snow samples but are different for rain and snow samples. The total concentrations observed for the five acids detected (all organic acids except oxalic) ranged from 5 to 10 μM for rain water and 0.5 to 5 μM for snow. The pofile established from the relative abundance of the acids diffeers from snow to rain and depends on the season, which confirms that formic acid is a biogenic tracer and acetic acid is an anthropic tracer. Furthermore, we show, for the first time, that butyric acid is a good tracer of bacterial activity.