Analysis of individual raindrops by capillary zone electrophoresis

A new technique for the analysis of individual raindrops by CZE was developed. This system is at present the only method which facilitates a simultaneous determination of concentration of trace elements in individual raindrops and the size of individual raindrops. The use of this method allows in future works the determination of the concentration of trace compounds as a function of the radius of individual raindrops. This paper presents the development of an injection technique and the development of a method to store and to handle small raindrops (i.e., volumes in the nanoliter range). The storing method makes it possible to handle drops in the nanoliter range without any contamination. The injection occurred using a new developed microinjection system which allows a direct introduction of individual raindrops into the separation capillary. Furthermore different methods to determine the volume of single raindrops were investigated. To employ this new system for the analysis of real samples calibration graphs for inorganic cations were made. The absolute limits of detection for the cations NH4+ K+, Na+, Ca2+, Mg2+ and Zn2+ ranged from 40-80 fmol using indirect UV detection. The applicability of the new developed method to real rain samples was demonstrated.