Verlag des Forschungszentrums Jülich
JUEL-3709
Baade, Andre
Entwicklung zur Spurenanalytik in Mikrovolumina und deren Anwendung bei der Charakterisierung von Niederschalgsereignissen und einzelnen Regentropfen
161 S., 1999
Rain is the predominant route for the atmospheric deposition of environmentally relevant
compounds. For a better understanding of wash-out effects of metals such as Pb, Cu, and Cd
it is necessary to examine individual rain events. The main focus of the present work was the
determination of trace heavy metals in individual rain drops and rain drop fractions for a
detailed investigation of different precipitation events such as cloudburst, drizzle, hail and
snow. Moreover, the wash-out rate during the first minutes of rain events and the comparison
of a typical urban location (Essen) with a rural area (Jülich) were of special interest.
The method development included a sampling procedure for individual and size-classified
rain drops by using liquid nitrogen. Furthermore, an approach for the determination of trace
heavy metals in microvolumes was introduced. The measurements have been perrormed by
using voltarnmetric techniques based on microelectrodes and ETV-ICP-MS. The possibilities
and limitations of these approaches are shown. The stripping voltarnmetry required the
development of specially designed measuring cells and single microelectrodes or microelectrode
arrays. By such procedures determinations of Pb, Cu, Cd and Zn were carried out in
microliters of rain water (2-100 µl) and absolute detection limits in the lower picogram range
were achieved. Additionally a thin-layer flow cell in combination with microelectrode arrays
was developed and the influence of a piezo actuator on the accumulation efficiency of the
analyte on the electrode sufface was discussed. By the application of these analytical methods
on precipitation samples, specific concentration maxima in defined drop size fractions were
found for Pb, Cu and Cd at both sampling sites (Essen, Jülich). For lead an increase of the
metal concentration in drop volumes of 4 and 8 µl was detected. All rain events showed a
strong decrease in metal concentrations after 3 to 10 minutes. In addition to metal
determinations the pR in rain drop fractions was analysed with ion-sensitive field effect
transistors (ISFET). Also the input of major rain water constituents at both sampling areas
was characterized by using ion chromatography and ETV-ICP-MS. Generally large
concentration variations of all measured compounds between weekly collected rain samples were
observed, but the average concentrations over the year were similar at both sampling areas.
Obviously, the influence from local emission sources was low.
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