Analytical Sciences

Quantitative Analytical Method for Single Rain Droplets via Crystal Formation in Photocrosslinking Polymer Gel

Ben NANZAI,* Yoshiaki GOTO,** Yoshihito ISHIDA,*** and Manabu IGAWA**

*Department of Materials and Life Science, Faculty of Science and Technology, Shizuoka Institute of Science and Technology, 2200-2 Toyosawa, Fukuroi, Shizuoka 437-8555, Japan
**Department of Material and Life Chemistry, Faculty of Engineering, Kanagawa University, 3-27-1 Rokkakubashi, Kanagawa, Yokohama 221-8686, Japan
***Science Laboratory, Teikyo University of Science, 2525 Yatsuzawa, Uenohara, Yamanashi 409-0193, Japan

Ion composition contained in individual rain droplets provides important information to investigate the chemistry in rain and clouds, but general rain sampling equipment temporally and spatially averages the information. Determination of the SO₄²⁻ concentration in an individual rain droplet was achieved by precipitate production in synthesized acrylamide polymer gel. Concentration of the target ion was calculated from the droplet print diameter and precipitation area measured from digital microscope images. We investigated the effects of the interior electrolyte concentration in the polyacrylamide gel and UV irradiation time on the physical properties of the gel and precipitate formation. The precipitated components were identified by scanning electron microscopy with energy dispersive X-ray analysis. We also clarified the effects of coexisting ions on the reaction between the interior and exterior electrolytes. For actual rainwater, the SO₄²⁻ concentration estimated by this method was in agreement with the results obtained by ion chromatography.

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