降水中のアミノ酸濃度の定量

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Ice nucleation plays an important role in the precipitation process of supercooled water in the air. Many studies have shown that various amino acids have an effective ability for nucleation of supercooled water, but there are few studies in which amino acids were measured in rain water. To constrain better estimate of amino acids in rain water, we checked preservation and analytical method of amino acids. As the result of our examinations, we concluded that rain water is to be collected in a 50ml-polystyrene centrifuge tube and to be kept frozen in the tube until analysis. Analysis of amino acids is required to do as soon as possible by a high performance liquid chromatography (HPLC) to avoid significant decrease of amino acids which we confirmed during a preservation for 24 hours. Measurement of amino acids by a spectrofluorometer is not adequate, because high concentration of NH^+_4 causes overestimation of amino acids. NH^+_4 interfere in determination of α-aminob utyric acid and methionine, but it is removed by evaporation with a vacuum oven in the presence of 1 M borate-citrate buffer (pH 11). Rain water samples were collected at the Mt. Norikura, Mizugatsuka Park at the Mt. Fuji and Shigaraki. Concentration 'of total free amino acids ranged from 219 to 3090 nmol/l, showing a large variability depending on the study area : Shigaraki samples marked one order of magnitude higher than that of the Mt. Norikura and Mizugatsuka. On the other hand, composition of amino acids was not markedly different among the three area. 11 to 47% of amino acids were comprised by glycine, serine and alanine. Our findings of the lower concentrations and major composition of amino acids are consistent with the previous results of marine rains, but the higher concentration implies the possibily of the effect of air pollution and/or Chinese loess on amino acids in rain water at Shigaraki.

降水中のアミノ酸濃度の定量

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