Identification of Chemical Species of Silica in Natural Hot Water using Fast Atom‐Bombartment Mass Spectrometry

Abstract

The identification of silica species dissolved in natural hot water was performed. Three typical hot spring waters, which were collected from Hakone Hot Spring (Kowakudani), Nakafusa Hot Spring, and Tateyama Hot Spring Shin‐yu, were examined. Generally, it is known that, in Nakafusa Hot Spring and Tateyama Hot Spring shin‐yu, oolite opal (siliceous oolite) and massive opal are sintered. These hot spring waters were analyzed with ICP‐AES, ICP‐MS, colorimetry, ion chromatography, and FAB‐MS (fast atom‐bombardment mass spectrometry). Nakafusa Hot Spring water is characterized by the high pH indicates that the sinter of the Nakafusa Hot Spring water contains a high concentration of arsenic while, in Tateyama Hot Spring Shin‐yu, arsenic ions were contained at high concentrations from the water. The concentration of silica in Nakafusa Hot Spring and Tateyama Hot Spring Shin‐yu hot spring waters was measured by colorimetry and ICP‐AES. The concentration of silica in those waters, measured by ICP‐AES, is higher than that measured by colorimetry but, in the Hakone hot spring water, the concentrations of silica, as measured by the ICP‐AES and colorimetry were the same. This indicates that large species of silica, which could not be detected by colorimetry, were present in Nakafusa Hot Spring and Tateyama Hot Spring Shin‐yu. The silica species was identified to have several chemical forms and all of the species are replaced with sodium ions. It was notable that the peak intensity ratios of 329/311 and 195/173 in Nakafusa Hot Spring and Tateyama Hot Spring Shin‐yu waters were higher than those obtained by experiments employing the simple system of sodium chloride (NaCl) solution with silica and the Hakone Hot Spring water. Therefore, the silica species in both spring waters hydrated after the precipitation of silica as particles.