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[SVC33-07] Uncertainty in Determination of Sulfate in Crater Lake Water by Ion Chromatography
Keywords:hydrothermal fluids, Ion Chromatography, sulfur species, crater lake
Kusatsu-Shirane Volcano, located in Gunma Prefecture, is an active volcano, which has an active crater lake called Yugama. Many researchers are paying attention to changes in the chemical composition of Yugama water to evaluate the volcanic activity of the volcano.
By observing the chemical composition of active crater lakes like Yugama, indicators such as SO42-/Cl- mole ratio can be measured to evaluate the volcanic activity [1]. Additionally, the SO42-/Cl- mole ratio of volcanic hot spring changes with activation of volcanic activity and may reflect the state of volcanic activity [2,3]. Thus, the SO42-/Cl- mole ratio of geothermal fluids is the key indicator for monitoring volcanic activity. Needless to say, to determine the SO42-/Cl- mole ratio correctly, accurate and precise analytical methods of SO42- and Cl- are required.
Ion Chromatography (IC) is a common method used for quantitative analysis of anions. However, the IC's analytical accuracy may be significantly reduced depending on the sample's characteristics. In this study, we will discuss the difficulties in determination of anions, especially sulfate, in geothermal fluids by using IC. The IC analysis for anions in the Yugama sample in our laboratory gave confusing results. The higher the dilution ratio of the sample when it is measured, the higher the determined concentration of SO42- is presented in the IC analysis. On the other hand, IC has no such abnormality in the Cl- determination.
The water samples of Yugama have several characteristics. Firstly, it shows high acidity with a pH value of around 1. Secondly, it is high salinity the water samples containing thousands of mg/L Cl- and SO42- and hundreds of mg/L Al, Ca and Fe. There are polythionate (SnO62-) besides SO42- as dissolved sulfur species in Yugama water [4].
Considering the characteristics of Yugama water, we conducted laboratory experiments to clarify the factors that affect the results of SO42- determination by IC. We prepared a series of Cl--SO42- solutions simulated the Yugama water. Then, by changing the several parameters in the solutions, such as Al3+ and other metal cations concentration and pH, investigate the factors that affect the determined SO42- concentration by IC. The IC system used in this study is Metrohm 883 Basic IC plus (Metrosep A Supp 4-250/4.0 column, electrical conductivity detector) with 1.8 mM Na2CO3-1.7 mM NaHCO3 eluent.
Based on the experimental results, it was suggested that the high concentration of Al3+ and low pH in the analytical sample interfere with the measurement results of SO42- by IC depending on the analytical conditions. When applying IC to the determination of anions in some crater lake water and hot spring water with high salinity, it is needed that the appropriate verification of analytical accuracy in advance.
Y. Taran, E. Kalacheva, Acid sulfate-chloride volcanic waters; Formation and potential for monitoring of volcanic activity, Journal of Volcanology and Geothermal Research, Volume 405, 107036, ISSN 0377-0273, 2020. Takafumi Furukawa, Akira Ueda. Tamagawa hyper-acidic hot spring and phreatic eruptions at Mt. Akita-Yakeyama: Part 1. The isotopic and chemical characteristics of the hot spring water. Journal of Volcanology and Geothermal Research, Volume 412, 2021. Akira Ueda, Toshiaki Tanaka, Minoru Kusakabe, Takafumi Furukawa. Tamagawa hyper-acidic hot spring and phreatic eruptions at Mt. Akita-Yakeyama Volcano: Part 2. Secular variations of SO4/Cl ratios and their relationship to the phreatic eruptions. Journal of Volcanology and Geothermal Research, Volume 414, 2021. Bokuichiro Takano. Correlation of Volcanic Activity with Sulfur Oxyanion Speciation in a Crater Lake. Science, Vol.235, 4796, p1633-1635, 1987.
By observing the chemical composition of active crater lakes like Yugama, indicators such as SO42-/Cl- mole ratio can be measured to evaluate the volcanic activity [1]. Additionally, the SO42-/Cl- mole ratio of volcanic hot spring changes with activation of volcanic activity and may reflect the state of volcanic activity [2,3]. Thus, the SO42-/Cl- mole ratio of geothermal fluids is the key indicator for monitoring volcanic activity. Needless to say, to determine the SO42-/Cl- mole ratio correctly, accurate and precise analytical methods of SO42- and Cl- are required.
Ion Chromatography (IC) is a common method used for quantitative analysis of anions. However, the IC's analytical accuracy may be significantly reduced depending on the sample's characteristics. In this study, we will discuss the difficulties in determination of anions, especially sulfate, in geothermal fluids by using IC. The IC analysis for anions in the Yugama sample in our laboratory gave confusing results. The higher the dilution ratio of the sample when it is measured, the higher the determined concentration of SO42- is presented in the IC analysis. On the other hand, IC has no such abnormality in the Cl- determination.
The water samples of Yugama have several characteristics. Firstly, it shows high acidity with a pH value of around 1. Secondly, it is high salinity the water samples containing thousands of mg/L Cl- and SO42- and hundreds of mg/L Al, Ca and Fe. There are polythionate (SnO62-) besides SO42- as dissolved sulfur species in Yugama water [4].
Considering the characteristics of Yugama water, we conducted laboratory experiments to clarify the factors that affect the results of SO42- determination by IC. We prepared a series of Cl--SO42- solutions simulated the Yugama water. Then, by changing the several parameters in the solutions, such as Al3+ and other metal cations concentration and pH, investigate the factors that affect the determined SO42- concentration by IC. The IC system used in this study is Metrohm 883 Basic IC plus (Metrosep A Supp 4-250/4.0 column, electrical conductivity detector) with 1.8 mM Na2CO3-1.7 mM NaHCO3 eluent.
Based on the experimental results, it was suggested that the high concentration of Al3+ and low pH in the analytical sample interfere with the measurement results of SO42- by IC depending on the analytical conditions. When applying IC to the determination of anions in some crater lake water and hot spring water with high salinity, it is needed that the appropriate verification of analytical accuracy in advance.
Y. Taran, E. Kalacheva, Acid sulfate-chloride volcanic waters; Formation and potential for monitoring of volcanic activity, Journal of Volcanology and Geothermal Research, Volume 405, 107036, ISSN 0377-0273, 2020. Takafumi Furukawa, Akira Ueda. Tamagawa hyper-acidic hot spring and phreatic eruptions at Mt. Akita-Yakeyama: Part 1. The isotopic and chemical characteristics of the hot spring water. Journal of Volcanology and Geothermal Research, Volume 412, 2021. Akira Ueda, Toshiaki Tanaka, Minoru Kusakabe, Takafumi Furukawa. Tamagawa hyper-acidic hot spring and phreatic eruptions at Mt. Akita-Yakeyama Volcano: Part 2. Secular variations of SO4/Cl ratios and their relationship to the phreatic eruptions. Journal of Volcanology and Geothermal Research, Volume 414, 2021. Bokuichiro Takano. Correlation of Volcanic Activity with Sulfur Oxyanion Speciation in a Crater Lake. Science, Vol.235, 4796, p1633-1635, 1987.