5:15 PM - 6:45 PM
[SVC28-P09] Improvement of CO2 wet analysis method for volcanic gase
Keywords:volcanic gas, CO2, microdiffusion analysis, fixative-free unit
Remote observation techniques such as SO2 measurements using differential optical absorption spectroscopy (Mori et al., 2005) are effective for evaluating the activity of volcanoes with active magmatic gas emissions, while direct sampling of volcanic gases and repeated analysis of chemical compositions such as CO2/H2S ratio and CO2/CH4 ratio is an effective method for detecting minor unrest and precursors of eruptions in volcanoes where hydrothermal systems are developed without significant SO2 emissions (e.g., Ohba et al., 2019a and b). On the other hand, the chemical analysis method for volcanic gases is classical, and improving this method is expected to reduce the time and effort and increase the frequency of chemical observations. In this study, we addressed improving the analytical method for CO2, one of the main components of volcanic gases.
Generally, volcanic fluids such as volcanic gases and volcanic water from crater lakes with high concentrations of CO2 are collected by absorbing them into an alkaline solution (Ozawa, 1968; Giggenbach and Goguel, 1989; Kusakabe et al., 2000). Although there are several wet analysis methods for CO2 in solution, including alkalinity measurement and microdiffusion analysis (e.g., Dixon and Kell, 1998), the latter is often used in recent studies based on direct volcanic gas sampling (Ohba et al., 2019a and b; 2021). In this method, CO2 generated by acidifying a sample solution in a dish-shaped microdiffusion unit is absorbed by a barium hydroxide solution, and the remaining barium hydroxide is titrated with a standard acid to determine the amount of CO2 (Conway, 1950; Saruhashi, 1955; Ozawa, 1968). However, the conventional unit requires the application of fixatives, such as vaseline, to prevent CO2 leakage and contamination of atmospheric CO2. Also, the process of acidifying the sample solution to generate CO2 after sealing the analysis unit requires considerable skill. These were problems to be improved in wet analysis of CO2 in volcanic fluids. Hence, we devised a small resin reaction cell for the sample solution and placed it with a Petri dish in a screw-top glass container to form a microdiffusion analysis unit. Using the newly designed analysis unit, we conducted a CO2 recovery test using 0.3mL of 0.1mol/L sodium carbonate solution as a simulated sample, and we obtained recovery rates of 94-105%. Applying this unit to analyze CO2 in volcanic fluids may reduce the effort and improve the frequency of chemical observations at active volcanoes.
Generally, volcanic fluids such as volcanic gases and volcanic water from crater lakes with high concentrations of CO2 are collected by absorbing them into an alkaline solution (Ozawa, 1968; Giggenbach and Goguel, 1989; Kusakabe et al., 2000). Although there are several wet analysis methods for CO2 in solution, including alkalinity measurement and microdiffusion analysis (e.g., Dixon and Kell, 1998), the latter is often used in recent studies based on direct volcanic gas sampling (Ohba et al., 2019a and b; 2021). In this method, CO2 generated by acidifying a sample solution in a dish-shaped microdiffusion unit is absorbed by a barium hydroxide solution, and the remaining barium hydroxide is titrated with a standard acid to determine the amount of CO2 (Conway, 1950; Saruhashi, 1955; Ozawa, 1968). However, the conventional unit requires the application of fixatives, such as vaseline, to prevent CO2 leakage and contamination of atmospheric CO2. Also, the process of acidifying the sample solution to generate CO2 after sealing the analysis unit requires considerable skill. These were problems to be improved in wet analysis of CO2 in volcanic fluids. Hence, we devised a small resin reaction cell for the sample solution and placed it with a Petri dish in a screw-top glass container to form a microdiffusion analysis unit. Using the newly designed analysis unit, we conducted a CO2 recovery test using 0.3mL of 0.1mol/L sodium carbonate solution as a simulated sample, and we obtained recovery rates of 94-105%. Applying this unit to analyze CO2 in volcanic fluids may reduce the effort and improve the frequency of chemical observations at active volcanoes.