Determination of Volcanic Gases as Anions in Caustic Solutions Using AutoNeutralization, Automated Dilutions, and a Reagent-Free Ion Chromatography System

Significance of the Topic

Volcanic gas emissions strongly influence local water quality, human health, and atmospheric chemistry. Accurate quantification of gas components—converted to their anionic forms in alkaline solutions—is vital for monitoring volcanic activity, predicting eruptions, and assessing environmental impact.

Objectives and Overview of the Study

This work presents an analytical strategy to determine a broad range of volcanic gas–derived anions (carbonate, sulfate, halides, thiosulfate, thiocyanate, phosphate, and arsenate) in highly caustic condensate matrices. Key goals include:

• Overcoming the challenges of extremely disparate analyte concentrations (µg/L to 10^5 mg/L) and strong hydroxide backgrounds.
• Preserving labile carbonate levels despite degassing or CO₂ absorption.
• Integrating sample neutralization, concentration, dilution, and ion chromatography on a single reagent-free RFIC system.

Methodology and Sample Preparation

Samples of volcanic gas condensates were collected in 6 M NaOH to trap gas anions. The analytical procedure comprised:

1. Park & AutoNeutralization: electrolytic removal of excess hydroxide in the ASRN II neutralizer, converting anions to acid forms.
2. Concentration: trapping neutralized anions on a UTAC-XLP1 concentrator column.
3. Automated dilutions: AS Autosampler pipet-and-mix commands delivered freshly degassed deionized water from sealed glass vials to prepare 10× and 1000× dilutions without atmospheric CO₂ contamination.
4. Separation and detection: reagent-free eluent generation (EGC II KOH), IonPac AS19/AG19 columns, suppressed conductivity detection, and optional 4 mm carbonate removal device for low-range determinations.

Used Instrumentation

• Dionex ICS-3000 RFIC system: dual pumps, dual conductivity detectors, DC module, EG module, Automation Manager with 10-port valve.
• Anion Self-Regenerating Neutralizer ASRN II (external water mode).
• IonPac AG19/AS19 analytical and guard columns (4 mm).
• IonPac UTAC-XLP1 concentrator and CR-ATC trap columns.
• EluGen II potassium hydroxide cartridge and suppressor ASRS ULTRA II.
• AS Autosampler with temperature control, 500 µL and 5 mL syringes.

Main Results and Discussion

Optimization via Virtual Column simulation and experimental trials established a 14 mM KOH isocratic eluent for baseline resolution of carbonate (5–60 mg/L) and sulfate (0.5–6 mg/L) with quadratic and linear calibration, respectively (r²>0.99). Method detection limits for trace anions (iodide, thiosulfate, thiocyanate, arsenate) ranged from 2.9 to 13.7 µg/L. Automated dilutions reduced carbonate interference and preserved low-level analytes. Application to volcanic condensates yielded:

• Carbonate: 45 000–77 000 mg/L; sulfate: 3 900–5 200 mg/L (1000× dilutions).
• Trace anions (fluoride, chloride, bromide, iodide, thiosulfate, thiocyanate, phosphate, arsenate) quantified in 10× dilutions with recoveries of 89–112%.

Benefits and Practical Applications of the Method

• Single-system analysis eliminates configuration changes, reducing hands-on time and error risk.
• Reagent-free eluent generation and self-regenerating suppressors lower consumable costs and waste.
• Automated dilutions preserve carbonate integrity and extend dynamic range, enabling simultaneous trace and high-level determinations.
• Rapid, selective, and reproducible analysis supports real-time volcanic monitoring and environmental assessment.

Future Trends and Applications

Potential developments include:

• Integration with field-deployable RFIC modules for on-site volcanic gas monitoring.
• Extension to additional redox-sensitive anions or organic gas tracers via dual detection (conductivity and mass spectrometry).
• Coupling with real-time data platforms and predictive models for eruption forecasting.
• Miniaturized autosampler and neutralizer designs for remote sampling or drone-based monitoring.

Conclusion

The combination of AutoNeutralization pretreatment, automated dilutions, and reagent-free ion chromatography yields a powerful, flexible approach for analyzing volcanic gas condensate anions across seven orders of magnitude. The methodology addresses carbonate stability, minimizes manual handling, and delivers high accuracy for both major and trace analytes, offering significant advantages for volcanological research and environmental monitoring.

References

1. Griggs J. et al. U.S. Geological Survey Volcano Hazards Program, 2000.
2. Hinkle S.; Polette D. Water-Resources Investigations Report 98-4205, 1999.
3. Rogie J. U.S. Geological Survey Volcano Hazards Program, 2001.
4. Caliro S. et al. IAVCEI, 2005.
5. Christenson B.W.; White S.P. IAVCEI, 2005.
6. Faber E. et al. IAVCEI, 2005.
7. Fehn U.; Snyder G.T. Soc. Econ. Geol. Spec. Publ. 10, 2003.
8. Polesello S. et al. J. Chromatogr. A 1118, 56–61, 2006.
9. Dionex Application Note 93, 2007.
10. Dionex ICS-3000 Manuals, 2005.
11. Dionex Product Manuals for AS19/AG19, UTAC-XLP1, ASRN II, ASRS ULTRA II, CRD, 2002–2005.