Analysis of Dissolved Argon, Oxygen, and Nitrogen in Solutions

Importance of the Topic

Measurement of dissolved rare and major gases such as argon, oxygen, and nitrogen at trace levels is critical for controlling the physical and chemical performance of solutions in fields ranging from pharmaceutical manufacturing to environmental monitoring. Reliable quantitation of these gases informs solution stability, reactivity, and quality control.

Objectives and Study Overview

This study demonstrates a straightforward method for direct analysis of dissolved Ar, O₂, and N₂ in aqueous and organic media using a barrier discharge ionization detector (BID) on the Shimadzu Nexis GC-2030 with an autoinjector. The key goals were to develop calibration curves using air as a surrogate standard gas, achieve linear quantitation at trace levels, and assess repeatability in various solvents.

Methodology and Instrumentation

• Gas Chromatograph: Shimadzu Nexis GC-2030 with AOC-30i autoinjector.
• Column: SH-Rt™-Msieve 5A (30 m × 0.32 mm I.D., 20 μm) with 2.5 m particle trap; constant temperature 35 °C.
• Carrier Gas: Helium at linear velocity of 50 cm/s; purge gas 20 mL/min.
• Injection: Split mode (1:25) at 250 °C; 0.5 μL plunger-in-needle syringe.
• Detector: BID-2030 at 300 °C with 50 mL/min detector gas and 50 ms filter time constant.
• Calibration: Air injected in volumes from 0.05 to 0.5 μL; gas fractions assumed Ar 0.0934%, O₂ 20.9%, N₂ 78.1%.

Results and Discussion

• Calibration curves for Ar, O₂, and N₂ showed excellent linearity (R² > 0.999) across the tested injection volumes.
• Quantitative analysis in hexane, toluene, ethanol, acetone, and water revealed good repeatability (<5% RSD) for organic solvents, while water samples exhibited poor repeatability (>10% RSD) due to low gas solubility.
• Continuous injection of acetone led to N₂ peak shape degradation, which was mitigated by baking the column and performing periodic air injections for re-equilibration.
• O₂ response decreased after high-temperature conditioning but could be restored by injecting larger air volumes prior to measurement.

Benefits and Practical Applications

This automated method allows low-cost, reliable quantitation of dissolved inert and reactive gases without specialized calibration gases, streamlining quality control in laboratories handling both aqueous and organic solutions.

Future Trends and Applications

Future enhancements may include expanded detection of additional gases such as CO₂ and H₂, integration with robotics for fully automated sample handling, and real-time data analytics for process monitoring in pharmaceutical and environmental applications.

Conclusion

The Shimadzu Nexis GC-2030 with BID and autoinjector provides a robust platform for trace quantitation of dissolved Ar, O₂, and N₂ across a variety of solvents. Employing air as a surrogate calibration standard delivers linear, repeatable results for organic media, although water analysis remains challenging. Regular conditioning and air re-injections ensure consistent detector performance.

References

1. Application News GC Nexis™ GC-2030 Analysis of Dissolved Argon, Oxygen, and Nitrogen in Solutions, Shimadzu Corporation, First Edition: Jul. 2021