Simultaneous Total and Speciation Analysis of Volatile Arsenic Compounds in Gas and Liquefied Gas Samples using GC-ICP-MS

Importance of the Topic

Monitoring arsenic species and total arsenic in gas and liquefied gas matrices is critical for industrial safety, environmental protection, and product quality. Volatile arsenic compounds such as arsine can poison polymerization catalysts, degrade polymer properties, and pose severe health risks due to their high toxicity. A robust analytical approach that delivers both speciation and total elemental information in a single measurement is essential for gas producers, petrochemical plants, and quality control laboratories.

Objectives and Study Overview

The study describes a novel gas chromatography inductively coupled plasma mass spectrometry method configured to perform simultaneous speciation and total analysis of volatile arsenic compounds. The method aims to determine total elemental arsenic alongside individual species such as arsine, and demonstrate extension of the approach to other elements like mercury. Application to synthetic butane, real propylene samples, and calibration standards supports method validation and real sample assessment.

Methodology and Used Instrumentation

A dual-injection GC-ICP-MS setup was established using an Agilent 7890B GC with two gas sampling valves and a J W GS-GasPro capillary column. A dedicated inert transfer line bypasses the column for total elemental analysis. Both flows merge at a heated interface before entering the Agilent 7900 ICP-MS. Online dilution is achieved with a GasMix Aiolos II dilutor and an Alytech vaporizer chamber for liquefied samples. Key parameters include a 1:6 split ratio, column flow 3 mL per minute, transfer line flow 5 mL per minute, oven ramp from 40 to 250 degrees in five minutes, RF power 1600 W, and helium cell gas. Nitrogen addition to the argon dilution gas enhances arsenic sensitivity.

Main Results and Discussion

Calibration with arsine in nitrogen over 0.2 to 68 ppb showed excellent linearity (r2 of 0.9996 for total arsenic and 0.998 for speciation). Detection limits were 2 ppt for total arsenic and 12 ppt for arsine. Recovery experiments yielded 89 percent of total arsenic observed as arsine, confirming exclusive presence of that species. Analysis of a synthetic butane sample doped with noncertified arsine delivered 92 ppb total and 95 ppb speciation, agreeing with external laboratory results. Real propylene samples demonstrated phase partitioning, with 54 ppb total in the gas phase and 34 ppb in the liquid phase. Mercury coanalysis illustrated multi-element capability, although peak tailing suggested surface adsorption that may be mitigated by further optimization.

Benefits and Practical Applications

• Simultaneous quantitation of total element and individual volatile species in a single 5-minute injection
• No preconcentration step required due to low ppt detection limits
• Multi-element analysis capability for any ICP-detectable impurity
• Online dilution and vaporization streamline analysis of both gas and liquefied samples
• Fast throughput supports industrial acceptance and rejection decisions for gas stocks

Future Trends and Potential Applications

Extension of this approach may target additional trace elements in complex gas mixtures including hydrogen sulfide or volatile organometallics. Integration with automated sample handling could enable real time process monitoring. Advances in micro GC columns and interface miniaturization may reduce gas consumption and improve field deployability. Coupling with machine learning for pattern recognition may speed contaminant screening in biogas, natural gas, and specialty gas supplies.

Conclusion

The introduced GC-ICP-MS configuration offers a powerful, rapid, and sensitive platform for simultaneous total and speciation analysis of volatile arsenic and other trace elements. With low detection limits, reliable recovery, and multi-element capability, the method is well suited for routine quality control and research in gas and petrochemical industries.

References

1. Freije-Carrelo L, Moldovan M, García Alonso JI, Diep Thanh V T, Ruiz Encinar J. Instrumental Setup for Simultaneous Total and Speciation Analysis of Volatile Arsenic Compounds in Gas and Liquefied Gas Samples. Anal Chem. 2017;89(11):5719–5724.
2. Yang S, Chen Y. Determination of Arsine in Ethylene and Propylene by GC-ICP-MS. Handbook of Hyphenated ICP-MS Applications. 2nd Ed. 2015:75–76.