Beverage Grade Carbon Dioxide Analysis by Gas Chromatography

Importance of the Topic

Beverage-grade carbon dioxide is a critical ingredient in the soft drink and brewing industries. Because CO₂ can be derived from diverse industrial sources such as ammonia synthesis, gasification, fermentation, and petroleum refining, it often carries trace impurities that can impair flavor, safety, and regulatory compliance. Reliable analytical methods are therefore essential to detect, quantify, and confirm a wide range of volatile and non-volatile contaminants at ppm and ppb levels.

Objectives and Study Overview

This study presents a turnkey analytical solution for comprehensive profiling of trace impurities in beverage-grade CO₂. Key objectives include:

• Developing robust gas chromatography methods to separate and quantify hydrocarbons, oxygenates, aromatics, sulfur compounds, permanent gases, and heavy organic residues.
• Achieving low detection limits (down to ppb) and confident analyte identification through combined detector technologies.
• Providing a sample-handling workflow suitable for both gas-phase and pressurized liquid CO₂ inputs.

Methodology and Instrumentation

The analytical system consists of two customized GC platforms from Agilent Technologies:

• GC 1 (Hydrocarbon/Oxygenate/Aromatic Analysis): Dual flame ionization detectors (FID/FID) in series with a mass selective detector (MSD). Flame ionization detectors quantify methane, non-methane hydrocarbons, C₁–C₆ paraffins and olefins (1 ppm), methanol and oxygenates (0.25 ppm mol), and BTEX (0.25 ppm mol). The MSD operates in Selected Ion Monitoring (SIM) mode for ppb-level detection and compound confirmation by spectral fingerprint rather than retention time alone.
• GC 2 (Sulfur and Permanent Gas Analysis): A sulfur chemiluminescence detector (SCD) with cryogenic cooling measures hydrogen sulfide, carbonyl sulfide, sulfur dioxide, mercaptans, disulfides, thiophenes, and total sulfur (0.03–0.1 ppm). A pulsed discharge helium ionization detector (PDHID) quantifies permanent gases (O₂, Ar, N₂, CO, CH₄) at 0.5 ppm mol, with LDLs down to 6.9 ppb for O₂ and 11.6 ppb for Ar. A non-volatile organics concentrator (NVOC) enables extraction of heavy residues (e.g., glycol, pump oils) from pressurized liquid CO₂ into a solvent vial for syringe injection.

Main Results and Discussion

Chromatograms demonstrate sharp, baseline-resolved peaks for hydrocarbons, aromatics, and oxygenates in FID traces, with MSD spectra confirming each analyte signal at low ppb levels. Sulfur compound profiles from SCD exhibit clear separation of mercaptans, disulfides, and thiophenes in a 20 ppm standard blend. PDHID traces resolve O₂ and Ar peaks in permanent gas mixtures, achieving high signal-to-noise ratios and low detection limits. Method reproducibility and calibration linearity were validated across specified concentration ranges.

Benefits and Practical Applications

This dual-GC approach enables beverage producers and quality control laboratories to:

• Ensure CO₂ purity by monitoring a broad spectrum of volatile and non-volatile contaminants.
• Prevent off-flavors and maintain product consistency.
• Meet industry and regulatory specifications for trace impurities.
• Obtain rapid, confirmed identifications with minimized false positives.

Future Trends and Opportunities

Emerging directions in beverage-grade CO₂ analysis include:

• Automation of sample introduction and data processing for higher throughput.
• Integration of real-time monitoring sensors and miniaturized GC systems.
• Advanced chemometric methods for multivariate analysis of complex impurity profiles.
• Coupling GC with high-resolution mass spectrometry for non-targeted screening.

Conclusion

The presented engineered solution, combining dual FID, MSD, SCD, and PDHID detectors with specialized sample handling, provides a comprehensive, sensitive, and confirmatory method for trace impurity analysis in beverage-grade carbon dioxide. This turnkey system supports stringent quality requirements and enhances confidence in CO₂ sourcing and beverage production.