FASTER GAS CHROMATOGRAPHY AND ITS USE IN BREWING. PART 2. – THE DETERMINATION OF HIGH VOLATILE BEER FLAVOURS AFTER HEADSPACE EXTRACTION

Importance of Topic

The rapid determination of volatile sensory-active compounds in beer is crucial for quality control, production optimization and timely decision-making in breweries. Headspace gas chromatography combined with flame ionization detection (HS-GC-FID) forms the backbone of standard methods (EBC, MEBAK, IOB) for monitoring beer flavor and off-flavor compounds. Adopting faster chromatographic approaches addresses growing demands for higher sample throughput without sacrificing analytical performance.

Objectives and Study Overview

This study evaluated the performance of newly available narrow bore capillary columns (20 m × 0.18 mm ID, 0.18 µm film) versus conventional columns (60 m × 0.32 mm ID, 0.25 µm film) for HS-GC-FID quantification of highly volatile beer flavor compounds. Key targets included dimethyl sulfide (DMS) and its precursors, acetaldehyde, lower alcohols and C2–C8 esters. The workbench focused on:

• Optimizing chromatographic conditions via method-translation software.
• Comparing retention, resolution and reproducibility on both column formats.
• Assessing the reduction in analysis time and evaluating real vs. predicted speed gains.

Methodology and Instrumentation

Beer samples were kept at 4 °C and analyzed directly by headspace sampling. Calibration standards (Sigma-Aldrich) included DMS, ethylmethyl sulfide, acetaldehyde, ethyl formate, ethyl acetate, propyl acetate, isobutyl acetate, ethyl butyrate, C3–C5 alcohols and C6–C8 esters. Ultrapure He, H2 and synthetic air (Messer, Czech Republic) supplied carrier/detector gases. Instrumental setup:

• Gas chromatograph: Carlo Erba 5300 Mega Series with split injection.
• Headspace sampler: Dani HSS 3950 loop system.
• Detector: Flame Ionization Detector at 250 °C.
• Columns: J&W Scientific DB-WAX (60 m × 0.32 mm ID, 0.25 µm) vs. DB-WAX (20 m × 0.18 mm ID, 0.18 µm).
• Chromatographic programs calculated through Agilent method translation tools.

Main Results and Discussion

Chromatograms obtained on the narrow bore column demonstrated equivalent separation quality to the conventional column, while analysis times decreased markedly:

• DMS analysis time: reduced from 2.95 min to 1.06 min (real speed gain ~2.8×; calculated ~3.3×).
• Acetaldehyde and volatile esters/alcohols: reduced from 12.3 min to 4.97 min (real speed gain ~2.5×; calculated ~3.0×).

Retention time precision (RSD) was <0.4% on the conventional column and <0.5% on the narrow bore. Peak area repeatability remained <3% (conventional) and <4% (narrow bore). Minor discrepancies between predicted and actual speed gains were attributed to differences in true column lengths after cutting.

Benefits and Practical Applications

The narrow bore 0.18 mm columns offer a balance between fast separations and moderate head pressure (250 kPa) without requiring specialized GC hardware or ultrafast oven heating. Key advantages include:

• Substantial time savings and higher laboratory throughput.
• Maintained chromatographic resolution and reproducibility.
• Seamless implementation on existing GC–FID systems.

Future Trends and Possibilities

Emerging developments will further enhance speed and robustness in beer flavor analysis:

• Integration of advanced cooling systems to minimize oven cycle times.
• Coupling narrow bore GC to mass spectrometry for increased selectivity.
• Automated method-translation and predictive modeling for more rapid method development.
• Application of narrow bore columns to additional matrices such as spirits and soft drinks.

Conclusion

The study demonstrates that 0.18 mm ID capillary columns can be successfully deployed for HS-GC-FID analysis of highly volatile beer flavors, preserving analytical quality while delivering 60–65% faster run times. This approach significantly boosts laboratory efficiency and can be adopted on standard gas chromatographs without major instrument upgrades.

References

James A.T., Martin J.A.P.: Gas-liquid partition chromatography: BIochem J. 50 (1952) 679–690.
Horák T. et al.: Faster gas chromatography and its use in brewing. Part 2. Kvasny Prum. 55 (2009) 268–272.
Jelen H.H. et al.: Solid-phase microextraction vs. static headspace for beer volatiles. J. Agric. Food Chem. 46 (1998) 1469–1473.
Šulák M. et al.: SPME determination of dimethyl sulfide in beer. Kvasny Prum. 54 (2008) 70–74.
Analytica EBC 9.39: Dimethyl sulphide and other volatiles by GC.
MEBAK Band II, 1.1.1: Headspace methods for volatile by GC.
Institute of Brewing Method 9.32: Lower boiling point volatiles by HS-GC.