Possibilities of Utilization of Modern Sample Preparation Methods for Gas Chromatographic Analysis of Beverages and especially Beer. Part II. – Stir Bar Sorptive Extraction

Significance of the Topic

Stir bar sorptive extraction (SBSE) addresses key trends in analytical chemistry by enabling simplified, miniaturized sample preparation with minimal solvent and sample consumption. This technique concentrates volatile and semi-volatile organic compounds from aqueous matrices, reducing costs and time while improving sensitivity and selectivity in beverage analysis, particularly for beer quality control.

Objectives and Study Overview

The reviewed article aims to summarize the principles, optimization parameters, recent phase developments and applications of SBSE for gas chromatographic analysis of beverages—focusing on beer. It discusses critical factors influencing extraction efficiency, emerging sorbent materials, and practical uses in soft drinks, wine, sake, spirits and brewing analytics.

Methodology and Instrumentation

SBSE employs a magnetic stirring bar coated with polydimethylsiloxane (PDMS) enclosed in a glass jacket. Key extraction parameters include:

• Extraction time (30–240 min), stirring speed and bar dimensions
• Sample pH and ionic strength to favor neutral analyte forms
• Temperature to balance partition coefficient and diffusion rate
• Use of organic modifiers (≈10 vol %) to reduce wall adsorption of hydrophobic analytes
• Derivatization of polar compounds to improve sorption

Desorption is achieved by thermal desorption directly into a GC–MS system or by solvent back-extraction (100–200 µL) for GC-FID, GC-ECD or LC-based detectors.

Used Instrumentation

• Gerstel Twister stir bar sorptive extraction device
• Thermal desorption unit coupled to GC–MS and GC–TOFMS
• Capillary gas chromatography with flame ionization (FID) or electron capture detection (ECD)
• High-pressure liquid chromatography (HPLC) for back-extracted samples

Main Findings and Discussion

• Extraction efficiency correlates with the analyte’s octanol–water partition coefficient (Ko/w) and phase ratio (β). SBSE’s larger PDMS volume (25–125 µL) outperforms SPME for compounds with Ko/w > 500, boosting sensitivity 50–250×.
• Phase developments—dual-phase bars combining PDMS with carbon adsorbents, porous sol–gel coatings, alkyl-diol silica, polyurethane foams and tailored copolymers—extend SBSE to polar analytes and heavy metals.
• SBSE applications in beverages include determination of preservatives (benzoic acid), flavor compounds in wines, sake, whisky, juices, coffee and off-flavor sulfur or carbonyl compounds in beer.
• Back-extraction combined with GC-FID/ECD or HPLC enables quantitative analysis of esters, medium-chain fatty acids, vicinal diketones and bitter acids in beer.

Benefits and Practical Applications

SBSE offers a single-step extraction/concentration protocol that reduces solvent use and sample handling. Its high sensitivity and wide dynamic range suit QA/QC, sensory profiling and trace-level monitoring of flavor, aroma and off-flavor compounds in the beverage industry.

Future Trends and Potential Applications

• Development of novel multi-functional sorbent phases to target highly polar compounds and specific analyte classes.
• Integration with automated thermal desorption systems and hyphenated techniques (GC×GC, LC–MS) for comprehensive volatile profiling.
• Expansion into on-site monitoring and remote sampling using portable SBSE devices.
• Application in emerging beverage matrices (functional drinks, plant-based alternatives) and real-time quality control.

Conclusion

Stir bar sorptive extraction has established itself as a powerful microextraction tool for gas chromatographic analysis of beverages, especially beer. Its simplicity, high phase ratio and low solvent consumption deliver superior sensitivity compared with classical techniques. Continued phase innovation and method integration promise broader applicability across the beverage sector and beyond.

Reference

Horák T., Čulík J., Jurková M., Čejka P., Kellner V., Dvořák J., Hašková D. (2010) Possibilities of utilization of modern sample preparation methods for gas chromatographic analysis of beverages and especially beer. Part II – Stir Bar Sorptive Extraction. Kvasny Prum 56(10):390–395.