DISPERSIVE LIQUID-LIQUID MICROEXTRACTION (DiLLME) FOR WHISKY FLAVOUR ANALYSIS

Importance of the Topic

Whisky aroma and flavour profiling demands highly sensitive and robust analytical methods to characterise volatile compounds at trace levels, ensuring product quality and authenticity.

Aims and Overview of the Study

This work presents dispersive liquid–liquid microextraction (DiLLME) as an automated, rapid extraction technique for comprehensive flavour analysis of whisky samples, comparing six distinct commercial products.

Methodology and Instrumentation

• Sample Preparation: Six whisky types diluted 1:1 with ultrapure water; duplicates of 7 mL aliquots in high-recovery vials.
• DiLLME Protocol: Addition of 1000 µL dichloromethane/pentane (80:20) and 500 µL isopropanol; 1 min mixing (QuickMix) and 5 min centrifugation at 4500 rpm.
• Injection and Separation: 1 µL splitless injection into GC–MS.
• Instrumentation: GERSTEL MPS with USM and PSM modules, GERSTEL QuickMix, Anatune CF200 centrifuge; Agilent 7250 GC/Q-TOF and Agilent 5977B GC/MS.
• Data Processing: Agilent MassHunter Qualitative and Mass Profiler Professional for deconvolution and Principal Component Analysis.

Main Results and Discussion

DiLLME achieved reproducible total ion chromatograms (RSD ≈6%), revealing distinct volatile profiles among whisky types.

• Key Differences: Enhanced phenolic and cresolic signals in peated (Islay) and Irish samples between 15–17 min retention times.
• PCA Grouping: Clear separation of Single Malt Islay and Irish whiskies from blended Scotches, with subclusters reflecting smoky character.
• Marker Compound: Guaiacol levels highest in Sample C (Islay) and elevated in the ‘black’ blend (Sample F), correlating with smoky notes.

Benefits and Practical Applications

• Minimal Solvent Use: Microlitre volumes reduce cost, waste, and exposure risks.
• Automation and Speed: Extraction completes within analysis cycle time, increasing throughput.
• Versatility: Compatible with single quadrupole or high-resolution Q-TOF detection.
• Environmental and Safety Advantages: Lower solvent handling and disposal requirements.

Future Trends and Applications

• Method Optimization: Larger volume injection or reduced solvent volumes to enhance sensitivity.
• Quantitative Potential: Development of semi-quantitative or fully quantitative protocols.
• Solvent Selection: Alternative extractants to tailor analyte selectivity.
• Broader Matrices: Adaptation to other beverages and food products.
• Advanced Detection: Leveraging accurate-mass data for trace-level compound identification.

Conclusion

Dispersive liquid–liquid microextraction (DiLLME) provides a fast, automatable, and environmentally friendly approach for reliable whisky flavour profiling, matching traditional extraction techniques while offering cost and safety benefits.

References

1. Comparison of Extraction Techniques for Volatiles in a Selection of Spirits and Liqueurs; Kathy Ridgway, Anatune Ltd., AS180, 2019.
2. The Development of the Multi-Volatile Method (MVM) in the Whisky Matrix; Maïlie Saint-Hilaire & Kathy Ridgway, Anatune Ltd., Technical Note AS148, 2015.
3. Determining Phenolic Compounds in Whisky using Direct Large Volume Injection and Stir Bar Sorptive Extraction; Yunyun Nie & Eike Kleine-Benne, Gerstel GmbH & Co. KG, Application Note 2012-02.
4. Using Three Types of Twister Phases for Stir Bar Sorptive Extraction of Whisky, Wine and Fruit Juice; Yunyun Nie & Eike Kleine-Benne, Gerstel GmbH & Co. KG, Application Note 2011-03.