Direct-Injection GC×GC-HRMS Profiles Whiskies

High-end food and drink products like olive oil, wine, and whiskey are often targets for fraud. The good news is that these products are chemically complex, which means there are plenty of potential clues that can help detect when something's been tampered with or faked. The bad news is that picking up on these clues requires powerful, thorough testing methods along with careful sample preparation. One technique that can both look for specific known markers and scan broadly for anything unusual is comprehensive two-dimensional gas chromatography coupled to high-resolution mass spectrometry (GC×GC-HRMS). However, like most chromatography-based methods, this technique usually requires a lot of sample prep work to remove unwanted material, and that prep process runs the risk of accidentally stripping out useful information along the way. To get around this problem, researchers developed a new version of the technique that skips much of that prep work, injecting whiskey samples directly, to get a more complete quality profile. A paper based on this research was published in the Journal of Separation Science.¹

What Analytical Methods Are Used to Verify Whiskey Authenticity and Quality, and What Challenges Do Sample Preparation Steps Pose?

Scientists have proposed a wide variety of testing methods to verify whiskey's authenticity, tell different whiskies apart, and check their quality. These include techniques like Raman spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, Fourier-transform infrared spectroscopy (FT-IR), and gas- and liquid chromatography (GC and LC), either or not hyphenated to mass spectrometry (MS).² Interestingly, some spectroscopy-based methods can analyze whiskey right through an unopened bottle, without needing to open it at all, which makes them especially useful for verifying that a sealed bottle is authentic.³Unfortunately, any process involved in collecting and preparing samples for testing runs the risk of losing or reducing certain compounds, compounds that could actually hold important clues about the whiskey's quality and authenticity.⁴“While minimal sample preparation is generally preferred to preserve the integrity of the sample,’ write the authors of the paper,¹ “sufficient preparatory steps must be employed to ensure robust and reproducible analyses using the selected chromatographic method. Obviously, the sample preparation method selected should ideally be automated, fast, and green, while maintaining a high compound coverage and sensitivity. Novel sample preparation techniques—most notably those that can be automated—can reduce the time and labor substantially.”

How Well Did the Direct-Injection GC×GC-HRMS Method Perform When Applied to a Large Set of Whiskey Samples?

For this study, the researchers fine-tuned several settings for injecting the whiskey samples directly, since testing a large batch of samples this way required extra care to make sure the data stayed accurate and reliable. For most compounds, there was very little carryover between samples, less than 1.5%. However, certain compound types were a bit trickier, with carryover reaching up to about 7% for long-chain fatty acids, 11% for sugar-related compounds, and 18% for lignin-related compounds. Even so, the method was sensitive enough to pick up on a wide range of compounds useful for assessing quality.¹

The team tested this method on 59 different whiskies, running some samples multiple times to check how consistent and reliable the results were over time. Afterward, they used statistical analysis to confirm that the data collected was solid and trustworthy. By applying techniques that help identify patterns and group similar samples together, the researchers were able to pull out useful insights, including clues about how the whiskies were made and even information related to award or quality rankings.¹

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References

1. van 't Veer, B. R.; Affourtit, S.; Janssen, H. G. Direct Liquid Injection in Comprehensive Two-Dimensional Gas Chromatography Hyphenated to Quadrupole Time-of-Flight Mass Spectrometry Quality Profiling of Commercial Whiskies. J Sep Sci. 2026, 49 (7), e70490. DOI: 10.1002/jssc.70490
2. Okolo, C. A.; Kilcawley, K. N.; O'Connor, C. Recent Advances in Whiskey Analysis for Authentication, Discrimination, and Quality Control. Compr Rev Food Sci Food Saf. 2023, 22 (6), 4957-4992. DOI: 10.1111/1541-4337.13249
3. Ellis, D. I.; Muhamadali, H.; Xu, Y. et al. Rapid Through-Container Detection of Fake Spirits and Methanol Quantification with Handheld Raman Spectroscopy. Analyst 2019, 144, 324–330. DOI: 10.1039/c8an01702f
4. Gomes, A. A.; Azcarate, S. M.; Špánik, I. et al. Pattern Recognition Techniques in Food Quality and Authenticity: a Guide on How to Process Multivariate Data in Food Analysis. TrAC Trends Anal. Chem. 2023,164, 117105–117105. DOI: 10.1016/j.trac.2023.117105