Stockwell Marc, Goodall Ian, Uhrín Dušan
EaStCHEM School of Chemistry Joseph Black Building University of Edinburgh Edinburgh UK.
The Robertson Trust Building Research Avenue North, Riccarton The Scotch Whisky Research Institute Edinburgh UK.
Anal Sci Adv. 2020 Jul 27;1(2):132-140. doi: 10.1002/ansa.202000063. eCollection 2020 Aug.
Whisky is a complex mixture made up of thousands of compounds originating in different stages of its production. Analysis of whisky congeners is critical to our understanding of the manufacturing process, quality control, and the detection of counterfeit products. The current chromatographic methods have a long analysis time, can require milliliters of sample and may not detect all required compounds in a single analysis. We have demonstrated that the majority of the whisky congeners of interest can be analyzed using H NMR spectroscopy in a single session using 500 μL of sample with the addition of 100 μL of buffer. We addressed two issues with this application of NMR: sensitivity and complexity of spectra. The sensitivity issues were solved by using a highly sensitive 600 MHz instrument equipped with a cryoprobe. To achieve consistent quantitative analysis of overlapping signals, Chenomx software was used. This allowed successful determination of the absolute concentration of 13 of the 21 studied whisky congeners with an average relative difference from nominal concentration of 6.4% and a standard deviation of 5.0%. Some compounds such as iso-amyl acetate and -butanol were not accurately quantifiable due to their low concentration and overlapping peaks with those of more concentrated compounds. Scopoletin, lactose, sucrose, and maltose were not detectable in whisky samples, but they were accurately quantified in model mixtures. At higher concentrations, these compounds could be accurately quantified in whisky samples. Overlap of glucose and fructose signals led to >10% deviations from nominal concentration values. The limits of quantification (LOQ) and limits of detection (LOD) for each analyte were determined, with the LOD varying between 10 and 20 μM for the major volatile congeners, 1 to 5 μM for maturation related congeners, and 10 to 30 μM for carbohydrates.
威士忌是一种复杂的混合物，由数千种源自其生产不同阶段的化合物组成。对威士忌同系物的分析对于我们理解制造过程、质量控制和假冒产品检测至关重要。目前的色谱方法分析时间长，可能需要数毫升样品，并且在一次分析中可能无法检测到所有所需化合物。我们已经证明，使用核磁共振氢谱（H NMR）光谱，在加入100 μL缓冲液的情况下，仅用500 μL样品，就可以在一次实验中分析大多数感兴趣的威士忌同系物。我们针对核磁共振在该应用中的两个问题进行了研究：灵敏度和光谱复杂性。通过使用配备低温探头的高灵敏度600 MHz仪器解决了灵敏度问题。为了实现对重叠信号的一致定量分析，使用了Chenomx软件。这使得成功测定了21种研究的威士忌同系物中的13种的绝对浓度，与标称浓度的平均相对差异为6.4%，标准偏差为5.0%。一些化合物，如乙酸异戊酯和正丁醇，由于其浓度低且与更浓缩化合物的峰重叠，无法准确定量。在威士忌样品中未检测到东莨菪素、乳糖、蔗糖和麦芽糖，但在模型混合物中对它们进行了准确的定量。在较高浓度下，这些化合物可以在威士忌样品中准确定量。葡萄糖和果糖信号的重叠导致与标称浓度值的偏差超过10%。确定了每种分析物的定量限（LOQ）和检测限（LOD），主要挥发性同系物的LOD在10至20 μM之间，与陈酿相关的同系物的LOD在1至5 μM之间，碳水化合物的LOD在10至30 μM之间。
