8, 15 Our recent Fourier transform ion cyclotron resonance (FT‐ICR) MS study 15 revealed the presence of thousands of compounds in a large set of curated whisky samples. Lately, several studies have been carried out using high‐end MS techniques to characterise whisky. 12, 14 These methods are labour intensive to establish, often compound specific, and require several instruments and skilled operators to prepare the samples and interpret the results.
Traditionally, chemical analysis of whisky has used standard mass spectrometry (MS) techniques, in particular gas chromatography (GC)‐ and liquid chromatography (LC)‐MS, to identify and quantify its compounds, referred to as congeners. 12 Its production follows strict guidelines outlined in the Scotch Whisky Regulations (2009), 13 and yet every distillery produces a unique spirit. 6, 7, 8, 9, 10, 11 Scotch Whisky is produced by the fermentation of a cereal source, distillation to below 94.8% ( v/v) ethanol, and maturation in oak casks in Scotland for a minimum of 3 years. Chemical analysis of Scotch Whisky is therefore essential to gain a better understanding of the production processes and maturation chemistry 1, 2 as well as for addressing food safety challenges, 3, 4, 5 and authenticity concerns. Scotch Whisky is a culturally significant and high‐value commodity. The wealth of information obtained by these experiments will assist in NMR structure elucidation of Scotch Whisky congeners and generally the composition of alcoholic beverages at the molecular level. A 1D chemical‐shift‐selective TOCSY experiments was also modified. The developed solvent suppression procedure was integrated into several homocorrelated and heterocorrelated 2D NMR experiments, including 2D correlation spectroscopy (COSY), 2D total correlation spectroscopy (TOCSY), 2D band‐selective TOCSY, 2D J‐resolved spectroscopy, 2D 1H, 13C heteronuclear single‐quantum correlation spectroscopy (HSQC), 2D 1H, 13C HSQC‐TOCSY, and 2D 1H, 13C heteronuclear multiple‐bond correlation spectroscopy (HMBC). On the basis of the well‐established 1D nuclear Overhauser spectroscopy (NOESY) solvent suppression technique, this method suppresses the solvent at the beginning of the pulse sequence, producing pure phase signals minimally affected by the relaxation.
It is executed in automation allowing high throughput investigations of alcoholic beverages. The method uses 3 channels to suppress signals of water and ethanol, including those of 13C satellites of ethanol. Figure 1 – 1D 1H NMR spectrum of Scotch Whisky with only ‐OH signal suppressedįigure 2 – 1D 1H Reverse INEPT NMR spectrum of Scotch Whisky showing antiphase multiplets of 13C isotopomers of ethanolįigure 3 ‐ 1D 13C NMR spectrum of Scotch Whisky showing singlets for ethanolįigure 4 – 1D 1H NMR spectrum of Scotch Whisky with water and ethanol signals suppressedįigure 5 ‐ 2D 1H, 1H COSY NMR spectrum of Scotch Whiskyįigure 6 ‐ 2D 1H, 1H COSY NMR spectrum of Scotch Whisky with t 1 noise digitally removed using MestreNova 11įigure 7 ‐ 2D 1H, 1H TOCSY NMR spectrum of Scotch Whiskyįigure 8 ‐ 2D 1H, 1H TOCSY NMR spectrum of Scotch Whisky with t 1 noise digitally removed using MestreNova 11įigure 9 ‐ 2D 1H, 1H J‐Resolved NMR spectrum of Scotch Whiskyįigure 10 ‐ 2D 1H, 13C HSQC NMR spectrum of Scotch Whiskyįigure 11 ‐ 2D 1H, 13C HSQC NMR spectrum of Scotch Whisky with t 1 noise digitally removed using MestreNova 11įigure 12 ‐ 2D 1H, 13C HSQC‐TOCSY NMR spectrum of Scotch Whiskyįigure 13 ‐ 2D 1H, 13C HSQC‐TOCSY NMR spectrum of Scotch Whisky with t 1 noise digitally removed using MestreNova 11įigure 14 ‐ 2D 1H, 13C HMBC NMR spectrum of Scotch Whiskyįigure 15 ‐ 2D 1H, 13C HMBC NMR spectrum of Scotch Whisky with t 1 noise digitally removed using MestreNova 11Ī simple and robust solvent suppression technique that enables acquisition of high‐quality 1D 1H nuclear magnetic resonance (NMR) spectra of alcoholic beverages on cryoprobe instruments was developed and applied to acquire NMR spectra of Scotch Whisky.