Abstract
A 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. The method uses 3 channels to suppress signals of water and ethanol, including those of 13C satellites of ethanol. It is executed in automation allowing high throughput investigations of alcoholic beverages. 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. 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). A 1D chemical‐shift‐selective TOCSY experiments was also modified. 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.
Highlights
Scotch Whisky is a culturally significant and high value commodity
We present an automated ethanol/water solvent suppression methodology allowing for the acquisition of high resolution, high sensitivity 1D 1H NMR spectra of whisky with minimal sample preparation
Scotch Whisky is an acidic solution, with acidity increasing during maturation
Summary
Scotch Whisky is a culturally significant and high value commodity. Chemical analysis of ScotchWhisky is 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.[6,7,8,9,10,11] Scotch Whisky is produced by the fermentation of a cereal source, distillation to below94.8% (v/v) ethanol, and maturation in oak casks in Scotland for a minimum of three years.[12]. Scotch Whisky is a culturally significant and high value commodity. Whisky is 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.[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 three years.[12] Its production follows strict guidelines outlined in the Scotch Whisky Regulations (2009)[13], and yet every distillery produces a unique spirit. Chemical analysis of whisky has used standard MS techniques, in particular GC- and LCMS, to identify and quantify its compounds, referred to as congeners.[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
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