Advanced solvent signal suppression for the acquisition of 1D and 2D NMR spectra of Scotch Whisky

Abstract

A simple and robust solvent suppression technique that enables acquisition of high-quality 1D ¹ H 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 ¹³ C 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 ¹ H, ¹³ C heteronuclear single-quantum correlation spectroscopy (HSQC), 2D ¹ H, ¹³ C HSQC-TOCSY, and 2D ¹ H, ¹³ C 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.

Keywords: 13C; 1H; NMR; Scotch Whisky; alcoholic beverages; complex mixture; solvent suppression.