Application of automated eightfold suppression of water and ethanol signals in 1 H NMR to provide sensitivity for analyzing alcoholic beverages

The 400 MHz 1 H NMR analysis of alcoholic beverages using standard pulse programs lacks the necessary sensitivity to detect minor constituents such as methanol, acetaldehyde or ethyl acetate. This study investigates the application of a shaped pulse sequence during the relaxation delay to suppress the eight 1 H NMR frequencies of water and ethanol (the OH singlet of both water and ethanol, as well as the CH 2 quartet and CH 3 triplet of ethanol). The sequence of reference measurement for frequency determination followed by the suppression experiment is controlled by a macro in the acquisition software so that a measurement under full automation is possible (12 min per sample total time). Additionally, sample preparation was optimized to avoid precipitation, which is facilitated by 1 : 1 dilution with ethanol and pH 7.4 buffer. Compared with the standard water presaturation pulse program, the eightfold suppression allowed a significantly higher setting of receiver gain without receiver overflow, which significantly increased the signal‐to‐noise ratio by an average factor of 10. The signal intensities increased by a factor of 20. The resulting limits of detection (below 1 g/hl of pure alcohol) now allow the control of legal requirements for minor compounds in alcoholic beverages. Copyright © 2011 John Wiley & Sons, Ltd.