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Application of automated eightfold suppression of water and ethanol signals in 1 H NMR to provide sensitivity for analyzing alcoholic beverages
Author(s) -
Monakhova Yulia B.,
Schäfer Hartmut,
Humpfer Eberhard,
Spraul Manfred,
Kuballa Thomas,
Lachenmeier Dirk W.
Publication year - 2011
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.2823
Subject(s) - chemistry , ethanol , acetaldehyde , alcohol , analytical chemistry (journal) , pulse sequence , methanol , dilution , sensitivity (control systems) , proton nmr , chromatography , signal (programming language) , nuclear magnetic resonance , stereochemistry , organic chemistry , thermodynamics , computer science , engineering , programming language , physics , electronic engineering
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.