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On-line1H-NMR to facilitate tube preparation in SNIF-NMR analysis

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Abstract

The detection of adulteration of wine by SNIF-NMR (site-specific natural isotopic fractionation-nuclear magnetic resonance) analysis of wine alcohol is a well established and widely used method. Quantitative deuterium ([2H]) NMR spectroscopy of defined distillate/tetramethylurea (TMU) mixtures enables the calculation of the site-specific deuterium/hydrogen ([2H]/H) ratios in the ethanol molecule. TMU with a known [2H]/H ratio serves as the internal standard. The comparison of the [2H]/H ratios of unknown samples with values obtained from authentic samples allows conclusions to be drawn, in terms of the origin of the sugar in the must before fermentation. Up to now, the calculation of [2H]/H ratios has required the exact weighing of both the distillate and the quantity of TMU for the tube preparation, as they affect2H-NMR measurements. The precise quantity of ethanol in the distillates must be determined by Karl-Fischer titration or densitometry. Volatile distillate components are quantified by gas chromatography to ensure a satisfactory purity of the ethanol under study. The quantitative1H-NMR method described involves determining the TMU/ethanol mass ratios in the tubes prepared for SNIF-NMR measurements. This mass ratio is necessary for the calculation of the [2H]/H ratio. The mass ratios measured using conventional procedures and those determined by on-line1H-NMR agree 100%. Using this method means that the exact weighing of distillates and TMU for tube preparation and the determination of ethanol content in the distillates are no longer required. At the same time, higher concentrations of volatile components in the distillates, e.g. methanol, can be easily detected.

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Authors and Affiliations

  1. Bundesinstitut für gesundheitlichen Verbraucherschutz und Veterinärmedizin, Postfach 33 00 13, D-14191, Berlin, Germany

    C. Fauhl & R. Wittkowski

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  1. C. Fauhl
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  2. R. Wittkowski
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Fauhl, C., Wittkowski, R. On-line1H-NMR to facilitate tube preparation in SNIF-NMR analysis. Z Lebensm Unters Forch 203, 541–545 (1996). https://doi.org/10.1007/BF01193160

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  • DOI: https://doi.org/10.1007/BF01193160

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