Stable isotope analysis of non-exchangeable hydrogen in carbohydrates derivatised with N-methyl-bis-trifluoroacetamide by gas chromatography – Chromium silver reduction/High temperature Conversion-isotope ratio mass spectrometry (GC-CrAg/HTC-IRMS)

Abstract

A novel procedure for the rapid isotope analysis of the carbon-bound non-exchangeable (CBNE) hydrogen in mono and disaccharides has been developed to demonstrate the feasibility of detecting undeclared addition of exogenous sugar products in foods and beverages susceptible to economically motivated adulteration. The procedure utilizes a simple one-step reaction, with the derivatising agent N-methyl-bis-trifluoroacetamide, to substitute the exchangeable hydroxyl-hydrogens with trifluoroacetate derivatives that are sufficiently volatile to be separated and measured by a gas chromatograph coupled to an isotope ratio mass spectrometer. The conversion of the derivatised sugars into the measuring gas is achieved using a high temperature chromium-silver reactor that retains carbon, oxygen and fluorine whilst releasing hydrogen gas for stable isotope measurement. The new procedure has advantages over existing methods in terms of ease of use, analysis time and compound-specific information. Sugars from fruit juice and honey have been measured to demonstrate the feasibility of using this technique.