Flow Injection Analysis−Isotope Ratio Mass Spectrometry for Bulk Carbon Stable Isotope Analysis of Alcoholic Beverages

Abstract

A new method for bulk carbon isotope ratio determination of water-soluble samples is presented that is based on flow injection analysis-isotope ratio mass spectrometry (FIA-IRMS) using an LC IsoLink interface. Advantages of the method are that (i) only very small amounts of sample are required (2-5 microL of the sample for up to 200 possible injections), (ii) it avoids complex sample preparation procedures such as needed for EA-IRMS analysis (only sample dilution and injection,) and (iii) high throughput due to short analysis times is possible (approximately 15 min for five replicates). The method was first tested and evaluated as a fast screening method with industrially produced ethanol samples, and additionally the applicability was tested by the measurement of 81 alcoholic beverages, for example, whiskey, brandy, vodka, tequila, and others. The minimal sample concentration required for precise and reproducible measurements was around 50 microL L(-1) ethanol/water (1.71 mM carbon). The limit of repeatability was determined to be r=0.49%. FIA-IRMS represents a fast screening method for beverage authenticity control. Due to this, samples can be prescreened as a decisive criterion for more detailed investigations by HPLC-IRMS or multielement GC-IRMS measurements for a verification of adulteration.

High‐temperature reversed‐phase liquid chromatography coupled to isotope ratio mass spectrometry

“…In addition to δ 13 C measurements, LC/IRMS could be used for compound quantification based on the fact that the carbon amount of analytes injected is proportional to the measured peak areas or amplitudes. In this work, the method detection limit (MDL) of HT‐RPLC/IRMS was tested on the XBridge C 18 column at 120 °C and the Acquity C 18 column at 150 °C by injection of caffeine at concentrations between 20 and 500 mg L –1 following a previously described moving mean approach . Within this concentration range the relationship between the peak area of 44 CO 2 and concentration showed good linearity (R ≥0.99).…”

“…However, the triplicate measurements of caffeine at 20 mg L –1 had a low precision with SD higher than 0.70‰. Therefore, 30 mg L –1 of caffeine (12.4 nmol carbon on‐column) was defined as the MDL, which is close to the MDL of ethanol (8.7 nmol carbon on‐column) measured by FIA‐IRMS . The same concentration range of caffeine from 30 to 500 mg L –1 (corresponding to 12.4 to 206.0 nmol carbon on‐column) was also obtained for quantification measurement and δ 13 C determination on the Acquity C 18 column at 150 °C, yielding the same MDL (results not shown).…”

Liquid chromatography/mass spectrometry stable isotope analysis of dissolved organic carbon in stream and soil waters

“…The device, which was specially developed for on‐line compound‐specific isotope analysis of water‐soluble samples after LC separation, can also be used without a column in bulk mode analysis for simple and macromolecular compounds . In the field of complex raw samples the LC IsoLink interface has been already used for bulk carbon isotope ratio determination in alcoholic beverages . The main advantage of this method is that the water sample is injected into a continuous flow of mobile phase (ultrapure deionised water) and reagents mixed at the entry of a heated capillary reactor connected on‐line to an open‐split coupling and to the IRMS system via a liquid/gas (water/He) membrane exchanger and a gas‐drying unit (see Krummen et al .…”

The Analysis of Vodka: A Review Paper

“…Eight out of 10 samples were classified as the vodkas produced from potatoes or from crops such as rye and wheat. The remaining two samples were classified as the ones produced from molasses, which is a by-product of sugar cane processing (Jochmann et al 2009). This method is effective in investigation of botanic origin of the samples, which can be especially useful in the case of vodka, the producers of which provide its composition on labels.…”