Article

Caffeine in your drink: natural or synthetic?

Instrumental Analytical Chemistry, University of Duisburg-Essen, Essen, Germany.
Analytical Chemistry (impact factor: 5.86). 02/2012; 84(6):2805-10. DOI:10.1021/ac203197d pp.2805-10
Source: PubMed

ABSTRACT Owing to possible adulteration and health concerns, it is important to discriminate between natural and synthetic food ingredients. A new method for compound-specific isotope analysis (CSIA) by coupling high-temperature reversed-phase liquid chromatography to isotope ratio mass spectrometry (HT-RPLC/IRMS) was developed for discrimination of natural and synthetic caffeine contained in all types of drinks. The analytical parameters such as stationary phase, column inner diameter, and column temperature were optimized for the separation of caffeine directly from drinks (without extraction). On the basis of the carbon isotope analysis of 42 natural caffeine samples including coffee beans, tea leaves, guaraná powder, and maté leaves, and 20 synthetic caffeine samples from different sources by high-temperature reversed-phase liquid chromatography coupled to isotope ratio mass spectrometry, it is concluded that there are two distinguishable groups of caffeine δ(13)C-values: one between -25 and -32‰ for natural caffeine, and the other between -33 and -38‰ for synthetic caffeine. Isotope analysis by HT-RPLC/IRMS has been applied to identify the caffeine source in 38 drinks. Four mislabeled products were detected due to added but nonlabeled synthetic caffeine with δ(13)C-values lower than -33‰. This work is the first application of HT-RPLC/IRMS to real-world food samples, which showed several advantages: simple sample preparation (only dilution), high throughput, long-term column stability, and high precision of δ(13)C-value. Thus, HT-RPLC/IRMS can be a very promising tool in stable isotope analysis of nonvolatile compounds.

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    Article: Carbon isotope ratio measurements of glyphosate and AMPA by liquid chromatography coupled to isotope ratio mass spectrometry.
    Dorothea M Kujawinski, J Benjamin Wolbert, Lijun Zhang, Maik A Jochmann, David Widory, Nicole Baran, Torsten C Schmidt
    [show abstract] [hide abstract]
    ABSTRACT: The interest in compound-specific isotope analysis for product authenticity control and source differentiation in environmental sciences has grown rapidly during the last decade. However, the isotopic analysis of very polar analytes is a challenging task due to the lack of suitable chromatographic separation techniques which can be used coupled to isotope ratio mass spectrometry. In this work, we present the first method to measure carbon isotope compositions of the widely applied herbicide glyphosate and its metabolite aminomethylphosphonic acid (AMPA) by liquid chromatography coupled to isotope ratio mass spectrometry. We demonstrate that this analysis can be carried out either in cation exchange or in reversed-phase separation modes. The reversed-phase separation yields a better performance in terms of resolution compared with the cation exchange method. The measurement of commercial glyphosate herbicide samples show its principal applicability and reveals a wide range of δ(13)C values between -24 and -34 ‰ for different manufacturers. The absolute minimum amounts required to perform a precise and accurate determination of carbon isotope compositions of glyphosate and AMPA were in the sub-microgram range. The method proposed is sensitive enough to further perform the experiments that are necessary to better understand the carbon isotope fractionation associated to the natural degradation of glyphosate into AMPA. Furthermore, it can be used for contaminant source allocation and product authenticity as well.
    Analytical and Bioanalytical Chemistry 01/2013; · 3.78 Impact Factor
Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed. The impact factor represents a rough estimation of the journal's impact factor and does not reflect the actual current impact factor. Publisher conditions are provided by RoMEO. Differing provisions from the publisher's actual policy or licence agreement may be applicable.

Keywords

20 synthetic caffeine samples
 
42 natural caffeine samples
 
caffeine δ(13)C-values
 
carbon isotope analysis
 
coffee beans
 
compound-specific isotope analysis
 
coupling high-temperature reversed-phase liquid chromatography
 
guaraná powder
 
high-temperature reversed-phase liquid chromatography
 
Isotope analysis
 
isotope ratio mass spectrometry
 
natural caffeine
 
new method
 
nonlabeled synthetic caffeine
 
nonvolatile compounds
 
possible adulteration
 
real-world food samples
 
stable isotope analysis
 
synthetic caffeine
 
synthetic food ingredients
 

Lijun Zhang