Isotope ratio mass spectrometry food research

Faulharber et al (5,6) and other researchers (7-9) have described how the determination of the isotope values of constituents is of increasing importance, especially in view of the demand for authenticity control and origin determination of essential oils and foods. To determine isotope values, g chromatography-isotope ratio mass spectrometry (GC-IRMS) has been used, although not widely. The present authors (70) have studied the possibility of a more convenient and common means of analysis of isotope values, based on the isotope peak in the mass spectrum of a compound. The present study focuses on the development of a new analytical method for the differentiation of quality in commercial citrus oils of various origins. 

Contrary to the predictions in 1989 (27), LC-MS has not experienced a breakthrough as an analytical technique in the vitamin E area. One research group reported two studies on the determination of liposoluble vitamins in foods and infant formulas by LC-particle beam MS (44,50). Caimi and Brenna coupled HPLC with combustion isotope ratio mass spectrometry for the analysis of mixtures of liposoluble vitamins, including a- and y-tocopherol (171). 

In all these applications, isotope ratio data are produced, which are interpreted on an absolute or relative basis and which have an impact on our daily life, whether this is in science (e.g., age of an artifact), in society (e.g., provenance of food), or in public safety (e.g., neutron shielding in nuclear power plants). To ensure that these data are reliable and accurate, some specific requirements have to be fulfilled. The main requirement is that all these measurement results are comparable, which means that the corresponding results can be compared and differences between the measurement results can be used to draw further conclusions. This is only possible if the measurement results are traceable to the same reference [25]. This in turn can only be realized by applying isotopic reference materials (IRMs) for correction for bias and for validation of the analytical procedure. Whereas in earlier days only experts in mass spectrometry were able to deliver reproducible isotope ratio data, nowadays many laboratories, some of which may even have never been involved with mass spectrometry before, produce isotope ratio data using inductively coupled plasma mass spectrometry (ICP-MS). Especially for such users, IRMs are indispensable to permit proper method validation and reliable results. The rapid development and the broad availability of ICP-MS instrumentation have also led to an expansion of the research area and new elements are under investigation for their isotopic variations. In this context, all users require IRMs to correct for instrumental mass discrimination or at least to allow isotope ratio data to be related to a commonly accepted basis. 

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