instrumental techniques applied to mineralogy and geochemistry

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88 Clemente Recio Something similar happens for H and O, which require different reactors, and that cannot, therefore, be measured from the same aliquot. LC-IRMS The main problem associated to GC-C-IRMS is that samples need to be soluble in a suitable volatile solvent. If they are not, they need to be derivatized to a suitable form. But derivatization can affect the isotopic results. Fractionation can occur either by kinetic effects or incomplete conversion, and the derivatizing agent adds extraneous C, and maybe other elements as well. Coupling a liquid chromatograph to the IRMS may overcome some of these problems. However, LC-IRMS requires that the liquid phase be prevented from reaching the mass spectrometer, eliminating it either before or after oxidation of the sample of interest. Several solutions have been proposed to this end, such as nebulizing the LC effluent and reacting the sample in a plasma; placing the effluent in a moving wire or belt, evaporating the solvent and combusting the dry sample, or else oxidizing the sample to CO 2 while still dissolved, and separating the CO 2 afterwards. Whatever the approach, the technique is useful to analyze high molecular weight compounds not well suited for GC-IRMS, such as sugars, aminoacids or active components of pharmaceuticals and drugs. Applications and uses Food and food fraud Food and food-related products represent a large percentage of GDP. They also are a major component to be considered within the average family's domestic economy. Additionally, certain products are perceived as of higher quality on grounds such as provenance (“Denominación de Origen” –DO-; “Apellation d’Origine Contrôlée et Garantie” –AOCG-, …), growing and/or breeding method (“Organically Grown Product”) or health benefits, and as such reach substantially higher market prices, warranting the need for objective quality and provenance control methods. Since the physical, chemical or biochemical reasons underpinning isotope fractionation can be affected by factors such as geography (climate, altitude, latitude,…), species and variety, culture method, … etc., each product to be considered requires
Alike as two water drops: distinguishing one source of the same substance from another 89 establishing a suitable database to be used as reference. In Europe, this is done through the European Commission's Joint Research Centre (JRC), who establishes validated methods, analytical standards, and mutually recognized approaches to analytical quality assurance (Table 1). TABLE 1. Official EU analytical methods employing isotope data, and current projects (Calderone et al., 2003). Product Official method / Research Project Application Wine UE # 2676/90, 822/97, 440/2003, Chaptalization, Geographycal OIV ré. ENO 2/96, ENO 17/2001, provenance, Watering. Wine-DB, GLYCEROL Alcohol OIV, BEVABS Botanical origin, Ethanol Spirits OIV, BEVABS Botanical origin Sugar SUGAR 18 O Botanical origin Honey AOAC method 999.41 Addition of sugars Perfumeand Fragance GCC-IRMS Botanical origin, anethol, vainillin Dairy and cheese MILK Geographycal provenance Fruit juice CEN/TC #s. 108, 109, 110, AOAC method 995.17, SUGAR 18 O Addition of sugars, Dilution Oil and fat MEDEO Origin Fish COFAWS Geographycal provenance; Wild / Cultured Vinager OIV Botanical origin The term "food" normally includes a complex and highly variable set of products, both natural and at various stages of processing, making it extremely difficult to define detailed chemical compositions that are common to a range of products. Stable isotope distribution, however, responds to fundamental processes, that are fixed at primary production, thus providing a suitable method to test for the authenticity of the items of interest. As it is not commercially viable to circumvent isotopic detection, stable isotopes have provided a way to detect fraud in products as diverse as, among many others, honey, fruit juices, wine, milk and dairy, Iberian ham, vegetable oil, mineral waters, beverages, food additives and even animal feed (i.e., Rossmann, 2001). An actual example of how stable isotopes can be used is that of Fig. 1, where the 13 C and 15 N of the solid extract of locally purchased beer has been plotted according to the ingredients declared in the label. All beers brewed according to the “Bavarian Purity Law” of 1516 have 13 C < -25‰, as do the wheat and most pure barley malt
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