Natural stable isotope ratios for carbon, hydrogen and oxygen depend on the origin of the studied chemical compound. Such a precept is the basis of the control of the authenticity of food and especially alcoholic beverages. 13C/12C analysis of ethanol as well as 180/160 determination of water contained in wines from different European countries underline the importance of the photosynthetic pathway as well as of the environmental and climatological conditions of the vine. Interesting results in agreement with isotopic fractionation rules for the geographical origin of the samples were obtained. That encouraged us to propose the establishment of a database for isotopic parameters in wines. Stable aboutisotope ratio analysis can yield information the origin of a chemical compound. Natural stable isotope"abundances for elements such as H , C and 0 show small but measurable variations ( Fig. 1) due to isotopic fractionation which occurs during the chemical and physical processes of the natural cycles. '-4 The primary carbon pools in nature are HCO; in the hydrosphere and C 0 2 in the atmosphere. The use of isotope ratio mass spectrometry (IRMS) applied to the carbon bioelement has underlined the I3C discrimination of plants.In C3 plants, including the vine (Calvin photosynthetic cycle), the interstomatal diffusion of C 0 2 and also its dissolution cause negligible isotopic fractionation compared to the carboxylation of ribulose 1,5-biphosphate. Therefore C3 plants show a 6I3C range between -32%, and -25%0 PDB (Pee-Dee Belemnite, SC, USA).5*6 In the C4 plants (Hatch and Slack photosynthetic cycle) both the interstomatal diffusion of C 0 2 and the carboxylation of phosphoenolpyruvate limit the C 0 2 fixation and control the carbon isotopic content of those plant^.^,^ The so-called 'Crassulacean Acid Metabolism' (CAM) plants demonstrate an adaptation capacity in keeping with their environmental Such a difference in the stable carbon isotope content has often been used to detect adulteration of aromas and flavors, especially with gas chromat~graphy/'~C-I~C IRMS instruments,' (e.g. , sweetening of maple syrup) and also to establish the authenticity of wine products and spirit^.^. 3. I", Atmospheric O2 and C02, as well as H 2 0 , are the major sources of the oxygen element. Isotopic fractionation occurs during the various evapo-condensation processes. Clouds are lower in "0 than ocean water; meteoric waters are enriched in compared to clouds. The fermentation process causes no enrichment in the "0 content of the water. Due to the I*O enrichment of plant water compared to exogenous water (tap water), "0 measurements have also been used to ' detect the watering of wines as well as the redilution of fruit Water is the major pool of the hydrogen bioelement, too. As is observed for oxygen, an isotopic fractionation of hydrogen takes place during the evapocondensation process in the atmosphere, and during evaporation and biochemical reactions in plants. During the fermentation process an enrichment in 2H of wine water is obser...
A collaborative study of the site-specific natural isotope fractionation-nuclear magnetic resonance (SNIF-NMR) method for detecting added beet sugar in fruit juices is reported. This method is complementary to the stable carbon isotope ratio analysis (SCIRA) (AOAC Official Methods 981.09 and 982.21), which can detect sugars derived from plants exhibiting C4 metabolism (corn and sugarcane). It is based on the fact that the deuterium content at specific positions of the sugar molecules is higher in fruit sugars than in beet sugar. The fruit juices are fermented, and the alcohol is distilled with a quantitative yield and analyzed with a highfield NMR spectrometer fitted with a deuterium probe and fluorine lock. The proportion of ethanol molecules monodeuterated on the methyl site is recorded. This parameter (D/H)i is lowered when beet sugar is added to a fruit juice or concentrate. The precision of that method for measuring (D/H)i was observed to be similar to that of other isotope ratio methods: sr values ranged from 0.19 to 0.25 ppm and SR values varied between 0.21 and 0.37 ppm. An excellent correlation was observed between the percentage of added beet sugar and the (D/H)i isotope ratio measured in this collaborative study. Consequently, all samples in which beet sugar was added were found to have a (D/H)i isotope ratio significantly below the normal value for authentic juice or concentrate of that fruit. The SNIF-NMR method for detection of added beet sugar in fruit juices has been adopted by AOAC INTERNATIONAL.
From 1991 to 1997, nine intercomparison exercises on rainwater and freshwater samples were held in the framework of an activity connecting laboratories participating in different projects (Environmental studies in the Mediterranean basin, Italian network for the study of wet deposition, Acidification of mountain lakes, Limnological studies of Lake Léman, Monitoring of atmospheric deposition in forests). The number of participants increased from 72 in 1991 to 177 in 1997. Among the measured variables (pH, conductivity, alkalinity, major ions and nutrients), Ca, Mg, Na, K, ammonium, sulphate, chloride and nitrate are considered in this paper. The methods commonly used by the laboratories involved in the exercises are compared for precision, and an estimate of the performance of each method at different concentrations is made. The results show that some of the participating laboratories use analytical methods which are not reliable for the concentration values occurring in freshwater and/or in rainwater. However, outliers are also produced by laboratories using well-performing methods, indicating the importance of introducing analytical control procedures
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