Isotopic fingerprint method

Recently, deuterium-induced isotope effects on Li chemical shifts in organolithium compounds have been observed [51] and based on this observation, the isotopic fingerprint method was developed as a tool for structural investigations in the field of organolithium compounds. With this method, typical Li multiplets, which are characteristic of the aggregation state. 

The isotopic fingerprint method has been applied to study the aggregation of alkyl and aryl lithium compounds [51,52,72,73], of lithium disopropylamide [72] and of mixed aggregates between methyllithium and Lil [51] as well as LiBr [53]. These studies revealed also the existence of isotope shifts transmitted over more than two bonds. In all cases high-frequency shifts for the Li resonance were observed. 

Fingerprinting methods such as the anthocyanin methods and the Kirksey method for polyphenols (Kirksey el al., 1995) offer good ways to check for the addition of other fruits in a product. As the adulterators have become more sophisticated in the approaches that they use to extend juices, there has been a need for more complex methods of analysis. This means that it is now not uncommon to have to use fingerprinting techniques and isotopic methods to detect the most sophisticated forms of adulteration. These sophisticated analytical methods can even involve detection of the isotope ratios within a class of compounds such as sugars (Hammond el al., 1998). Using the RSSL 13C-IRIS approach, which was developed with financial support from the UK Food Standards Agency, it was possible to reduce the detection limit for the addition of C4-derived sugars to juices by about a factor of two. 

Biologically-derived compounds may be distinguished from similar compounds produced from a petrochemical source or from fossil fuel carbon by dual carbon-isotopic fingerprinting. This method can distinguish chemically identical materials (96). In addition, such methods have gained some importance in discriminating between natural and industrial pollution (97). 

The methods used to detect adulteration of juices have been reviewed by a number of authors and two examples are given here (Fry el al., 1995 Hammond, 1996). With the changing methods of unscrupulous suppliers it is now common to use a battery of tests to ensure that a product is authentic. Although this is costly, it is the only way to ensure the authenticity of a product and protect company reputations. The array of tests will often include a number of the procedures described above, such as sugar and acid profiles, along with other methods such as stable isotopic and fingerprinting procedures. 

The use of ICP-MS for elemental characterization in beverages has been covered by a recent review that emphasized the applications in the area of fingerprinting and authenticity assessment [48], The combination of (multi)elemental/ isotopic analyses with powerful multivariate statistical methods can provide a solution for the authentication of food and beverages [49] and there is an increasing awareness of the potential of ICP-MS in this respect. Foods originating from... 

It will be shown that the question of whether a localized or a delocalized excited state occurs can be answered also for Pt(2-thpy)2 by using the technique of isotope labeling combined with high-resolution spectroscopic methods and emission decay measurements. For this study, one compares suitable photophysical properties of perprotonated and perdeuterated compounds to those of partially deuterated ones. This procedure provides reliable fingerprints concerning the locahzation/delocahzation behavior [18,21 -23,33,47,48]. 

The use of these ions enables one to answer the preceding questions and we will examine below the new methodology required however, first we will propose several direct applications of this method (even in the case of mixtures) the origin of fragment ions, thus enabling veritable family trees of these ions to be produced the structure of molecules and the generation of fingerprints for their respective identification isotopic assay when the molecular peak is too small, or polluted by the presence of [M-H]" ions the localization of isotopes ( H, N, 0, etc.) the study of... 

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