SNIF-NMR

Over the years, Site-Specific Natural Isotope Fractionation (SNIF) NMR has been used extensively in food analysis. Deuterium ( H) is widely dispersed in the whole solar system and so it is as well on earth. Actually, the deuterium isotope ratio in water, usually expressed in parts per milhon (ppm - just 

A group or researcher at the Universite de Nantes, led by G. J. Martin authored a technical brochure on behalf of Bruker, a NMR instrument manufacturer, that provides good background material on SNIF-NMR [44]. Although the brochure focuses on the automation of wine NMR (the term used by the 

Studies on the distribution of short-chain acyl groups between primary secondary positions of triglycerides in fats, using high-resolution GLC and iR-NMR. 500-MHz iR NMR [63] 

The use of NMR to study the moisture content of various food products, including casein [64] butter bean. 0 NMR transverse relaxation rates. [64] 

Development of a computerized method to visualize bruises in apples. Magnetic Resonance Images [66] 

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Remaud GS, Martin YK, Giles G, Martin GJ (1997) Detection of natural vanilla flavors and extracts Application of the SNIF-NMR to vanillin and p-hydroxybenzaldehyde. J Agric Food Chem 45 859-866... 

Site-specific natural isotope fractionation (SNIP) NMR (SNIF-NMR) quantitative H-NMR measurements... 

SNIF-NMR and IRMS have been adopted as official methods by... 

More recently, enantiomer ratios have been used as evidence of adulteration in natural foods and essential oils. If the enantiomer distribution of achiral component of a natural food does not agree with that of a questionable sample, then adulteration can be suspected. Chiral GC analysis alone may not provide adequate evidence of adulteration, so it is often used in conjunction with other instrumental methods to completely authenticate the source of a natural food. These methods include isotope ratio mass spectrometry (IRMS), which determines an overall 13C/12C ratio (Mosandl, 1995), and site-specific natural isotope fractionation measured by nuclear magnetic resonance spectroscopy (SNIF-NMR), which determines a 2H/ H ratio at different sites in a molecule (Martin et al 1993), which have largely replaced more traditional analytical methods using GC, GC-MS, and HPLC. 

SD standard deviation SDE simultaneous distillation extraction SDS sodium dodecyl sulfate SFC solid fat content SFI solid fat index SHAM salicylhydroxamic acid SIM selected ion monitoring SNIF-NMR site-specific natural isotope fractionation measured by nuclear magnetic resonance spectroscopy SP-HPLC straight-phase high-performance liquid chromatography... 

A particular mention is needed for describing one analytical technique capable of detecting the exact site-specific isotope ratio. This technique, called SNIF-NMR (site specific natural isotope fractionating technique), constitutes the most specific and sophisticated method used for food authenticity determination. 

SNIF-NMR and/or IRMS techniques were often combined with trace element analyses (ICP-MS, ICP-OES, FAAS, ETAAS, GFFA) and chemometrics for the geographical characterization of wines. In a relatively old paper, Day et ah (1995) analyzed 165 grape samples collected in 1990 in four different production areas of France (Alsace, Beaujolais, Burgundy, and the Loire Valley). The combined use of isotopic and trace element data allowed an excellent classification of wine samples corresponding to... 

Ogrinc, N., Kosir, I. J., Kocjancic, M., and Kidric, J. (2001). Determination of authenticity, regional origin, and vintage of Slovenian wines using a combination of IRMS and SNIF-NMR analyses. J. Agric. Food Chem. 49,1432-1440. 

Remaud, G. S., Martin, Y. L., Martin, G. G., Naulet, N., and Martin, G. J. (1997). Authentication of mustard oils by combined stable isotope analysis (SNIF-NMR and IRMS). ]. Agric. Food Chern. 45,1844—1848. 

The first paper dealing with the NMR determination of non-random distribution of deuterium appeared in 1981 and the site-specific natural isotope fractionation studied by nuclear magnetic resonance (SNIF-NMR) terminology was proposed.36 Since this time several review articles on application of deuterium and 13C NMR natural abundance spectroscopy were published.37 1... 

Due to the inability to reliably detect beet sugar additions, the site-specific natural isotope fractionation nuclear magnetic resonance (SNIF-NMR) method used widely in the wine industry was adapted for the maple industry (Martin et al., 1996). This method determines the site specific isotope concentrations of organic compounds by nuclear magnetic resonance of ethanol fermented from the suspect sample. 

The biosynthetic origins of vanillin can be determined by the analysis of naturally occurring isotope ratios (in practice, chiefly 2H/1H and 13C/12C), using isotope ratio-mass spectrometry (IR-MS) and nuclear magnetic resonance (site-specific natural isotope fractionation SNIF-NMR ). Isotopic ratio... 

Remaud, C.S., Martin, Y.-L., Martin, C.C. and Martin, C.J. (1997) Detection of sophisticated adulterations of natural vanilla flavors and extracts application of the SNIF-NMR method to vanillin and p-hydroxyben-zaldehyde. Journal of Agricultural and Food Chemistry 45, 859-866. 

Site-specific measurement of isotope ratios can be made using site-specific natural isotope fractionation-nuclear magnetic resonance (SNIF-NMR). This was first proposed in 1981 by Martin and Martin [30], who then applied it to the adulteration of food (wine) in 1988 [31]. This technique allows D H ratios for specific H atoms within a molecule to be measured and can provide additional... 

In the final (and earliest) example to be presented in this section, Day et al. [29] utilized SNIF-NMR (individual D H ratios on the methyl and ethyl sites of the ethanol molecule), IRMS (O and D H ratio in the wine water C ratio in the wine distillate) ET-AAS (10 elements) and ICP-AES (Ba only). The concluding section of their paper sums up most of what has been written in this chapter and is strongly recommended for further reading, particularly as it represents possibly one of the earliest publications to describe the use of a multitechnique approach. 

An NMR spectrometer for SNIF-NMR (Fig. 6.17) (site-specific natural isotope fractionation NMR) measurements [226] must be specifically equipped and adapted, e.g. for deuterium analysis by a high field magnet (e.g. 9.4 T, corresponding to 400 MHz ( H) and 61.4 MHz ( H) resonance frequency, or 11.4 T, corresponding to 500 MHz ( H) and 76.8 MHz ( H) resonance frequency), a specifically adapted H-NMR probe with fluorine lock and proton decoupling, highly stable electronics and software for spectra acquisition and data processing/treatment. Instrumental details... 

Determinations of isotope patterns by SNIF-NMR (see 6.2.2.3.2) are by far of more practical importance (for an early review see [317]). Although up to now this methodology is nearly exclusively limited to the elucidation of H-pattems, recent attempts for its extension to C-pattem determinations have been promising. Normally only pure substances are used for H-NMR measurements >150 mg sample and several hours scans are needed. In the present context NMR spectral data of aromatic compounds, terpenes and some aliphatic compounds have been compiled. 

Table 6.13 Site-specific stable hydrogen isotope analysis of linalylacetate by SNIF-NMR. Adapted from [230] with kind permission. Copyright [1992] American Chemical Society. The overall D/H- and ( C/ C)-isotope ratios are determined by combustion and IRMS. S C-values are expressed in [%c[ V5. V-PDB, the overall D/H- and the site-specific D/H-ratios in parts per million [ppm], position indication see Fig. 6.22 (D/H) is the methyl group of the acetyl residue in this case...

G.J. Martin Deuterium-NMR in the investigation of site-specific natural isotope fractionation (SNIF-NMR) - Automation of wine NMR. Laboratoire de RMN et Reactivite Chimique Universite de Nantes - CNRS UA 472... 

G. Martin (1992) SNIF-NMR - eine Methode zum Nachweis von Riibenzuckerzusatz in Frucht-saften. Fliissiges Obst 52, 477-485... 

C. Fauhl, R. Wittkowski (1996) On-line H-NMR to facilitate tube preparation in SNIF-NMR analysis. Z. Lebensm. Unters. Forsch. 203, 541-545... 

G. Remaud (1993) Technical improvements of SNIF-NMR application to mustard oil. In 2" European Symposium Food Authenticity - Isotope Analysis and Other Advanced Analytical Techniques, 20-22 October 1993, Eurofins, Nantes (France)... 

G. Remaud, A.A. Debon, Y.-L. Martin, G.G. Martin, G.J. Martin (1997) Authentication of bitter almond oil and cinnamon oil application of the SNIF-NMR method to benzaldehyde. J. Agric. Food Chem. 45, 4042-4048... 

Site-specific natural isotope fractionation (SNIF) NMR, which determines different (D/H), isotope ratios from the NMR spectra, has been used to characterize essential oils derived from a variety of botanicals (lavender, spike lavender, bose de rose oil, bergamont, germanium, clary sage, petit grain, coriander, Formosan, and camphor oil) and geographical regions versus synthetically produced oils. These SNIF-NMR results combined with DA allowed the natural and synthetic oils to be unambiguously indentified. ... 

Chemometrics has been used to classify Apulian and Slovenian wines from H NMR.PCA, FA, LDA, and KNN analysis of nuclear magnetic resonance SNIF-NMR coupled with isotope ratio mass spectrometry (IRMS) has also been reported... 

Many applications of SNIF-NMR to the determination of the origin and quality of non-alcoholic products have been demonstrated.17 These include studies of the origin (natural or synthetic) of aromas and flavours such as vanillin337 338 and anethole,339 of vinegars340 and of possible adulteration of fruit juices and jams. The technique is expected to assume increasing importance in response to the demands of consumers and regulatory authorities for guarantees of food quality. 

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