Characterization of European wine glycerol: stable carbon isotope approach

Gas Chromatography Combustion Isotope Ratio Mass Spectrometry for Improving the Detection of Authenticity of Grape Must

Since ancient times, grape must and wine have been considered one of the most sophisticated matrices and, in the last few years, the continuous rise in volumes and prices of grapes and wine has encouraged fraud and adulteration in the oenological field. One of the most common adulterations is sugar addition to grape must in the form of cane or beet sugar or syrup coming from vegetable sources, such as cereals or fruits. Since 1990, the International Organisation of Vine and Wine (OIV) has issued specific official isotopic methods to fight against this practice, but they are not always effective. With the aim to develop a new method able to identify sugar addition, we compared the δ¹³C value of sugar extracted from grape must analyzed by elemental analyzer/isotope ratio mass spectrometry (EA-IRMS) to the δ¹³C value of proline analyzed by gas chromatography-combustion isotope ratio mass spectrometry (GC-C-IRMS), after extraction and derivatization. δ¹³C and δ¹⁵N of proline have also been tested as potential geographical markers. In addition, the carbon isotopic composition of two characteristic grape must sugars (myo- and scyllo-inositols) was measured by GC-C-IRMS, after derivatization, to identify the illegal correction of their concentration. On the basis of the obtained results we can conclude that the compound-specific isotope analysis represents a novel analytical tool to support and improve certification and control procedures.

Using stable isotope signatures to delineate the geographic point-of-origin of Keemun black tea

BACKGROUND

Confirmation of food labeling that claims production in a small geographic region is critical to traceability, quality control and brand protection. In the current study, isotope ratio mass spectrometry (IRMS) was used to generate profiles of δ¹³ C and δ¹⁵ N to determine if the stable isotope signatures of Keemun black tea differ within the three counties that claim production. Other factors (cultivar type, leaf maturity and manufacturing process) were considered for their potential effects.

RESULTS

Both cultivar type and leaf maturity have remarkable impact on the δ¹⁵ N values of tea leaves, and that the cultivar influenced the δ¹³ C values. Keemun black tea from Qimen county could be easily discriminated from samples from Dongzhi and Guichi counties based on δ¹⁵ N signatures. The k-NN model was cross-validated with an accuracy of 91.6%. Environmental factors and/or genotype seem to be the major reasons for δ¹⁵ N differences in Keemun black tea from the selected regions.

CONCLUSION

This article provides a potential effective method to delineate the geographic point-of-origin of Keemun black tea based on δ¹⁵ N signatures. © 2018 Society of Chemical Industry.

O-H-C isotope ratio determination in wine in order to be used as a fingerprint of its regional origin

Stable isotopes have been applied to determine the origin assignment and verify the geographical provenance that is considered important characteristics of wine products both for consumers and the international regulations, of wines. Stable isotope analyses of (18)O/(16)O, D/H and (13)C/(12)C ratio for the detection of origin and of adulteration in wine are discussed in this study. The δ(13)C analysis of ethanol and wines water δ(18)O underlines the importance of the photosynthetic pathway and the environmental conditions of wine. Also we discuss the main factors that are responsible for the differentiation of the oxygen isotope ratios of wine water. Data interpretation demonstrated the efficacy of δ(18)O analysis not only in the wine but also in grape berries, preferably if the determination of the δ(18)O value is employed together with the determination of the δ(2)H isotope content of wine, for the detection of the geographical origin of wine.

Intrinsic ratios of glucose, fructose, glycerol and ethanol 13C/12C isotopic ratio determined by HPLC-co-IRMS: toward determining constants for wine authentication

High-performance liquid chromatography linked to isotope ratio mass spectrometry (HPLC-co-IRMS) via a Liquiface© interface has been used to simultaneously determine (13)C isotope ratios of glucose (G), fructose (F), glycerol (Gly) and ethanol (Eth) in sweet and semi-sweet wines. The data has been used the study of wine authenticity. For this purpose, 20 authentic wines from various French production areas and various vintages have been analyzed after dilution in pure water from 20 to 200 times according to sugar content. If the (13)C isotope ratios vary according to the production area and the vintage, it appears that internal ratios of (13)C isotope ratios (R((13)C)) of the four compounds studied can be considered as a constant. Thus, ratios of isotope ratios are found to be 1.00 ± 0.04 and 1.02 ± 0.08 for R((13)C(G/F)) and R((13)C(Gly/Eth)), respectively. Moreover, R((13)C(Eth/Sugar)) is found to be 1.15 ± 0.10 and 1.16 ± 0.08 for R((13)C(Gly/Sugar)). Additions of glucose, fructose and glycerol to a reference wine show a variation of the R((13)C) value for a single product addition as low as 2.5 g/L(-1). Eighteen commercial wines and 17 concentrated musts have been analyzed. Three wine samples are suspicious as the R((13)C) values are out of range indicating a sweetening treatment. Moreover, concentrated must analysis shows that (13)C isotope ratio can be also used directly to determine the authenticity of the matrix.

Detection of counterfeit antiviral drug Heptodin and classification of counterfeits using isotope amount ratio measurements by multicollector inductively coupled plasma mass spectrometry (MC-ICPMS) and isotope ratio mass spectrometry (IRMS)

Isotope ratio mass spectrometry (IRMS) and multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS) are highly important techniques that can provide forensic evidence that otherwise would not be available. MC-ICP-MS has proved to be a very powerful tool for measuring high precision and accuracy isotope amount ratios. In this work, the potential of combining isotope amount ratio measurements performed by MC-ICP-MS and IRMS for the detection of counterfeit pharmaceutical tablets has been investigated. An extensive study for the antiviral drug Heptodin has been performed for several isotopic ratios combining MC-ICP-MS and an elemental analyser EA-IRMS for stable isotope amount ratio measurements. The study has been carried out for 139 batches of the antiviral drug and analyses have been performed for C, S, N and Mg isotope ratios. Authenticity ranges have been obtained for each isotopic system and combined to generate a unique multi-isotopic pattern only present in the genuine tablets. Counterfeit tablets have then been identified as those tablets with an isotopic fingerprint outside the genuine isotopic range. The combination of those two techniques has therefore great potential for pharmaceutical counterfeit detection. A much greater power of discrimination is obtained when at least three isotopic systems are combined. The data from these studies could be presented as evidence in court and therefore methods need to be validated to support their credibility. It is also crucial to be able to produce uncertainty values associated to the isotope amount ratio measurements so that significant differences can be identified and the genuineness of a sample can be assessed.

Inter-laboratory comparison of elemental analysis and gas chromatography/combustion/isotope ratio mass spectrometry. II. Delta15N measurements of selected compounds for the development of an isotopic Grob test

An inter-laboratory exercise was carried out by a consortium of five European laboratories to establish a set of compounds, suitable for calibrating gas chromatography/combustion/isotope ratio mass spectrometry (GC-C-IRMS) devices, to be used as isotopic reference materials for hydrogen, carbon, nitrogen and oxygen stable isotope measurements. The set of compounds was chosen with the aim of developing a mixture of reference materials to be used in analytical protocols to check for food and beverage authentication. The exercise was organized in several steps to achieve the certification level: the first step consisted of the a priori selection of chemical compounds on the basis of the scientific literature and successive GC tests to set the analytical conditions for each single compound and the mixture. After elimination of the compounds that turned out to be unsuitable in a multi-compound mixture, some additional oxygen- and nitrogen-containing substances were added to complete the range of calibration isotopes. The results of delta(13)C determinations for the entire set of reference compounds have previously been published, while the deltaD and delta(18)O determinations were unsuccessful and after statistical analysis of the data the results did not reach the level required for certification. In the present paper we present the results of an inter-laboratory exercise to identify and test the set of nitrogen-containing compounds present in the mixture developed for use as reference materials for the validation of GC-C-IRMS analyses in individual laboratories.

An improved method for the measurement of the isotope ratio of ethanol in various samples, including alcoholic and non-alcoholic beverages

The isotope ratios of ethanol, an important constituent or ingredient of some foods and various beverages and fuels, provide information about biological and geographical origin and quality. We have developed an improved method for measuring the isotope ratio of ethanol in various samples by gas chromatography-high temperature conversion or combustion-isotope ratio mass spectrometry (GC-TC/C-IRMS) with headspace solid-phase microextraction (HS-SPME). A HS-SPME method was developed by optimizing several different parameters, including salt addition, incubation temperature and time, and extraction time. The HS-SPME method enabled us to determine the isotope ratio at low ethanol concentrations (0.08 mM) in 50 min with good precision (+/-0.3 per thousand for delta(13)C and +/-5 per thousand for deltaD). An advantage of this technique is that it can be adapted for use with samples which have high viscosity and contain many matrix compounds, such as alcoholic and non-alcoholic beverages.

Inter-laboratory comparison of elemental analysis and gas chromatography combustion isotope ratio mass spectrometry (GC-C-IRMS). Part I: delta13C measurements of selected compounds for the development of an isotopic Grob-test

This study was directed towards investigating suitable compounds to be used as stable isotope reference materials for gas chromatography combustion isotope ratio mass spectrometry (GC-C-IRMS) calibration. Several compounds were selected from those used in the 'Grob-test' mixture. Oxygen- and nitrogen-containing substances were added to these compounds to allow the mixture to be used as a possible multi-isotopic calibration tool for 2H/1H, 13C/12C, 15N/14N and 18O/16O ratio determinations. In this paper we present the results of delta13C measurements performed by the consortium of the five laboratories taking part in this inter-calibration exercise. All the compounds were individually assessed for homogeneity, short-term stability and long-term stability by means of EA-IRMS, as required by the bureau communitaire de reference (BCR) Guide for Production of Certified Reference Materials. The results were compared then with the GC-C-IRMS measurements using both polar and non-polar columns, and the final mixture of selected compounds underwent a further certification exercise assessing limits of accuracy and reproducibility under specified GC-C-IRMS conditions.

Effects of must concentration techniques on wine isotopic parameters

Despite the robustness of isotopic methods applied in the field of wine control, isotopic values can be slightly influenced by enological practices. For this reason, must concentration technique effects on wine isotopic parameters were studied. The two studied concentration techniques were reverse osmosis (RO) and high-vacuum evaporation (HVE). Samples (must and extracted water) have been collected in various French vineyards. Musts were microfermented at the laboratory, and isotope parameters were determined on the obtained wine. Deuterium and carbon-13 isotope ratios were studied on distilled ethanol by nuclear magnetic resonance (NMR) and isotope ratio mass spectrometry (IRMS), respectively. The oxygen-18 ratio was determined on extracted and wine water using IRMS apparatus. The study showed that the RO technique has a very low effect on isotopic parameters, indicating that this concentration technique does not create any isotopic fractionation, neither at sugar level nor at water level. The effect is notable for must submitted to HVE concentration: water evaporation leads to a modification of the oxygen-18 ratio of the must and, as a consequence, ethanol deuterium concentration is also modified.

Forensic applications of isotope ratio mass spectrometry—A review

The key role of a forensic scientist is to assist in determining whether a crime has been committed, and if so, assist in the identification of the offender. Many people hold the belief that a particular item can be conclusively linked to a specific person, place or object. Unfortunately, this is often not achievable in forensic science. In performing their role, scientists develop and test hypotheses. The significance of those hypotheses that cannot be rejected upon completion of all available examinations/analyses is then evaluated. Although one can generally identify the substances present using available techniques, it is generally not possible to distinguish one source of the same substance from another. In such circumstances, although a particular hypothesis cannot be rejected, it cannot be conclusively proven, i.e. the samples could still have originated from different sources. This limitation of not being able to distinguish between sources currently extends to the analysis of other forensic samples including, but not limited to, ignitable liquids, paints, adhesives, textile fibres, plastics, and illicit drugs. Stable isotope ratio mass spectrometry (IRMS) is an additional technique that can be utilised to test a given hypothesis. This technique shows the potential to be able to individualise a range of materials of forensic interest. This paper provides a brief description of the technique, followed by a review of the various applications of IRMS in different scientific fields. The focus of this summary is on forensic applications of IRMS, in particular the analysis of explosives, ignitable liquids and illicit drugs.