Thomas Freddy, Jamin Eric
Eurofins Scientific Analytics, BP42301, 44323 Nantes, France.
Anal Chim Acta. 2009 Sep 1;649(1):98-105. doi: 10.1016/j.aca.2009.07.014. Epub 2009 Jul 10.
An international collaborative study of isotopic methods applied to control the authenticity of vinegar was organized in order to support the recognition of these procedures as official methods. The determination of the 2H/1H ratio of the methyl site of acetic acid by SNIF-NMR (site-specific natural isotopic fractionation-nuclear magnetic resonance) and the determination of the 13C/12C ratio, by IRMS (isotope ratio mass spectrometry) provide complementary information to characterize the botanical origin of acetic acid and to detect adulterations of vinegar using synthetic acetic acid. Both methods use the same initial steps to recover pure acetic acid from vinegar. In the case of wine vinegar, the determination of the 18O/16O ratio of water by IRMS allows to differentiate wine vinegar from vinegars made from dried grapes. The same set of vinegar samples was used to validate these three determinations. The precision parameters of the method for measuring delta13C (carbon isotopic deviation) were found to be similar to the values previously obtained for similar methods applied to wine ethanol or sugars extracted from fruit juices: the average repeatability (r) was 0.45 per thousand, and the average reproducibility (R) was 0.91 per thousand. As expected from previous in-house study of the uncertainties, the precision parameters of the method for measuring the 2H/1H ratio of the methyl site were found to be slightly higher than the values previously obtained for similar methods applied to wine ethanol or fermentation ethanol in fruit juices: the average repeatability was 1.34 ppm, and the average reproducibility was 1.62 ppm. This precision is still significantly smaller than the differences between various acetic acid sources (delta13C and delta18O) and allows a satisfactory discrimination of vinegar types. The precision parameters of the method for measuring delta18O were found to be similar to the values previously obtained for other methods applied to wine and fruit juices: the average repeatability was 0.15 per thousand, and the average reproducibility was 0.59 per thousand. The above values are proposed as repeatability and reproducibility limits in the current state of the art. On the basis of this satisfactory inter-laboratory precision and on the accuracy demonstrated by a spiking experiment, the authors recommend the adoption of the three isotopic determinations included in this study as official methods for controlling the authenticity of vinegar.
为了支持将这些方法认定为官方方法，组织了一项关于应用同位素方法控制醋真实性的国际合作研究。通过SNIF-NMR（位点特异性天然同位素分馏-核磁共振）测定乙酸甲基位点的2H/1H比值，以及通过IRMS（同位素比值质谱法）测定13C/12C比值，可为表征乙酸的植物来源和检测使用合成乙酸对醋进行的掺假提供补充信息。两种方法都采用相同的初始步骤从醋中回收纯乙酸。对于葡萄酒醋，通过IRMS测定水的18O/16O比值可以区分葡萄酒醋和由干葡萄制成的醋。使用同一组醋样品对这三种测定方法进行验证。发现测量δ13C（碳同位素偏差）方法的精密度参数与先前应用于葡萄酒乙醇或从果汁中提取的糖的类似方法所获得的值相似：平均重复性（r）为千分之0.45，平均再现性（R）为千分之0.91。正如先前内部对不确定度的研究所预期的那样，发现测量甲基位点2H/1H比值方法的精密度参数略高于先前应用于葡萄酒乙醇或果汁中发酵乙醇的类似方法所获得的值：平均重复性为1.34 ppm，平均再现性为1.62 ppm。该精密度仍明显小于各种乙酸来源之间的差异（δ13C和δ18O），并能对醋的类型进行令人满意的区分。发现测量δ18O方法的精密度参数与先前应用于葡萄酒和果汁的其他方法所获得的值相似：平均重复性为千分之0.15，平均再现性为千分之0.59。上述值被提议作为当前技术水平下的重复性和再现性限值。基于这种令人满意的实验室间精密度以及加标实验所证明的准确性，作者建议采用本研究中包含的三种同位素测定方法作为控制醋真实性的官方方法。
