Dunn Philip J H, Malinovsky Dmitry, Goenaga-Infante Heidi
LGC Limited, Queens Road, Teddington, Middlesex, TW11 0LY, UK,
Anal Bioanal Chem. 2015 Apr;407(11):3169-80. doi: 10.1007/s00216-014-7926-1. Epub 2014 Jun 8.
We report a methodology for the determination of the stable carbon absolute isotope ratio of a glycine candidate reference material with natural carbon isotopic composition using EA-IRMS. For the first time, stable carbon absolute isotope ratios have been reported using continuous flow rather than dual inlet isotope ratio mass spectrometry. Also for the first time, a calibration strategy based on the use of synthetic mixtures gravimetrically prepared from well characterised, highly (13)C-enriched and (13)C-depleted glycines was developed for EA-IRMS calibration and generation of absolute carbon isotope ratio values traceable to the SI through calibration standards of known purity. A second calibration strategy based on converting the more typically determined delta values on the Vienna PeeDee Belemnite (VPDB) scale using literature values for the absolute carbon isotope ratio of VPDB itself was used for comparison. Both calibration approaches provided results consistent with those previously reported for the same natural glycine using MC-ICP-MS; absolute carbon ratios of 10,649 × 10(-6) with an expanded uncertainty (k = 2) of 24 × 10(-6) and 10,646 × 10(-6) with an expanded uncertainty (k = 2) of 88 × 10(-6) were obtained, respectively. The absolute carbon isotope ratio of the VPDB standard was found to be 11,115 × 10(-6) with an expanded uncertainty (k = 2) of 27 × 10(-6), which is in excellent agreement with previously published values.
我们报告了一种使用元素分析仪-同位素比质谱仪（EA-IRMS）测定具有天然碳同位素组成的甘氨酸候选参考物质的稳定碳绝对同位素比的方法。首次使用连续流而非双进样同位素比质谱法报告了稳定碳绝对同位素比。同样也是首次开发了一种校准策略，该校准策略基于使用由特征明确、高度富集(^{13}C)和贫化(^{13}C)的甘氨酸重量法制备的合成混合物，用于EA-IRMS校准并通过已知纯度的校准标准生成可溯源至国际单位制（SI）的绝对碳同位素比值。还使用了基于利用文献中关于维也纳皮迪迪贝莱姆石（VPDB）本身的绝对碳同位素比的值将更常测定的维也纳皮迪迪贝莱姆石（VPDB）标度上的δ值进行转换的第二种校准策略进行比较。两种校准方法得到的结果均与先前使用多接收电感耦合等离子体质谱仪（MC-ICP-MS）对同一种天然甘氨酸所报告的结果一致；分别获得了绝对碳比为(10,649×10^{-6})，扩展不确定度（(k = 2)）为(24×10^{-6})以及绝对碳比为(10,646×10^{-6})，扩展不确定度（(k = 2)）为(88×10^{-6})。发现VPDB标准的绝对碳同位素比为(11,115×10^{-6})，扩展不确定度（(k = 2)）为(27×10^{-6})，这与先前发表的值非常吻合。
