Werner Roland A
Max-Planck-Institut für Biogeochemie, P.O. Box 10 01 64, 07701 Jena, Germany.
Isotopes Environ Health Stud. 2003 Jun;39(2):85-104. doi: 10.1080/1025601031000108642.
Oxygen is a globally important element, in inorganic compounds it is involved in key structural compounds of the earth, and it is providing functional groups for most organic compounds. Oxygen isotope ratio analyses on these compounds provide information on the oxygen sources and (formation) reactions in which the compound was involved. Therefore generally applicable analytical methods for the delta18O determination are highly desirable. After a description of online high temperature "carbon reduction" methods for the conversion of oxygen in the compounds mentioned into CO and discussion of problems involved, especially in analysis of inorganic substances like carbonates and silicates, selected examples for the application of these carbon reduction methods will be presented. The well-known correlation of delta18O values of cellulose (in tree rings) to that of (leaf) water is used since the 1970's as climate indicator. The observed enrichment in 18O in cellulose by about 27% in comparison to leaf water is attributed to an oxygen equilibrium isotope effect between carbonyl groups and water. But not all carbohydrates show this "general"18O enrichment relative to water. By means of a recently published model a non-statistical oxygen isotope distribution in carbohydrates is postulated. Oxygen isotope discrimination has been recognized long ago as an important principle of authenticity evaluation in food and beverages. Though many basic mechanisms of isotope discrimination in nature are known, the corresponding application of data is often based only on empirical observations in this field. The fact that oxygen in natural organic plant material is derived from three sources (CO2, H2O, O2) with distinct differences in and that their incorporation by different reactions implies oxygen isotope effects of different sizes, is therefore of special importance, and it is attempted by means of individual isotopic increments of functional groups to predict global delta18O values of natural and nature-identical compounds. Vice versa delta18O values can also give hints on the elucidation of biosynthetic pathways.
氧是一种在全球范围内都很重要的元素，在无机化合物中，它参与了地球的关键结构化合物，并且为大多数有机化合物提供官能团。对这些化合物进行氧同位素比值分析，可以提供有关氧源以及该化合物所参与的（形成）反应的信息。因此，非常需要适用于一般情况的δ18O测定分析方法。在描述了用于将上述化合物中的氧转化为CO的在线高温“碳还原”方法，并讨论了所涉及的问题，特别是在分析碳酸盐和硅酸盐等无机物时遇到的问题之后，将给出这些碳还原方法应用的选定示例。自20世纪70年代以来，纤维素（在树木年轮中）的δ18O值与（叶片）水的δ18O值之间的著名相关性就被用作气候指标。与叶片水相比，纤维素中观察到的18O富集约27%，这归因于羰基与水之间的氧平衡同位素效应。但并非所有碳水化合物相对于水都显示出这种“一般”的18O富集。通过最近发表的一个模型，假定碳水化合物中存在非统计性的氧同位素分布。氧同位素分馏早就被认为是食品和饮料真实性评估的一个重要原则。尽管自然界中同位素分馏的许多基本机制是已知的，但该数据的相应应用通常仅基于该领域的经验观察。天然有机植物材料中的氧来自三个来源（CO2、H2O、O2），它们之间存在明显差异，并且它们通过不同反应的掺入意味着不同大小的氧同位素效应，因此这一点特别重要，并且试图通过官能团的个别同位素增量来预测天然和天然等同化合物的全球δ18O值。反之，δ18O值也可以为阐明生物合成途径提供线索。
