Compound-specific carbon isotope analysis of low-molecular organic acids and its application to geochemical samples

低分子有机酸的化合物特异性碳同位素分析及其在地球化学样品中的应用

基本信息

批准号：
09554030
负责人：
NARAOKA Hiroshi
金额：
$ 6.08万
依托单位：
TOKYO METROPOLITAN UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1997
资助国家：
日本
起止时间：
1997 至 1999
项目状态：
已结题

项目摘要

Carbon isotopic compositions of individual low-molecular carboxylic acids such as acetic acid and oxalic acid were measured on sub-nano mol level using gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS). While free monocarboxylic acids are hard to oxidaze to COィイD22ィエD2 quantatively in a micro volume furnace, decyl ester derivatives of the acids are easier to convert to COィイD22ィエD2. Also the dicarboxylic acids were derivatized to dibutyl esters for the GC/C/IRMS measurement. Using internal isotopic standards of n-alkanes, analytical precision was within ±0.3‰. Isotopic mass balance calculation shows that the corrected analytical precisions are 2-3‰ for the free acids.Carbon isotopic compositions of individual organic acids in oil-field waters from Sarukawa Oil Field (Funakawa Formation, Miocene) in the northern Japan. The δィイD113ィエD1C values of acetic acid and propanoic acid range widely from -61 to -23‰ (relative to PDB) and -from -51 to -28‰, respectively. The low-molecular acids are more depleted in ィイD113ィエD1C than the bulk crude oil (ca. -22‰) produced from the same formation. The δィイD113ィエD1C values of acetic acid correlate well (rィイD12ィエD1=0.94) with those of propanoic acid (n=7 with one exception). Isotopically heavy acids tend to be observed in higher temperature water. In addition we conducted hydrous pyrolysis of kerogen purified from the same formation. The isotopic composition of acetic acid and propanoic acid produced by the pyrolysis experiment is plotted on the correlation that is observed in natural samples. These results suggest that the low-molecular monocarboxylic acids are produced by cracking of kerogen.

使用气相色谱/燃烧/同位素比质谱 (GC/C/IRMS) 在亚纳米摩尔水平上测量各种低分子羧酸（例如乙酸和草酸）的碳同位素组成，而游离单羧酸则很难测量。在微量炉中定量氧化为CO22D2，酸的癸酯衍生物更容易转化为CO2D22D2。并且将二羧酸衍生为二丁酯用于GC/C/IRMS测量，使用正构烷烃的内部同位素标准，分析精度在±0.3‰之内。游离酸为2-3‰。油田水中各种有机酸的碳同位素组成日本北部的猿川油田（船川组，中新世），D113 中的低分子酸含量比散装原油（约 28%）更贫乏。 -22‰），乙酸的 δD113D1C 值与丙酸的 δD113D1C 值（rD12D1=0.94）有很好的相关性（n=7，但有一个例外）往往在较高温度的水中观察到。此外，我们对从同一地层提纯的干酪根进行了含水热解，得到了乙酸和丙酸的同位素组成。将热解实验产生的酸与在天然样品中观察到的相关性绘制出来。这些结果表明低分子一元羧酸是通过干酪根裂解产生的。