大洋有孔虫碳、氧稳定同位素标准物质的研制

PREPARATION OF CARBON AND OXYGEN STABLE ISOTOPE REFERENCE MATERIAL FOR OCEANIC FORAMINIFERA

有孔虫氧、碳稳定同位素比值的微量测定是古海洋学研究的最基本手段之一，其中标准物质对获取高准确度数据起关键作用。测定表明，标准物质的氧同位素比值和有孔虫样品的氧同位素比值（δ１８ＯＶ－ＰＤＢ介于４．０‰～－３．０‰之间）越接近，则测出的样品值就越准确；反之，若相差越远，则测出的样品值系统误差就越大。国内现有的碳酸盐碳、氧同位素标准物质的氧同位素值与有孔虫相比都偏负，不适宜用作有孔虫的稳定同位素分析。鉴于此，我们选取云南大理地区的二叠系茅口组灰岩为候选样品，遵循现行的国家一级标准物质计量技术规范ＪＪＧ１００６－８６的要求，同时参照国际原子能委员会（ＩＡＥＡ）同类标准物质的研制方法，研制出ＧＳＳＩ－１碳酸盐碳、氧稳定同位素标准物质共计６ｋｇ，该标准物质的均匀性、稳定性良好，主要特性量值δ１３Ｃ、δ１８Ｏ的推荐值为：δ１３ＣＶ－ＰＤＢ（‰）＝３．４１，δ１８ＯＶ－ＰＤＢ（‰）＝－１．６１。

The micro quantity determination of carbon and oxygen isotope ratios of foraminifera is a fundamental technique of paleoceanographic study,in which reference materials play a key role in acquiring high quality data.Experiments show that the closer oxygen isotopic ratios of reference material to those of foraminifera samples(δ 18 O V PDB :4 0‰～-3 0‰)are,the more accurate the analytic data should be and vice versa.However,oxygen isotope values of current domestic carbon and oxygen isotope reference materials of carbonate are all too negative compared with foraminifera,hence they are not suitable for isotopic analysis of foraminifera.In view of this situation,we selected Permian Maokou Formation limestone from Dali,Yunnan Province as candidate sample and prepared a new carbon and oxygen isotope reference material of carbonate named as GSS 1 whose weight totalled 6kg.The preparation work followed the current national measure technical specification for primary reference materials JJG1006 86 and also referred to the preparation method of similar reference materials by IAEA.The homogeneity and stability of GSSI 1 were excellent.An intercomparison test by 8 laboratories yielded provisional certified values as following:δ 13 C=3 41‰;δ 18 O=-1 65‰ vs V PDB.GSSI 1 will satisfy the needs for stable isotope analysis of foraminifera since its δ 18 O value was within the range of δ 18 O values of foraminifera.The preparation of GSSI 1 also filled in the gaps that China lacked carbon and oxygen isotope reference materials of carbonate whose δ 18 O values were relatively positive.