微量磷灰石中磷酸根氧同位素分析方法

Analytical Method for δ^(18)O of Phosphate in Trace Apatite

生物磷灰石壳体的磷酸根氧同位素组成是重建古温度理想指标之一,在古环境研究中具有重要意义.针对牙形石等磷灰石量极少的情况,稳定可靠的前处理方法是分析其δ^(18)O_(PO4)的重要保障,目前仅有少数国外实验室已建立了相关提取分析方法.结合这些方法的优缺点对分析步骤进行改进优化,建立了微量磷灰石的磷酸根氧同位素分析方法,通过硝酸消解磷灰石并除去非磷酸根氧,利用KF溶液沉淀法分离Ca^(2+),采用氨缓冲溶液形式调节pH,并加入AgNO_3溶液以氨挥发法将PO43-转化成Ag_3PO_4结晶分离,气体稳定同位素质谱仪在线测定Ag_3PO_4氧同位素组成.结果表明,方法全流程未产生明显的氧同位素分馏,样品最低仅需0.2mg,标准偏差小于0.2‰(1σ),与目前国际报道的分析精度一致.

The oxygen isotope composition of phosphate(δ^18OPO4)in bioapatite plays a significant role in paleo-environmental research as one of the ideal proxies for paleo-temperature reconstruction.However,for trace bioapatite(e.g.,conodonts),a reliable pre-treatment technology is quite important and difficult for its δ^18OPO4 analysis,resulting in analytical technique established only in several overseas laboratories.Here we combine the advantages of those methods and present a protocol on the analysis of δ^18OPO4 as Ag3PO4 for bioapatite of total sample size as small as 0.2 mg using a thermal conversion elemental analyzer(TC/EA)coupled to a continuous flow isotope ratio mass spectrometer(CF-IRMS)via a helium stream.Ag3PO4 is precipitated by NH3 buffer method after apatite being dissolved with nitric acid,Ca^2+being removed with KF solution and the solution being neutralized with ammonia buffer solution.The results indicate that analysis of δ^18OPO4 maintains an external precision of±0.2‰(1σ),meeting the international analytical standards.This method for analyzing δ18OPO4 of phosphate extracted from bioapatite is robust to be used to reconstruct paleo-temperature.