GasBenchⅡ顶空瓶内空气背景对<100μg碳酸盐中碳氧同位素在线测定的影响及校正方法初探  

Influence of the Air Background in GasBench Ⅱ Vials on the Measurements of C and O Isotopes in Carbonates and a Preliminary Study on Blank Correction Strategy

作　　者：杜广鹏[1] 王旭[2] 张福松[3] 

机构地区：[1]上海建桥学院,上海201319 [2]中国科学院新生代地质与环境重点实验室中国科学院地质与地球物理研究所,北京100029 [3]中国科学院地质与地球物理研究所稳定同位素实验室,北京100029

出　　处：《岩矿测试》2010年第6期631-638,共8页Rock and Mineral Analysis

基　　金：国家自然科学基金资助(40672113);中国科学院地质与地球物理研究所实验创新基金资助(ZC0904)

摘　　要：较为系统地研究了在特定排空时间下GasBenchⅡ顶空瓶内背景CO2的量和同位素组成变化,并检查了该空白CO2组分对碳酸盐C、O同位素在线测定的影响。结果发现,由于排空时间较短所导致的顶空瓶内剩余的空气CO2或由于排空方法不当所导致的外部空气少量回流都会对小样品量（〈100μg）碳酸盐C、O同位素测定结果产生显著影响。其影响程度取决于空白CO2的量和空白CO2与碳酸盐样品之间C、O同位素的差别大小。由此,对小样品量碳酸盐C、O同位素的测定结果进行了空白校正。当碳酸盐样品质量在20－100μg,校正后δ^13C和δ^18O值的标准偏差分别小于0.12‰和0.13‰,这证明了该空白校正方法的可行性。由于顶空瓶中空白CO2的量很小,所以对痕量CO2的量、δ^13C和δ^18O测定值的测定会存在一定波动,这对碳酸盐δ^13C和δ^18O校正值产生小于0.2‰的不确定度。采用准确测定的实验室空气CO2的δ^13C和δ^18O值则会大大减少该不确定度的影响。In this study, the amounts and isotopic compositions of the blank CO2 remaining in GasBench Ⅱ vials after specific time of flushing was characterized and its influence on the measured δ^13C and δ^18 O values of carbonates was examined. Results show that the blank CO2 remaining in the vials due to either incomplete removal of air caused by short time of flushing or an input from an inherent source would significantly influence the measured C and O isotopic compositions for small-sized of carbonate samples （ e.g. 〈 100 g）. The extent of this influence depends on the amount of blank CO2 and the isotopic differences of O and C in the blank CO2 and in the carbonate samples. Therefore, blank corrections to the measured δ^13C and δ^18 O values in carbonate samples were performed, especially for the small size of samples. When carbonate sample weight is are 20 - 100 μg, the corrected δ^13C and δ^18 O values have an overall precision of 〈0.12‰ and 〈0.13‰, respectively. This verifies the practicability of the described blank correction strategy. Because there is a variation in the measurements of trace amount of blank CO2 in remained vials and δ^13C and δ^18 O of blank CO2 , it results in a 〈 0.2%e uncertainty in corrected δ^13C and δ^18 O values for small-sized of carbonate samples. The uncertainty will be greatly reduced if precise measurement values of δ^13C and δ^18 O from CO2 in lab air were used for blank correction.

关 键 词：碳同位素 氧同位素 GasBenchⅡ 小样品量 碳酸盐 空白校正 

分 类 号：O628.21[理学—有机化学] O613.3[理学—化学]