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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δ13C和δ18O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、δ13C和δ18O测定值的测定会存在一定波动,这对碳酸盐δ13C和δ18O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δ13C和δ18O值则会大大减少该不确定度的影响。
The background CO 2 content and isotopic compositions of GasBench II headspace vials were studied systematically under a specific emptying time and the effects of the blank CO 2 components on the online determination of C and O isotopes of carbonates were examined. It was found that small samples (<100 μg) of carbonate C, O isotopic determinations (<100 μg) of residual air CO2 in headspace bottles due to short emptying times or small amounts of external air backflow due to inadequate emptying methods Have a significant impact. The degree of influence depends on the amount of blank CO2 and the difference in C and O isotopes between blank CO2 and carbonate samples. As a result, blank calibration was performed on the measurement results of the carbonate C and O isotopes of small samples. When the mass of carbonate sample is in the range of 20 ~ 100μg, the standard deviation of δ13C and δ18O after calibration is less than 0.12 ‰ and 0.13 ‰ respectively, which proves the feasibility of the blank calibration method. Due to the small amount of blank CO2 in headspace bottles, the determination of the δ13C and δ18O values for the amount of trace CO2 fluctuates somewhat, creating an uncertainty of less than 0.2 ‰ for carbonate δ13C and δ18O calibrations . The accurate determination of the δ13C and δ18O values of laboratory air CO2 greatly reduces the impact of this uncertainty.