中文摘要：

本文给出了元素分析仪-同位素比值质谱（EA-Conflo-IRMS）联机系统的燃烧转化率随测量样品次数的变化规律，以及样品的氮、碳同位素测量值与其燃烧转化率的关系。在测量前356个样品时仪器的燃烧转化率几乎不变，测量接下来的127个样品时燃烧转化率逐渐递减，而最后65个样品的燃烧转化率保持在另一个显著降低的水平。当燃烧转化率显著降低时，还原管的填料被大量氧化，氧化管上部的氧化能力下降。尽管由于受多种因素的影响同位索测定值的变化表现出一定的复杂性，但是样品的氮、碳同位索值总体上随着燃烧转化率的降低而变负。为了校正仪器漂移的状态，采用反标定方法对EA-Conflo-IRMS联机系统在状态漂移时的CO2参考气同位索值进行了重新设定，并再次测量了几个标准样的碳同位索值，其结果的准确度在0．1‰以内且测量精度好于0．15‰。可见，定期通过反标定来消除燃烧转化率漂移对同位索值产生的影响是可行的。

英文摘要：

A clear picture of the changes in combustion transformation capability （CTC） of EA-Conflo-IRMS with the number of samples was measured and the relationship of measured nitrogen and carbon isotope ratios with their CTC were depicted by analysis of the data accumulated in the long time of work. The CTC displays little variation during a period of first 356 runs, followed by the degression of CTC for the subsequent 127 samples and the ensuing relatively lower level of CTC for next 65 runs. This marked decrease in CTC occurred when most Cu in reduction tube was oxidized and the oxidative ability of upper part of combustion tube declined. Moreover, the measured nitrogen and carbon isotope ratios tend to reduce with the declined CTC despite there are some complicated changes in the measured isotope ratios due to the influences of other factors. In order to normalize the shifted state of this machine, a reversed calibration was performed on the CO2 reference gases by some standards, determined when EA-Conflo-IRMS at its lowered CTC level, to give out the properly normalized ＆values, relative to which the carbon isotope ratios of some standards were measured again. The accuracy （less than 0. 1‰） and precision （better than 0.15‰） indicate the practicability of the above method.