海洋沉积物有机碳和稳定氮同位素分析的前处理影响

海洋沉积物中的有机碳和稳定氮同位素为海洋古环境和碳氮循环提供了大量信息,然而不同的前处理方法对有机碳和稳定氮同位素测定结果的准确性产生不同程度的影响.笔者通过大量条件实验,分析了前处理过程中影响结果准确性的可能因素.①器皿材质:使用聚丙烯和玻璃离心管进行酸处理所得样品的δ13C和δ15N基本无差别.②干燥方式:样品经热烘干燥会导致样品中轻碳组分和易挥发组分的逸散,引起样品中δ13C的分馏.鲜样和酸处理后样均采用热烘干燥会引起样品中δ15N发生明显分馏.③驱酸方式和洗酸程度:水洗造成溶解性有机碳和氮的损失,致使δ13C和δ15N值较真实值偏正,但酸蒸法不能保证氯离子的有效驱除.洗至中性后的洗酸次数对δ13C影响甚小,但会导致δ15N继续偏正.全程采用冷冻干燥,选用PP离心管作为主要酸处理水洗和干燥的器皿,具有很好的重复性,可获得较理想、准确的δ13C和δ15N测试数值.

The Research on Sample-pretreatment of Organic Carbon and Stable Nitrogen Isotopes in Marine Sediments

The organic carbon and nitrogen isotopes in marine sediments provide a lot of information about marine paleoenvironmental and carbon and nitrogen cycles. However, different pretreatment methods have different impacts on the accuracy of the results of organic carbon and nitrogen isotope. This paper analyzed the factors affecting the pretreatment process on the basis of a great many condition tests. (1) Acid treatment Containers Material: The organic carbon and nitrogen isotope values of acid treatment with polypropylene and glass centrifugal tubes make no difference. (2) Drying methods: The sample δ13C will be fractionationed for the escape of light carbon and volatile components caused by heat-drying. The sample δ15N will be fractionationed caused by the fresh and acid-treated samples heat-dried. (3) The drive acid method and wash acid times: Dissolved organic carbon and nitrogen will be loss caused by washing, resulting in δ13C and δ15N values more partial than the true ones. Meanwhile, steaming acid can not get rid of chloride ions effectively. The effect of acid wash times on δ13C is very small, but it will result in δ15N partial. In short, using of freeze-drying, the choice of PP centrifugal tube as the main acid treatment washing and drying vessels, with good reproducibility, get more satisfactory and accurate test δ13C and δ15N values.