预处理过程对不同类型样品中有机碳含量和稳定碳同位素测定的影响

Influences of Pretreatment Procedures on Determination of Total Organic Carbon and Stable Carbon Isotope in Different Samples

总有机碳（TOC）是土壤、沉积物以及降尘等固体样品的重要指标,对其含量和稳定碳同位素（#13 C）进行准确测定具有重要的科学意义。在测定过程中,样品的预处理方法可能会对测定值产生一定影响。本文主要从酸处理方式、干燥方式等方面研究了预处理方法对不同类型样品的TOC含量和#13 C值测定的影响。其中酸处理方式选取了盐酸酸化/分离、红外碳硫坩埚、Ag杯直接酸化等三种方式,干燥方式包括加热干燥和真空冷冻干燥等。研究结果显示：酸处理方式对TOC含量测定的影响很大,Ag杯和盐酸酸化/分离未去除残留酸液两组实验所测得TOC含量明显大于其他组,其中降尘样品TOC的损失量可达20%。这种明显的差异可能是样品酸处理过程中水溶性有机碳（DOC）的损失所造成的。对于#13 C测定来说,该两组实验所测得#13 C相对于其他组略微偏重,其中地表土壤样品偏重约为0.8‰~2‰。另外加热干燥和真空冷冻干燥方式测定的TOC含量和#13 C值没有明显的变化,表明了挥发性有机物（VOC）对本次实验所选用样品的有机碳分析影响甚微。综合来看,对于不同类型样品,特别是DOC含量高的样品,使用Ag杯的酸处理方式相对比盐酸酸化离心分离酸处理方式能更大限度的保留DOC,使TOC含量和#13 C值的测定较为准确可靠,同时操作起来也更加简便快捷。

As important properties of soils, sediments and atmospheric dust, it is very important to accurately quantify the total organic carbon （TOC） contents and stable carbon stable carbon isotope （δ13 C） in these samples. In fact, the pretreatment procedures may have certain impacts on the measured results of TOC and δ13 C. In this study, the influences of pretreatment procedures on the determination of TOC and δ13C in different samples were investigated by two ways： acid treatments and dry methods. The tested acid treatment procedure includes hydrochloric acidification/separation, infrared carbon and sulfur crucible, and in-situ Ag cup acidification. The tested drying method include heat drying and vacuum freeze drying. Results show that the acid treatment has important effects on the determination of TOC in different samples. The TOC values determined using methods of hydrochloric acidification/separation method but reserving residual acid and irrsitu Ag cup acidification are significantly higher than those of other groups, especially for the atmospheric dust sample which increased 20 % of TOC. These differences can he explained by the fact that dissolved organic carbons （DOC） are removed during the acid treatment process. The δ13C values determined with these two methods are slightly positive than those of other groups, especially for surface soil samples those increase around 0.8%-- 2%. However the drying method of heat drying and vacuum freeze drying does not have observable effects on the determination of TOC and δ13C in different samples, which may indicate that the influences of volatile organic carbon （VOC） on the determination of TOC and 813C in these tested samples are ignorable. In summary, the irrsitu Ag cup acidi- fication method has many advantages such as time saving, operation easy, and more accurate, thus it may be a good method to measure the TOC contents and δ13C in different samples, especially for the samples with high levels of DOC.