燃烧氧化-非分散红外吸收总有机碳分析仪测定海水DOC的不确定度分析

Evaluation of uncertainty in measurement of dissolved organic carbon in seawater using high temperature combustion-nondispersive infrared absorption TOC analyzer

采用实验测定和误差分析的方法,对燃烧氧化-非分散红外吸收总有机碳分析仪vario TOC cube测定海水DOC含量的不确定度进行了分析,对导致测定结果不确定度的各分量进行了量化估算。结果表明,其测定结果的不确定度主要来源于四个方面,即样品重复性测量、标准曲线拟合、标准溶液配制(包括称量、定容、移液产生的不确定度,标准物质纯度和相对原子质量产生的不确定度)及测量仪器本身,相对标准不确定度分量分别为0.016、0.018、0.0086、0.0079。标准曲线拟合与样品重复性测量是影响海水DOC测定不确定度的主要因素,但标准溶液配制和测量仪器所引起的不确定度亦不可忽略。对实际海水DOC浓度为1.20 mg/L的样品分析,合成以上四种不确定度分量得到DOC测定结果的标准不确定度为0.21 mg/L。按照正态分布,取扩展因子k=2,则扩展不确定度为0.07 mg/L,此海水样品中DOC含量的测定结果应为(1.20±0.07)mg/L(k=2)。

The uncertainty of dissolved organic carbon （DOC） content in seawater determined by combustion oxi-dation-non-dispersive infrared absorption vario TOC cube was evaluated using experimental determination and er-ror analysis methods, then the individual uncertainty arising from each source was calculated. The results showed that the uncertainty was mainly from four aspects： repeated experiment of sample, fitting for the standard curve, preparation for the standard solution （including the uncertainty resulted from weighing, volume determination, translation, purity of reference material and relative atomic mass） and measuring instrument. The uncertainty values were 0.016, 0.018, 0.0086, 0.0079, respectively. The main factors influencing the uncertainty of DOC determination in seawater were fitting for the standard curve and repeated experiment of samples, but the uncertainty caused by preparation for the standard solution and measuring instrument can’t be ignored. In this study, the actual concentra-tion of DOC sample was 1.20 mg/L and standard uncertainty of the result was 0.21 mg/L. According to the normal distribution, the expanded uncertainty was 0.07 mg/L when the expansion factor k=2.The final result of DOC con-tent in seawater should be （1.20±0.07） mg/L （k=2）.