Margolis S A
Analytical Chemistry Division, National Institutes of Standards and Technology, Gaithersburg, Maryland 20899, USA.
Anal Chem. 1997 Dec 1;69(23):4864-71. doi: 10.1021/ac9704826.
The sources of systematic bias in the measurement of moisture by the volumetric and coulometric Karl Fischer methods were assessed. Using water-saturated octanol as a moisture standard, the measurement accuracy of five coulometric instruments was evaluated. Six possible sources of systematic bias were examined: accuracy of the moisture standard, nonadjustable instrumental bias, operator-adjustable instrumental bias, solvent composition, cell design, and sample composition. The published water content of water-saturated octanol was confirmed by the method of standard additions. The nonadjustable instrumental bias consisted of two types, one that was variable and was observed at water levels below 200 micrograms of water, and one that represented a constant percentage of the total water over the tested range from 40 to 400 micrograms of water. The adjustable instrumental parameters, if set incorrectly, may cause a small but significant negative bias (< 7%). Solvent composition as a function of both solvent type and titration vessel design can introduce a negative bias of up to 10%. Finally, the nature of the sample introduces a negative bias as demonstrated by the results obtained from titrating water in four different oil samples. Under optimum conditions, different amounts of water were measured in each oil using different Karl Fischer titration procedures and five different instruments.
评估了容量法和库仑法卡尔费休水分测定中系统偏差的来源。以水饱和辛醇作为水分标准品，评估了五台库仑仪的测量准确性。研究了六种可能的系统偏差来源：水分标准品的准确性、仪器不可调偏差、仪器可由操作人员调整的偏差、溶剂组成、电解池设计和样品组成。通过标准加入法证实了已公布的水饱和辛醇的含水量。仪器不可调偏差有两种类型，一种是可变的，在水含量低于200微克时观察到，另一种在40至400微克水的测试范围内占总水量的恒定百分比。仪器的可调参数如果设置不正确，可能会导致小但显著的负偏差（<7%）。作为溶剂类型和滴定容器设计函数的溶剂组成可引入高达10%的负偏差。最后，如对四种不同油样中的水进行滴定所得到的结果所示，样品的性质会引入负偏差。在最佳条件下，使用不同的卡尔费休滴定程序和五台不同仪器对每种油中的不同水量进行了测量。
