乙酸铵交换法测定土壤阳离子交换量的不确定度评定研究

Uncertainty in Determining of Cation Exchange Capacity in Soil Samples by Ammonium Acetate Exchange Method

采用乙酸铵交换法测定土壤阳离子交换量,并分析了测量过程中不确定度的来源:样品和标准物质的称量,容量瓶、移液管和滴定管的体积,以及测量的重复性等。在此基础上对各不确定度分量进行评定,并计算得到合成不确定度和扩展不确定度。最后提出了在测定过程中减小不确定度的有效途径,认为乙酸铵交换法测定土壤阳离子交换量的结果不确定度主要来源于重复性测定,增加测量次数可以减小重复性的不确定度,从而降低测定不确定度。当土壤中阳离子交换量为22.5 cmol(+)/kg时,扩展不确定度为1.0 cmol(+)/kg,置信水平为95%。

The cation exchange capacity( CEC) in soil samples was determined by ammonium acetate exchange method.The results showed that the main factors that affected the determination results of CEC were as follows:weighting of soil samples and reference materials, volume of volumetric flask, pipette and burette, measurement repeatability, etc.Based on this, the uncer-tainty of measurement was evaluated and synthetic uncertainty and expanded uncertainty were calculated.Finally, the solving methods to improve the accuracy of CEC analysis were put forward.Results show that the measurement repeatability was the main influencing factors of uncertainty in the method.And increasing the number of measurements could reduce the uncertainty of re-peatability.When the CEC in soil samples was 22.5 cmol( +)/kg, the expanded detection uncertainty was 1.0 cmol( +)/kg with the certainty degree was 95%.