生活饮用水3M Petrifilm~(TM)菌落总数测试片法的不确定度评定

对3M PetrifilmTM菌落总数测试片法检测生活饮用水中菌落总数的测量结果进行了不确定度评定,评述了引起测量结果不确定度的主要因素,对样品稀释及方法精密度因素进行了详细评价,并对单一样品重复测量10次及30个样品每个样品平行测量2次的两种情况,分别进行了重复性标准偏差评价。结果显示:单一样品重复测量时,测量结果的不确定度主要由样品稀释和重复性标准偏差引起,扩展不确定度U95为20CFU/mL,k=2;多个样品每个样品平行测量2次时,测量结果的不确定度主要由重复性标准偏差引起,在95%的置信度时,扩展不确定度U(lgxj)为0.093,k=2.75。

Measurement uncertainty evaluation of 3M PetrifilmTM aerobic count plate method for drinking water

The aerobic plate count in drinking water was determined with 3M PetrifilmTM aerobic count plate,and their measurement uncertainties were evaluated in this study.Firstly,the main components of measurement uncertainty were discussed and analyzed.Then,two most important components,sample dilution and measurement precision were evaluated in detail.And for the precision,the authors evaluated two kinds of precision commonly used in routine work,the repeatability of 10 repeated measurements of single sample and those of double repeated measurements of thirty samples.Experimental results show the sample dilution affects the measurement uncertainty obviously for the case of single-sample test,and the standard deviation of repeated measurement is the most important source of uncertainty for that case and the case of multi-sample test.The expanded uncertainty U95 was 20 CFU/mL(k=2) for the former case and the expanded uncertainty U(■) was 0.093(k=2.75) for the latter when the degree of confidence is 95%.