原文由 cubis-victor(cubis-victor) 发表:
如果这个误差不重复呢?是不是取平均值?
原文由 edwardli(edwardli) 发表:原文由 drugmen(drugmen) 发表:
“10次称样结果的标准偏差”
这个如何来的?称量100次?
还有,这里的砝码应该选用在砝码组中,与最大量程的40%重量最接近的那个,
例如:对Mettler Toledo 的XS205型天平进行最小称量值测定,在0.1mg精度时量程为0~220g,则其最大量程的40%为88g,应该选用100g的砝码进行测定。
而在0.01mg精度时,量程为0~81g,则其最大量程的40%为32g,则应选择20g的砝码进行测定。
原文由 仰望天空的鱼(zc3205) 发表:
Pharmacopeial tests and assays require balances that vary in capacity, sensitivity, and reproducibility. Unless otherwise specified, when substances are to be “accurately weighed” for Assay, the weighing is to be performed with a weighing device whose measurement uncertainty (random plus systematic error) does not exceed 0.1% of the reading. Measurement uncertainty is satisfactory if three times the standard deviation of not less than ten replicate weighings divided by the amount weighed, does not exceed 0.001. Unless otherwise specified, for titrimetric limits tests, the weighing shall be performed to provide the number of significant figures in the weight of the analyte that corresponds to the number of significant figures in the concentration of the titrant.这是USP(41)的一段原话,这段话告诉我们天平的最小称样量为3000*10次称样结果的标准偏差(我们这里的最小称样量是以10mg砝码计算出来的)