Hi all new to this company. Just handed our approved SOP for "Use, Verification, and Maintenance of balances in QC" Also given USP docs <41> Weights and Balances and <1251> Weighing on an Analytical Balance.
I am scratching my head over <41> "Unless otherwise specified, when substances are to be "accurately weighted" for Assay, the Weighing is to be performed with a weighing device whose measurement uncertainity (random + systomatic 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 devided by the ampount weight, does not exceed 0.001. The question is "weighing device" is that the analytical balance or the actual weights (class 1.1 or 2 or 3)? Does this paragraph only describe how to choose the class of weights and not to the analytical balance with regards to tolerance of the weighted number? Am I totally off the mark? Our company's SOP has us measure a weight 10 times, get a Standard Dev mul by 3 and devide by weight and then compare that number to accept <0.001. They call that the "Balance measurement of uncertainty" The balance acceptance criteria is the mean +/- 0.001% (yes %) of the mean. Our balances are failing at the 10gram weight (passes Std Dev formula <0.001) but fails the mean +/- value. Their answer is to get a bigger weight (100g) and then the mean +/- value passes. The justification is we choose a weight that is in the middle of the balance range as oppoised to the weight we typically measure around (10g).
I know I am wordy; but, appriciate any help.
The other question comes from <1251> page 2 check for drift. "The check for drift at the most sensitive position will show whether a problem exists; the variation in the observed weight foes not exceed +/- 0.2mg. They give an example of a 20g weight. The question is is the +/- 0.2mg tolerance apply to the entire range of the analytical balance, (i.e, 0 - 220g)? Our company'