Dear all,
Do you know if there is any official standard or guideline specifying the acceptable limits of the analytical balance uncertainty?
Try USP chapters 41 and 1251.
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Please see the attachments of USP and WHO Guidelines .
Simply the analytical or Micro analytical balance should pass the Uncertainity of minimum weight(lowest weight that can measure accurately) should be verified.
(3x sd)/weight taken<0.001
sd= standard deviation.
For eg: take 50 mg of standard weight and measure the weight 10 times, calculate the sd.
and calculate the uncertainity using the formula.
This is nothing but 0.10% accuracy.
Usually analytical balance should be used from 50 mg onwards to 80% of the balance higher range.
Below 50 mg the this is not suitable. because the nearest weight for 50 mg is 20 mg.
Uncertainity fails for 20 mg weight using analytical balance.
Next available weight is 50 mg, It passess the uncertainity requirement.
Hence below 50 mg, analytical balance is not suitable, this is clearly written in WHO Guideline, which is attached.
For your information.
Regards,
Bujji Kanchi.
+91-9676749937
Hi,
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you please refer usp<41> general chapter
Pl. see the attached file. I hope it will be useful for you.
Dr.Pradeep Nagalkar
Balance Good Weighing Practices.pdf (509.1 KB)