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Thursday, August 11, 2011

USP Minimum Sample Weight

Minimum sample weight is defined as the minimum sample quantity required by a balance or scale to obtain a reliable result, taking into account factors such as measurement uncertainty. In the pharmaceutical industry, the United States Pharmacopoeia (USP) is widely recognized as the official authority that prescribes the requirements for determining minimum sample weight.

According to USP Chapter <41> Weights and Balances i, measurement uncertainty should satisfy the following requirements:
  1. The measurement uncertainty of a balance or scale does not exceed 0.1% of the reading.
  2. Three times the standard deviation ii, as determined by at least 10 replicate weighings, does not exceed 0.001 (0.1%) when divided by the amount weighed.
The conditions above can be expressed using the following equations:

Resolution
Model
Capacity
Repeatability (σ)
Measurement Uncertainty (3σ)
Minimum Sample Weight
0.01mgGH-20251g (Fine range)0.02mg0.06mg60mg
GR-20242g (Fine range)
0.1mgGH-200220g0.1mg0.3mg300mg
GR-200210g
0.001gGX-200210g0.001g0.003g3g
0.01gGX-20002100g0.01g0.03g30g

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