USP & Minimum Sample Weight A&D

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:

The measurement uncertainty of a balance or scale does not exceed 0.1% of the reading.

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:

Now, given that the standard deviation based on 10 or more replicate weighings is the repeatability of a balance,

is obtained.

● Examples of Minimum Sample Weights ⁱⁱⁱ

Resolution	Model	Capacity	Repeatability (σ)	Measurement Uncertainty (3σ)	Minimum Sample Weight
0.001 mg	BM-20	22 g	2.5 μg (for 1 g)	7.5 μg	7.5 mg
0.01 mg	BM-252	250 g	0.03 mg (for 100 g)	0.09 mg	90 mg
	GH-202	51 g (Fine range)	0.02 mg	0.06 mg	60 mg
	GR-202	42 g (Fine range)	0.02 mg	0.06 mg	60 mg
0.1 mg	BM-500	520 g	0.2 mg	0.6 mg	600 mg
	GH-200	220 g	0.1 mg	0.3 mg	300 mg
	GR-200	210 g	0.1 mg	0.3 mg	300 mg
0.001 g	GX-200	210 g	0.001 g	0.003 g	3 g
0.01 g	GX-2000	2100 g	0.01 g	0.03 g	30 g

The information presented here is for reference purposes only. Please refer to the latest guidelines issued by the USP when conducting actual tests.

For an explanation of standard deviation, see　here

The balances are presumed to have been properly calibrated and operate in a favorable environment according to specification. Repeatability is influenced by environmental conditions as well as the balance’s settings. For purposes of accuracy, it is therefore necessary to calculate the minimum sample weight on location during actual tests.

<< Return 　