USP minimum sample weight

The United States Pharmacopeia (USP) is the American counterpart to the German pharmacopeia and is used by many companies in Germany as a guideline.

The requirements of the USP of balances are recorded in two chapters:

  • Chapter 41 is binding and includes requirements on:
    • Repeatability / standard deviation of 10 measurements
      With a safety factor of 2, this must not exceed 0.1% of the initial weight. As a rule, the repeatability is unchangeable over the weighing range, so the relative error increases as the initial weight decreases. This result in the smallest weight that can still be weighed in correctly.
    • Accuracy / sensitivity (0.1% of a test weight> 5% max)
  • Chapter 1251 is not binding and contains recommendations to the installation site also proposals for the regular (for example annual) testing of balances in a "Performance Qualification" (PQ). This includes more tests and acceptance criteria for:
    • Eccentric load
    • Linearity
    This additional annual audits may be covered with a DAkkS calibration.

Compared to the minimum weight as an annex to  the DAkkS calibration, the minimum weight is only repeatability considered according to USP. In a DAkkS calibration certificate parameters such as eccentric load or linearity flow into the measurement uncertainty in use. However, they have only a slight impact with small weights.