In the Pharmacopeial Forum of the American pharmacopoeia USP of July 2007, the drafts for two General Chapters that are to be revised were published:

• <41> Weights and Balances

• <1251> Weighing on an Analytical Balance

<41> Weights and Balances

Here some important points from this draft:

The performance of the balance is assessed by means of three tests:

1. The repeatability of the measurements must be smaller than 0.1 %.

2. The accuracy (verification through certified OIML or ASTM weights) must be better than 0.1 % (new!).

3. Short weight check (new!).

In determining the repeatability, the hitherto used expansion factor k=3 is now replaced by an expansion factor k=2. As a direct consequence of this, the minimum sample weight for the quality-relevant weighings affected by USP <41> is reduced by one third.

The emphasis of the new draft is on the routine operation of the balance: Typically, repeatability and accuracy are assessed before the balance is put into operation (e.g. during IQ, OQ, PQ) and afterwards periodically, in accordance with the effective SOPs. Usually, a weight check with internal or external check weights is conducted on every day on which the balance is used or in other appropriate intervals defined by the laboratory in SOPs.

<1251> Weighing on an Analytical Balance
 

The draft for this General Chapter was harmonised with the new proposal for Chapter USP <41>. The formerly effective General Chapter USP <1251> should be deleted entirely and replaced by a completely new text.

The new draft includes among others the following sub-topics:

• Installation
  (Temperature and humidity controlled room, minimisation of vibrations, etc.)

• Qualification and routine tests
  (Periodic tests for evaluating the performance, like e.g. eccentricity or reproducibility, furthermore daily short tests - or short tests defined in other intervals - conducted with internal or external check-weights)

• Operation of the analytical balance (minimum weight requirements)

• Selecting weights for external tests

• Buoyancy correction (new!)

Here, attention should be paid to the fact that General Chapter USP <41> is mandatory for quality-relevant tests within the framework of USP's scope of application, whereas the Chapter USP <1251> merely represents a recommendation and gives additional pieces of advice not mentioned in Chapter USP <41>.

The deadline for commenting both of the new drafts was 15 October 2007. It is to be expected that revised drafts for the two new chapters will be published in the Pharmacopeial Forum in the first quarter of 2008

Author:
Dr Günter Brendelberger
On behalf of the European Compliance Academy
With kind assistance from Dr Klaus Fritsch
Mettler Toledo AG, Switzerland