Implementing the Revisions to the EP Chapters on Weighing

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Quality Management Service (QMS) Blog series 1


The EP Chapter 2.1.7, updated on 1st of July -2021, contains new specifications for weighing, such as calibration and testing of balances.


European Pharmacopoeia Chapter 2.1.7 applies to the analytical balances only for the use of weighing for analysis. Also,  this chapter is effective and mandatory to be followed by the manufacturer of Pharmaceutical Drug substances & Drug Products from the 1st of January 2022. Since USP chapter 41 and Ph. Eur. 2.1.7 are not harmonised Ph. Eur. 2.1.7 has slightly different requirements for the precision and accuracy test users have to be aware of.


These revisions aim to ensure describes requirements on balances used for analytical procedures and performance checks like 

  1. Periodic calibration including measurement uncertainty
  2. Performance checks between calibration intervals to assess:

     b.1 Accuracy

     b.2 Precision 


Let’s dive into more details! The laboratory balances required to comply with Ph. Eur. 2.1.7 are described as below.

Calibration

Calibration is part of the balance qualification to ensure compliance with pre-defined requirements and is usually performed by a competent agency or In-House, by a well-trained person. 

The calibration results are documented in a calibration Report / Certificate and must be carried out periodically (as defined by the users’ QMS).

Performance:

Performance tests are carried out to evaluate the random and systematic errors of the balance and consist of a repeatability test (the ‘random’ error or ‘precision’ of the balance) and a sensitivity test (the ‘systematic’ error or ‘accuracy’ of the balance). Again, these are carried out periodically as defined by the users’ QMS.

Sensitivity

The sensitivity of the analytical balance is always impacting on Accuracy of the balance very significantly. This increases in a linear manner proportionate to the applied load. Random error is dominant at the lower end of the measuring range.  

It is performed with a single standard weight of between 5% and 100% of the capacity of the balance.

Acceptance criteria: 

Ph.Eur. Chapter 2.1.7

USP 41

0.05%

0.10%


Repeatability

The repeatability requirement defines a specific test with an acceptance criterion that the balance should meet. 

A weight no less than 0.1g or more than 5% of the capacity of the balance is added and removed 10 times and the standard deviation (s) is calculated. The minimum weight is defined as equalling 2000 x s. If is less than 0.41 x d (d is the readability or scale interval of the balance) the minimum weight is calculated as 820 x d according to both Ph. Eur. Chapter 2.1.7 and USP Chapter 41.

For Example,

Readability or scale interval of balance (d)

User is getting value of standard deviation(s) 

As per Ph. Eur requirement 0.41xd = 

In that case value of s (0.00003) is lower than value of 0.41xd (0.000041), hence Minimum weight calculation is 

0.0001

0.00003

0.41x0.0001 = 0.000041

2000x0.000041= 0.0820 gm(82mg)        


The ‘minimum weight’ is the smallest net sample mass that can be weighed on the balance while still satisfying this acceptance criterion. This should not be confused with the ‘smallest net weight’, which is the smallest quantity that END USER need to weigh on the balance daily.