At its 168th session (November 2020), the European Pharmacopoeia (Ph. Eur.) Commission adopted a new general chapter: Balances for analytical purposes (2.1.7). This new chapter is included in Supplement 10.6 of the Ph. Eur., published in July 2021.
This addition to section 2.1. Apparatus fills a long-standing gap by setting out clear requirements for a piece of equipment that is the cornerstone of every analytical procedure described in the Ph. Eur. Weighing is one of the most common but also most critical tasks in a laboratory, as even the smallest weighing error can propagate throughout the whole analysis, affecting the accuracy of reported results.
After a brief overview of the principles of balances and recommendations on their installation and use, including good practices for weighing vessels, the chapter provides detailed information on calibration and carrying out performance checks during routine use and between calibrations. These checks focus on two weighing parameters that most significantly affect balance performance, i.e. repeatability, which affects the precision of the balance, and sensitivity, which affects its accuracy. The result of the repeatability test described in the text can also be used to calculate the minimum weight of the balance. This is the smallest net mass of substance that can be weighed on the instrument while continuing to comply with the repeatability requirement, making it an important property that must be taken into account when using a balance in a laboratory setting.
This new general chapter complements existing guidelines for the use and qualification of balances published elsewhere. The principles outlined in it apply to all weighings performed as part of analytical procedures prescribed to establish compliance with a Ph. Eur. text. It is supplemented by the instructions related to “Quantities” given in the recently revised General Notices chapter, which is due to be published in Supplement 10.7 and which now includes a reference to this new chapter.