USP Chapters 41 and 1251 Revised: What Analysts Need to Know

As part of our coverage of Analytica USA, Spectroscopy sat down with Ian Ciesniewski, technical director at Mettler Toledo, to discuss the latest changes made to the United States Pharmacopeia (USP) Chapters 41 and 1251. In the below interview segment, Ciesniewski discusses how the recent changes to these two chapters will impact organizations.

Spectroscopy: Can you discuss the specific changes that were made in USP General Chapter 1251 (Weighing on an Analytical Balance) and explain how these changes will impact organizations?

Ian Ciesniewski: Chapter 1251 is a nice, informational chapter rather than an auditable chapter. It has everything within it to get better performance from your balance. The chapter tells you the kind of external influences that affect the balance and also explains the testing that's required for Chapter 41 and how to go about it. There's plenty of good tips and tricks for in practice; it's a very good document for the industry to give out to the technicians and analysts so that they understand what they do and how that affects the balance.

So, 1251 has always been a much bigger chapter, because obviously it covers the whole science of weighing. But there's some good points that have been in it for a long time, but now the team has done a great job of clarifying some of these points. For example, it talks about using the safety factor that I mentioned just now for 41 in saying that for your own chosen minimum weight, you want to put the smallest weight on balance, which is a representation of the repeatability. The best of the repeatability, the smaller the minimum weight.

It also talks about your own chosen net sample weight, so your own smallest net weight should be bigger than the calculated minimum weight for the balance, so that you've always got that safety factor that I mentioned earlier. It talks about monitoring that safety factor during the lifetime of the balance, recognizing the balance’s age.

Also, for the first time, Chapter 1251 talks about the fact that you don't have to do a balance weight checks on a daily basis. The frequency is dictated by the performance capability of the balance in your lab. We call that the weight system, by the way, and that's just another Toledo terminology. And it also talks about, you know, understanding the robustness of your own testing system. In other words, the more robust your testing system, the better that you can control those numbers you're going to find.

This interview segment with Ciesniewski is part of our conversation with him. You can view all our coverage of Analytica USA here.

Reference

1. Analytica USA, Speakers: Ian Ciesniewski. Analytica USA. Available at: https://aus2025.mapyourshow.com/8_0/sessions/speaker-details.cfm?speakerid=28 (accessed 2025-09-24).