Does the revised USP Chapter 41 on "Balances" apply to all weighing instruments used in our facility?
It applies only to balances that are used to perform “accurate weighing."
"Accurate weighing" needs to be defined individually. It is recommended to link this definition to the actual accuracy required by your corresponding standard operating procedure (SOP); for example, if an SOP requires you to weigh x mg with an accuracy of ±0.1%, this refers to accurate weighing. If you weigh in order to prepare buffers, this may not necessarily involve accurate weighing.
No specific testing interval has been defined. Sartorius therefore recommends having these USP tests performed along with service and/or maintenance at regular intervals, at least once a year.
Sartorius recommends that you use one weight that is nearly half of the maximum capacity of your balance.
It is likely that the FDA will check additional balances during their visits. If a mandatory chapter in the USP, such as Chapter 41, has changed after such a long period of time, you can expect the FDA to include such aspects in audits.
Not necessarily. As the new USP Chapter 41 requirements do not differ very much from those of the former chapter, you can expect that your balance will meet these new ones. It is even possible that you are allowed to weigh even smaller amounts under the new regulations.
Do I need to replace my existing balance if I currently don’t weigh according to USP 41, but now need to "weigh accurately"?
Yes, only if the smallest sample weight is not within the operating range, which needs to be determined according to the new Chapter 41.
Can I still perform the same test using the same weights as I used to do under the old USP 41 rules?
As of December 1, 2013, the new chapter has been mandatory in the U.S.
The new guidelines have already gone into effect on December 1, 2013, and have been binding since then.
If the USP guidelines are applicable, yes; otherwise, no.