critical mass

[mondy]

Please ,can somebody help me.What is the recomended minimum mass I can measure on my analytical balance if readability is 0.1mg ,0.01mg,0.001mg. Does somebody know any guide about that.Thank you in advance.

[DR]

The USP general chapter <46> goes into this. Basically, you're "accurately weighing" if:

0.001>3(Stdev)/(mass weighed)
where Stdev is for n=10 weighings of a given standard mass.

So, using manufacturer provided "reproducibility" specs and assuming modest tares for weighing vessels:

Mettler AT261 is good down to 45mg even though it reads down to 5 places when set to read grams.

Sartorius M2P is good to 3mg though it reads 1/1000 mg.

[Bruce Hamilton]

You can go to the Sartorius site for a table of data on their current models, and an explanation of the USP equation given above by DR

http://www.balances.com/sartorius/minim ... eight.html

I couldn't find the equivalent information in a nice table on the Mettler site, but you can probably assume their models will have similar values.

You, or your calibration service, are supposed to determine the value for your balance in your environment.

Please keep having fun,

Bruce Hamilton

[mondy]

Thank you ,
it was very useful .