For the analytical lab/pharmaceutical users who must comply with USP, is the minimum weight to be weighed on a balance dependent on the net sample weight, or the actual weight of the vessel plus sample (gross weight)?
For example, when weighing 20 mg of standard using a weighing paper (paper = 100 mg), must the balance be calibrated down to 20 mg with a certified weight, or must the balance be calibrated to bracket the “gross” weights of 120 mg and 100mg, which are the weights that the balance actually sees.
Hi Marty,
You should calibrate balanace between minimum and maximum weight whatever you are taking. In addition we do one or two weight check between minimum and maximum weight & make a straight line to find correlation of coefficient value.
[quote=Md Tarique Nasim]Hi Marty,
You should calibrate balanace between minimum and maximum weight whatever you are taking. In addition we do one or two weight check between minimum and maximum weight & make a straight line to find correlation of coefficient value.
Tarique[/quote]
Dear all
A balance should be calibrated using a weight with a class tolerance factor greater than the readability of the balance. Example: A milligram balance with readability of 0.001g may be calibrated with a weight having a known tolerance of at least 0.0009g. There are certain Classes of Calibration Weights to calibrate a range of balances.
ANSI/ASTM Class 1 can be used as reference standard in calibrating other weights and appropriate for calibrating high-precision analytical balances (from 0.01mg to 0.1mg).
ANSI/ASTM Class 2 Appropriate for calibrating high-precision toploading balances with readabilities ranging from 0.001g to 0.01g.
ANSI/ASTM Class 3 Appropriate for calibrating balances with moderate precision, ranging from 0.01g to 0.1g.
ANSI/ASTM Class 4 Appropriate for student use and semi-analytical weighing.
NIST Class F Used to test commercial weighing devices by state and local weights and measures officials, device installers and service technicians. Class F weights may be used to test most accuracy class III scales, all scales of class III L or IIII, and scales not marked with a class designation.
*@ Tarique
I have never read or seen to calcualte Coeffecient of correlation between the range of calibaration masses. If you could come up with a valid reference then it would be appreciated. For the Calibaration procedure and acceptance criteria the attached file may be helpful.
If you plan weighing 20 mg or so in you analitycal balance you are going to have problems, in the Mettler-Toledo web site is a document titled “How to choose your balance”; for me was very illuminating and I was horrified to learn that with these kind of balances (0.1 mg resolution) you have to weigh 60 mg if you want to be in the safe side!! :mad:
I think we have to peform uncertainity test as per USP for the minimum weight you have to measure for daily analysis. Similar for the higher weight. For these min. and max. weight will be the actual weighing range for the balance
Good day!
Is there a regulated requirements for the minimum weight?
Help, please, refer to a regulatory document.
For example, that the minimum weight is considered acceptable for scales with increments of 0.01 mg?
0.1 mg?
1mg?