Balances are used to weigh different things as raw material, dispensed material and samples. Sometimes very low quantity is weighed for analysis. An error in the weighed material can cause a big variation in analytical results.
Assay, related substances and other quantitative analytical tests require accurate weighing for better results. Near the lower and upper capacity of the balance, weighing may be inaccurate. Therefore, a weighing range must be defined for all balances.
Related: Calibration of Analytical Balance
If any balance has the operating range from 0.01 mg to 110 gm then it should be used for weighing the material from 0.01X50 = 0.50 mg to 110X80% = 88.00 gm. Detailed guidance on the balances can be learned through OIMLR76-1 Non-automatic Weighing Instruments.
Update: Simply you can calculate the minimum limit by multiplying least count by 1000.
Minimum Weighing Limit = Least Count x 1000
- Balance for analytical use must be closed; an open balance may cause inaccurate weighing.
- Hygroscopic material gains weight when it comes in contact with the air causing unstable weighing.
- Airflow or current in the balance room may cause a disturbance in accurate weighing.
- Unleveled surface or balance may lead to inaccurate weighing.
- A vibrating surface can also cause inaccurate weighing.
Assay, related substances and other quantitative analytical tests require accurate weighing for better results. Near the lower and upper capacity of the balance, weighing may be inaccurate. Therefore, a weighing range must be defined for all balances.Related: Calibration of Analytical Balance
Weighing Range of Balances:
Some manufacturers direct in their operating manual to weigh minimum 1.0 mg on balance having 0.01 mg least count i.e. least count X 100. But the thumb rule followed in pharmaceutical industries for lower limit is least count X 50 and the upper limit is 80% of the capacity of the balance.If any balance has the operating range from 0.01 mg to 110 gm then it should be used for weighing the material from 0.01X50 = 0.50 mg to 110X80% = 88.00 gm. Detailed guidance on the balances can be learned through OIMLR76-1 Non-automatic Weighing Instruments.
Update: Simply you can calculate the minimum limit by multiplying least count by 1000.
Minimum Weighing Limit = Least Count x 1000
thank you so much it is help full.
ReplyDeleteplease give us the ISO and Auditing documents of electrical dept also sir...
ReplyDeleteinformative article
ReplyDeleteIts help full
ReplyDeleteSir
ReplyDeleteCan you please explain, which guideline is saying to fix the 80% weight as higher capacity of the actual capacity of the weighing balances.
Sir, Is that necessary to perform daily verification after monthly calibration of analytical balance????????
ReplyDeleteSir... Is that necessary to perform daily verification after monthly calibration of analytical balance??
ReplyDeleteSIR 310GM BLANCE KA LEAST COUNT KIYA HEI SIR
ReplyDeleteWhere to find the least count for a specific weighing balance
ReplyDeleteNo need to perform daily verification because all ranges covered in monthly calibration
ReplyDelete