Analytical Balance Calibration and Verification

[htquality]

Our lab is using an analytical balance and it is calibrated annually by an external provider. The calibration covers a range starting with a 10 mg weight, and the provider will not go any lower (I believe thay don't have the weights to do so).
Before each use, the lab verifies accuracy of the balance with calibrated standard weights. They go down to 1 mg and always bracket the sample weights to be weighed.
Do you see any potential issue by weighing below the minimum weight used by the external calibration lab or if the fact that we verify our range before use covers us? Any risk with regulatory agencies (FDA, EMA, ANVISA, others)?
Thank you for your help!

 

[Ajit Basrur]

Our lab is using an analytical balance and it is calibrated annually by an external provider. The calibration covers a range starting with a 10 mg weight, and the provider will not go any lower (I believe thay don't have the weights to do so).
Before each use, the lab verifies accuracy of the balance with calibrated standard weights. They go down to 1 mg and always bracket the sample weights to be weighed.
Do you see any potential issue by weighing below the minimum weight used by the external calibration lab or if the fact that we verify our range before use covers us? Any risk with regulatory agencies (FDA, EMA, ANVISA, others)?
Thank you for your help!

Calibration is defined as the set of operations, under specified conditions, establishing the relationship between values of quantities by a measuring instrument or measuring system, or values represented by a material measure or reference material, and the corresponding values realized by standards.

Thus the process of calibration establsihes that all the measurements within the range are "true" and hence using the lower and higjher weights in calibration validates your routine measurements.

 

[BradM]

Do you use this balance for assay weighing? Could this be a GLP balance? If so, then USP41 will come into play here.

I would be very interested to know why your provider can't verify that range. How low of weight is the balance used for?


What is the full range of the balance?

 

[somashekar]

Can you put here the complete label details of your analytical balance ?

 

[htquality]

Hello -
I believe the calibration company does not have the 1 mg capability and are not interested in expanding their range.
As for the balance, it is a Mettler-Toledo MX5 microbalance:

• Maximum Capacity5.1 g
• Readability1 µg
• Taring range5.1 g
• Repeatability0.8...0.9 µg
• Settling time (typical)< 10s
• Adjustment with internal weights proFACT, fully automatic time- and temperature-controlled adjustment
• Adjustment with external weights custom weight
• Linearizationautomatic linearization with each internal adjustment
• Sensitivity temperature drift± 1.0 ppm/°CSensitivity stability± 0.0001%

Thank you!

 

[BradM]

Hello -
I believe the calibration company does not have the 1 mg capability and are not interested in expanding their range.

As for the balance, it is a Mettler-Toledo MX5 microbalance:

• Maximum Capacity5.1 g
• Readability1 µg
• Taring range5.1 g
• Repeatability0.8...0.9 µg
• Settling time (typical)< 10s
• Adjustment with internal weights proFACT, fully automatic time- and temperature-controlled adjustment
• Adjustment with external weights custom weight
• Linearizationautomatic linearization with each internal adjustment
• Sensitivity temperature drift± 1.0 ppm/°CSensitivity stability± 0.0001%

Thank you!

Thanks for the details.

Is this balance used for GLP studies?
What is the lowest weight that you measure on the balance?

 

[htquality]

Yes, the balance is used for GLP activities. The lab would like to be able to use it down to 1 mg.

 

[Ninja]

The calibration covers a range starting with a 10 mg weight, and the provider will not go any lower (I believe thay don't have the weights to do so).

Before each use, the lab verifies accuracy of the balance with calibrated standard weights. They go down to 1 mg and always bracket the sample weights to be weighed.

Okay, what am I missing?

They have calibrated standard weights down to 1mg, but dont have weights below 10mg.

I've gotta be missing something obvious again...

 

[somashekar]

Yes, the balance is used for GLP activities. The lab would like to be able to use it down to 1 mg.

The AB has Max capacity of 5.1g. What is the Min capacity?
The load cell will be capable to work within its Min and Max capacity. Below Min it does not respond within its accuracy and above Max its an over load and the display indicates such.
Between the Min value and 5.1g its resolution can be like .01g , .001g or higher.
If this Min value is 10mg, then in no way you can use this for any weights less than 10mg.

 

[BradM]

If you are performing GLP studies, then you most likely will need to comply with USP 40.

You will need to determine the minimum weight capability of your balance by establishing precision using the ten readings, standard deviation, etc.

The balance needs to be verified across the use range, and corner load verifications should be performed also.

Now... if you are performing verifications before/after use using weights covering your entire range of use, then the specific test points the outside contractor is performing is less significant. I would venture they are primarily calibrating the internal weights on the balance.

However, I still think it shouldn't be a big problem for them to check at lower points.