Calibration of balances, weights, and required check range

Discussions about sample preparation: extraction, cleanup, derivatization, etc.

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Every lab I've worked in had someone come in and check/recalibrate our balances once a year. In the days of mechanical balances, I don't recall running check weights but memory may be foggy. That was back in 74 to 86.

When digital balances came along; again, the balances are checked once a year but class 1 (or better) check weights were required each day of use. Some labs required we bracket the range typically used on a particular balance and others required a high and low mass anywhere in the range.

I don't remember if we had to send the weights out for recalibration. My recall is that when the balances were checked, the technician would compare our check weights to theirs on our balance and certify them good for our use.

What are the requirements for your labs?
The Fifth Edition 'EPA Manual for the Certification of Laboratories Analyzing Drinking Water' Chapter iV section 7.1.3 (loosely quoting says): that ASTM Type 1 Class 1 or 2 weights must be recertified at least every 5 years. Also, that each day a verification should be performed with a check reference mass at approximately the same nominal mass to be determined. Further that the reference weights should be calibrated anually against the reference weights at the time of balance calibration.
Every certifying agency has their own rules it seems. We are now held to having the check weights recertified every 6 months through our NELAC group. We have to check the calibration each day "weighing is performed" so if we don't weigh anything for a few days we don't have to check it.

The reference weights that we check the check weights against I think are being recertified by sending them to NIST once a year, but I am not certain about that frequency.
The past is there to guide us into the future, not to dwell in.
You have "reference weights" for your "check weights"? Do your balances not autocalibrate? Is that why you need reference weights; to calibrate the balances? Or do you use the check weights daily and periodically check them against the reference weights? I'd like to see the broad outline of an SOP for that. It seems like they are reqiring a double backup of check weights.

I ordered a 'TROEMNER 7257-1W Analytical Precision Class 1 Cal-Pak with NVLAP Accredited Certificate, 200g, 20g, and 200mg Capacity' so I can keep operating while my other weights are sent out for certification. 200g is the largest recommended calibration weight for my analytical balance so I think that is covered as well. I'm considering also buying a 2Kg class 1 weight when I have funds.
We have a company that comes in every 6 months to service and calibrate the balances, but we are required to verify the calibration with check weights ever day. We have one set of "reference" weights we send out to be checked by NIST, and those we use to verify the "check" weights so we don't have to send them all out. We have several balances spread all over the building and we it is not easy to use just one set of weights to verify all the balances each day so we have a set at each balance.
The past is there to guide us into the future, not to dwell in.
Dear LALman

Do you also check the minimum weight in your balances? I hope so because many people are weighing 10 mg in an analytical 0,0000 g balances!

Fernando
Like James, I only check my balances and pipets if I am using them that day. I do that check with one of my two class 1 5g and 100mg sets. I've decided that once a quarter I will check the whole range with the 200g, 20g, 200mg certified class 1 set. I do not have a 10mg weight. However, when I weigh out salts for standards, I am in the gram range or higher and my smallest autopipet is 100uL.

Once a year I have someone come in and certify my 4-place analytical balance. I found out last year that they are checking with Class 2 "S" weights. On the face of it, those would seem to be less accurate than my own set. But maybe the method (HB-44) overcomes the accuracy deficiency?
Hi All

Again it is OK you are verifying accuracy, but what about precision? In my case we follow USP 41.

Best regards.

Fernando
Fernando wrote:
Hi All

Again it is OK you are verifying accuracy, but what about precision? In my case we follow USP 41.

Best regards.

Fernando

Fair point. When checking hand pipette delivery, I weigh the delivery 3-4 times for a pipette volume check. But I've never worked at a lab that did required us to weigh the check mass repeatedly.
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