Pipettes - Using ISO 8655 standard tolerances instead of manufacturer's tolerance

S

stenna10

#21
Hi,
Pipetting syringes combine the functions of volumetric (bulb) pipettes, graduated pipettes, and burettes into one hand-held device, being calibrated to ISO volumetric A grade standards. Graduated pipettes have +/- tolerances that range from 0.6% to 0.4% of the nominal volume when measured at 20C.Graduated pipettes are manufactured according to ISO specifications for accuracy and the arrangement of the graduations. A grade pipettes are more accurate than B grade pipettes and Volumetric pipettes are the most accurate of all.
 
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S

stenna10

#22
Re: Using ISO standard tolerances instead of MFG. tolerance

Hi,
Great thread. It's really better to use ISO instead mfg. Many sieve manufacturers provide a certificate which states that the sieve was manufactured in conformance with a specific standard (e.g., ASTM, ISO). This Manufacturing Conformance Certificate does not reference nor does it certify conformance of the mesh. Most manufacturers supplying a Conformance Certificate will analyze the mesh and provide a mesh certification for an extra charge.
 
Z

zamclachia

#23
My understanding of 17025 is the the testing or calibration facility have to prove that they have control over their technology. As such, all tolerances are set by the facility unless otherwise controlled by external rules (as a good example one can look at net mass control. Different economic blocks set different rules for tolerance etc.) . If this is the case, this legislation must be available.
Without been able to provide objective evidence of what the rules are, I am of the opinion that the auditor is does not understand the standard and its application.
We use an in-house spread sheet to verify pipettes. These checks are done once a month on all adjustable pipettes at nominal volume, 50% and 10% volume. The acceptance criteria we have chosen are based on the ISO standard or the manufactures depending on which has the widest tolerance. In general, as stated already, the ISO standard is more lenient.
 
S

stenna10

#24
Hi,
This is a very vital point to discuss on. The manufacturers tolerances are a way different from the ISO's. I still can't make my mind what should we follow to.
 

BradM

Staff member
Admin
#25
Hi,
This is a very vital point to discuss on. The manufacturers tolerances are a way different from the ISO's. I still can't make my mind what should we follow to.
Stenna, it's really up to you which one you choose to use. I can tell you that using the mfg. tolerances, you are going to have a lot more calibration failures.:)

I would look at what you are using them for, and the requirements. Then, decide on what tolerances you should utilize.
 
E

elenhardt

#26
Love this discussion. We're frequently asked to calibrate pipettes to manufacturer's specs by clients who like the idea of it... but perhaps don't really need it. As mentioned a few times here, manufacturer's tolerances frequently result in a great deal more as-found failures... which means as-found failure investigations, which means money and time spent. You'd want to be sure that it wasn't unnecessarily.

We always advise clients, as has been advised here, to determine what tolerances are required given the type of work you are doing. Can you tolerate 3% accuracy and/or precision? Or do you need 1% or less? (Further, what is the volume range of the instrument that you're working with? What's reasonable given the volume range?)

ISO 8655 is interesting for a number of reasons. Someone else already pointed out that the manufacturers like to tout the best inaccuracy and imprecision because it gives them a competitive advantage when selling their instruments. But let's take a look at it. (Quoting from my company's presentation on pipetting technique)

[FONT=&quot]ISO 8655 stipulates that pipettes must be adjusted to deliver correctly at 101 [/FONT][FONT=&quot]kPa[/FONT][FONT=&quot] barometric pressure (sea level), 50% relative humidity, and [/FONT][FONT=&quot]20°C[/FONT]
[FONT=&quot]Furthermore, the related part six of this standard (ISO 8655-6) requires that equipment (pipette and tips) be brought into thermal equilibrium with the sample solutions by waiting at least two hours prior to performing calibration testing.

[/FONT]
These tightly specified environmental conditions can be met in carefully designed and controlled calibration laboratories. Each manufacturer must build and maintain a laboratory at sea level that will meet these environmental conditions, and all conformity testing must occur in these laboratories.

Why? Because temperature, humidity and barometric pressure all have an effect on volume.

By ensuring that each manufacturer is testing its instruments in identical environments, we are allowed to compare “apples to apples” when shopping for pipettes for our laboratories.

Manufacturers publish and market the accuracy and precision of the pipettes they sell and use that information to position themselves favorably in the market. In other words, manufacturers compete with each other to produce the most accurate and most precise instruments.

ISO 8655 requirements ensure that performance claims are based upon instrument performance in identical environments.
Because the vast majority of scientists use pipettes in laboratories with environmental conditions that are less tightly controlled than the environment in which manufacturers test their pipettes, pipettes may behave less reliably or differently in your lab than their published capabilities.

As someone else pointed out, not even manufacturers will use the 8655 tolerances when calibrating pipettes after the sale... they are so hard to meet, especially outside of the tightly controlled environment described above.

So the question remains, what are you using your pipettes for?

I would post a link to a white paper here on the topic of tolerances that might further this discussion, but need two more posts before I am allowed. Maybe later.
 
Last edited by a moderator:

BradM

Staff member
Admin
#27
:topic:

I would post a link to a white paper here on the topic of tolerances that might further this discussion, but need two more posts before I am allowed. Maybe later.
Any time you have a link to pertinent material on any post, feel free to let any moderator know and we'll help.

Too... keep in mind copyright and stuff. So if it's a really good document but we don't have permission, we may not be able to post it. :)

But always let us know and we'll assist. :agree1:
 
D

dv8shane

#28
Update: I would appear that the auditor for the Accreditation Body is highly insistent that the work is to be done to mfg. specifications, and essentially, not recognizing the ISO specification.

I have let my vendor know I am not happy with it,:mad: as it will create huge work on our end, with no value/process improvement that I can see.

As always, your thoughts/ comments are welcome.:)
I would ask your CB for a second auditor to look at this. As long as you state which specification it is you are testing to and the conformance statement is referenced to the specification he has no right to force you to do anything. You are doing what your customer requires. Not what your auditor wants to see.
 
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