CHANGES IN ISO/IEC 17025:2017 – SAMPLING UNCERTAINTY?

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Am I wrong or ISO/IEC DIS 17025:2016 proposes in clause 7.6.2 that laboratories performing sampling MUST evaluate “sampling uncertainty”? I...

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Posted by Alexis Oramas Pérez (Discussions: 1, Comments: 18)
Replied on March 14, 2017 12:00 am
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Dear Alexis, I would say NIL NOVI SUB SOLE ! It was already specified under the 2005 version even in the general paragraph 5.1.1 and considered by the accreditation process.
Your point 1 is not clear. Most of the accreditation bodies considered that the sampling labs are acting as the main operators. They have the responsibility of the whole measurement process. And they can sub-contract the analyses to an accredited lab. So the whole measurement shall be covered by the accreditation. Same rules apply to the sampling step and the analysis. The analytical lab is only in charge of his part. But the main operator shall consider all of the contributions to the global uncertainty, including those relating to the sampling.
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Posted by olivier NOISET (Discussions: 0, Comments: 9)
Replied on March 13, 2017 8:00 pm
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I agree with you that the sampling uncertainty is a poor estimation very often. Combination of TYPE B components through a bottom up approach where you have any few validation data available for your sampling device.
That estimation of the sampling uncertainty is maybe not the major concern in regard to the sample representativity. Knowing that, even in the framework of some legal controls, only one sample is required !
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Posted by olivier NOISET (Discussions: 0, Comments: 9)
Replied on March 13, 2017 8:00 pm
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Dear Olivier:

One thing is, as we all know, that sampling is a serious potential source of uncertainty in a measurement, and another is to say that evaluation of sampling uncertainty is a widespread practice, managed and required by accreditation bodies.

To say that ISO/IEC 17025:2005 already “required” sampling uncertainty to be determined, seems to me “farfetched”, to say the least.

What 5.1.1 states is “Many factors determine the correctness and reliability of the tests performed by a laboratory. These factors include contributions from: - sampling (5.7);” (among others).

One thing is that and another is to interpret this statement as a "requirement" to evaluate sampling uncertainty. On the other hand, ISO/IEC DIS 17025:2016 does indeed require in 7.6.2 to evaluate sampling uncertainty.
(Continues in next post...)
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Posted by Alexis Oramas Pérez (Discussions: 1, Comments: 18)
Replied on March 14, 2017 8:00 pm
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(…comes from previous post)
From your comment one can assume you know of many labs which are evaluating sampling uncertainty but, I must confess, I don´t know anyone who does it.

You are right about that everybody who takes accuracy seriously must be concerned and worry about the “quality” of the sampling, trying to get a sample as representative of the bulk as possible.

Another fact is that, from my experience, most accredited labs get their samples from their customers, who most frequently are not “a sampling lab” and much less an accredited one. What do you suggest the analytical lab should do in those cases? That´s what I was talking about in my item Nº 1.

Best Regards,
Alexis Oramas
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Posted by Alexis Oramas Pérez (Discussions: 1, Comments: 18)
Replied on March 14, 2017 8:00 pm
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Surly, for a measurement uncertainty to be taken seriously there must be consideration given to ALL potential sources of uncertainty, both type A and B, which will both exist in some form in any measurement. An uncertainty estimate that is devoid of one type or the other is simply incomplete, which then leads us to ask questions about the traceability of the observation.

It might be some sources are too small to have an influence on the overall uncertainty, and that's fine, but that still needs to be documented and argued even if omitting from the final budget estimate.
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Posted by Eugene Organ (Discussions: 0, Comments: 80)
Replied on March 14, 2017 8:00 pm
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Imagine two different first-party labs, in different factories, each of which carries out sampling in the respective production line of its factory and then analyses those samples, being both accredited for the two activities. Now, according to the DIS, they will have to evaluate sampling uncertainty, as well as that for the actual measurement.

Then, one of those two labs has the “clever” idea of making an arrangement with the production manager so, from now on, the production department is to do the sampling and then take the samples to the lab to be analysed. So, this lab can claim it doesn´t carry out sampling, thus it isn´t compelled to evaluate sampling uncertainty and simply continues evaluating measurement uncertainty.

Meanwhile, the other lab, which continues to carry out its sampling, is now compelled to evaluate them both. Do you get the picture? Isn´t this unfair?

“Isn´t this some kind of discrimination?”

Hope you get now my point.

Best regards,
Alexis Oramas
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Posted by Alexis Oramas Pérez (Discussions: 1, Comments: 18)
Replied on March 15, 2017 8:00 pm
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'Quality will out'...

I get the concern, but I suspect a company playing those kind of games will end up catching itself out and would be self defeating in the long term... I'd be very concerned about a production department being given those kind of powers... If I was looking for such a company to do work for me, I'd be steering well clear from the second company as it has put the foxes in charge of the chicken run!
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Posted by Eugene Organ (Discussions: 0, Comments: 80)
Replied on March 15, 2017 8:00 pm
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Dear Alexis,

I understand clearly your opinion. The sampling uncertainty is determined for years in some accreditation activities. Maybe you are confronted to another reality in your field of expertise. But I confirm that is is done by all the labs involved in air pollution controls from stationary sources, for example.

Now about the potential discrimination you mentioned, I think that almost all the labs confronted to customer sampling would state in the report smth like 'the result is only relating to the specific sample provided' and would not take any responsibility in terms of bias (representative sample or not) or associated uncertainty. The point is what is the weight of such statement in a report for the legislator or the control authorities ? Are they able to express more confidence to the other lab covering all the measurement process (and reporting results with larger uncertainties) ? We are talking here about the discrepancy between accreditation and legislation
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Posted by olivier NOISET (Discussions: 0, Comments: 9)
Replied on March 15, 2017 8:00 pm
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Sampling is a core part of the analytical testing method and simply the intermediate precision evaluation can give you the information that includes the variability among replicates that are collected and analyzed (repeatability uncertainty)
However the important part is the sample preparation in the lab prior to analysis
if the sampling is wrong everything is a blunder .
in any analytical testing it is the overall uncertainty in your final result when processed through a complete method that includes the uncertainty due to
sampling is important one cannot estimate the uncertainty only due to sampling as whoever has done the sampling the final analysis result is achieved only after processing through all the steps of the method
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Posted by Khalid Mohiuddin (Discussions: 0, Comments: 11)
Replied on March 16, 2017 8:00 pm
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Sampling uncertainty measurement is essential and mandatory if the laboratory want to be accredited in sampling. The estimation of sampling uncertainty is derived from the process used for estimating overall uncertainty. As Nordtest and Eurachem guides propose, sampling uncertainty is calculated from overall uncertainty and analytical uncertainty. A sampling AND testing laboratory needs to calculate the uncertainty for the analytical procedure alone (with CRMs, RMs etc) and then calculate the overall uncertainty using real samples and different approaches (duplicate samples, sub-sampling etc).

I think we should realize the division implied by "or" in paragraph 7.6.2 of ISO/IEC DIS 17025. It states "sampling OR testing". If a lab is performing only testing, analytical uncertainty must be estimated/calculated. If a lab is performing only sampling, they have to send the samples somewhere (to a subcontractor). The subcontractor needs to have their analytical uncertainty calculated.
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Posted by Efstratios Karyofyllidis (Discussions: 0, Comments: 12)
Replied on March 16, 2017 8:00 pm
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