Gauge R&R in Chemical Laboratory

qusys

Trusted Information Resource
#11
Re: Gauge R&R in Chemical Lab

Any laboratory test (i.e. chemical test) should be qualified and/or validated. MSA is not different than the precision and accuracy part of Q2R1. A typical protocol for a chemical test would have multiple runs, multiple samples and multiple operators. You can also have multiple days if day to day is a source of variation.
Thanks a lot for immediate replying.
In the lab there are operative procedures for the internal services provided.
There is a manual where it is reported the scope of the lab, the equipment that personnel use, the capability of performing test, traceability of the standards (primary and secondary), the competence of the personnel that are certified and qualified to perfom the required tests.
We have a software to manage tests where there are reported the spec limits.
SOmetimes we rely on approved external lab where the internal lab is not capable to perfom some required test.
Are all this item acceptable to validate methods?
I do not know the standard you mention (Q2R1).
We are not ISO 17025, but we are trying to comply.
 
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Miner

Forum Moderator
Staff member
Admin
#12
You posted this thread in the ISO 17025 forum. Do you want it moved to the MSA forum? This may help get more relevant responses.
 

qusys

Trusted Information Resource
#13
You posted this thread in the ISO 17025 forum. Do you want it moved to the MSA forum? This may help get more relevant responses.
Yes, thank you.
Could you please move it?
Could you provide some suggestion on how eventually to proceed on MSA and G R & R in this case?
:bigwave:
 
N

NumberCruncher

#15
Hi qusys

The first problem with non-replicable GRR is finding samples that have very low within-sample variation but reasonably large between-sample variation.

Given that you are doing chemical analysis, as Miner suggested, you can probably use split samples. The great thing about chemical analysis is that, unless you are doing microanalysis on very small samples, you generally have enough sample to carry out multiple repeats. The problem with chemical analysis is that the assumption of stability with time is not always justified. Solutions have a habit of "going off". Solvent evaporates, solutes precipitate or photo-degrade, or adsorb to the bottle, or react with the air,...

"This is what you do"

You measure a sample, then keep the remainder. You do this for a reasonable number of samples. You need enough samples to cover typical process variability.

For the textbook MSA, You then select 10 of those retained samples that cover the range of concentrations that you normally work with. (You obviously have records of the concentrations when you first measured the samples)

You then do a non-replicable MSA study by getting 3 operators to measure each sample 3 times (look in the MSA manual).

You must follow your normal working practice. If you follow a particular measuring regime (for example, blank, standard, standard addition, 5 x samples sample addition, blank, standard...) then this is how you must measure your MSA samples. Remember, the idea is to check how well your normal measurement system performs compared to either the product specification, or the process output. You don't adopt a special "improved" measurement regime just for the MSA process, or use samples with an abnormally large range of concentrations just to improve the figures.

Given the problems with instrumental drift, I would suggest a stability/bias check as well. If possible get a Certified Reference Material (CRM) that is reasonably similar in composition to a typical production sample. NIST do a wide variety of these, all at a reasonable price (the problem is not the price, it's how little you get for the price!)

Measure the CRM in duplicate, on a regular basis. You know your equipment. You will have to use your knowledge to judge how frequently you need to measure the CRM. Some instrumentation may drift slowly over many hours. Some instrumentation will drift significantly within less than an hour. Keep measuring the CRM over a period of weeks and use the techniques in the MSA manual to determine bias and stability.

The NIST Engineering Statistics Handbook (see link on the left hand side of the page) has a lot to say about stability and drift. It's possibly a useful supplement to the MSA manual, depending on how good your maths is.

Be aware that, for many kinds of analysis (ICP-MS, ICP-OES to name but two) the variance of your results is not constant. Typically, the error is a percentage of the reading. For example, 1ppm +/- 0.05ppm, 10ppm +/- 0.5ppm, 100ppm +/- 5ppm. If you have a very large range in your process measurements, you may find that the standard MSA calculations give odd results. (I suppose you could also argue that if your process measurements vary over two orders of magnitude, an MSA study is the least of your problems!)

Just out of curiosity, what instrumentation are you using?

NC

(p.s. Note to self. Use fewer parentheses in future posts.)
 

qusys

Trusted Information Resource
#16
Hi qusys

The first problem with non-replicable GRR is finding samples that have very low within-sample variation but reasonably large between-sample variation.

Given that you are doing chemical analysis, as Miner suggested, you can probably use split samples. The great thing about chemical analysis is that, unless you are doing microanalysis on very small samples, you generally have enough sample to carry out multiple repeats. The problem with chemical analysis is that the assumption of stability with time is not always justified. Solutions have a habit of "going off". Solvent evaporates, solutes precipitate or photo-degrade, or adsorb to the bottle, or react with the air,...

"This is what you do"

You measure a sample, then keep the remainder. You do this for a reasonable number of samples. You need enough samples to cover typical process variability.

For the textbook MSA, You then select 10 of those retained samples that cover the range of concentrations that you normally work with. (You obviously have records of the concentrations when you first measured the samples)

You then do a non-replicable MSA study by getting 3 operators to measure each sample 3 times (look in the MSA manual).

You must follow your normal working practice. If you follow a particular measuring regime (for example, blank, standard, standard addition, 5 x samples sample addition, blank, standard...) then this is how you must measure your MSA samples. Remember, the idea is to check how well your normal measurement system performs compared to either the product specification, or the process output. You don't adopt a special "improved" measurement regime just for the MSA process, or use samples with an abnormally large range of concentrations just to improve the figures.

Given the problems with instrumental drift, I would suggest a stability/bias check as well. If possible get a Certified Reference Material (CRM) that is reasonably similar in composition to a typical production sample. NIST do a wide variety of these, all at a reasonable price (the problem is not the price, it's how little you get for the price!)

Measure the CRM in duplicate, on a regular basis. You know your equipment. You will have to use your knowledge to judge how frequently you need to measure the CRM. Some instrumentation may drift slowly over many hours. Some instrumentation will drift significantly within less than an hour. Keep measuring the CRM over a period of weeks and use the techniques in the MSA manual to determine bias and stability.

The NIST Engineering Statistics Handbook (see link on the left hand side of the page) has a lot to say about stability and drift. It's possibly a useful supplement to the MSA manual, depending on how good your maths is.

Be aware that, for many kinds of analysis (ICP-MS, ICP-OES to name but two) the variance of your results is not constant. Typically, the error is a percentage of the reading. For example, 1ppm +/- 0.05ppm, 10ppm +/- 0.5ppm, 100ppm +/- 5ppm. If you have a very large range in your process measurements, you may find that the standard MSA calculations give odd results. (I suppose you could also argue that if your process measurements vary over two orders of magnitude, an MSA study is the least of your problems!)

Just out of curiosity, what instrumentation are you using?

NC

(p.s. Note to self. Use fewer parentheses in future posts.)
Hi, thanks for response.
We analyse matallic contamination, purity of DI Water, particles contamination by sampling, analysis of toxicity etc.. to support production and facilities in electronic device environment.
The lab has scales , for instance and other tool. This tool are calibrated by metrology technicians.
Then the lab has the classical tool for a chemical lab, like chromatography, etc..
The lab has also a software that is used to validate the method of the lab where there are no more than 9-10 techs and engineers.
Up to now no MSA and Gauge R & R as per AIAG blue book because these controls and the related equipment used are not in the control plan. Is this sufficient or not or MSA studies should be introduced for chemical analysis tests?
:bigwave:
 

Statistical Steven

Statistician
Staff member
Super Moderator
#17
Hi qusys

Given that you are doing chemical analysis, as Miner suggested, you can probably use split samples. The great thing about chemical analysis is that, unless you are doing microanalysis on very small samples, you generally have enough sample to carry out multiple repeats. The problem with chemical analysis is that the assumption of stability with time is not always justified. Solutions have a habit of "going off". Solvent evaporates, solutes precipitate or photo-degrade, or adsorb to the bottle, or react with the air,...
I must disagree here. The assumption of within sample variability of ZERO is not only plausible, it is required. If a sample is unstable over time, then you MUST incorporate time into your study. Assuming I was doing only a single determination of a sample. If the solution can "go-off" then it will be captured in the repeatability of the method. If the repeatability of the method is not random (degradation over time), then how do you really know the true value of the sample? You do not have a measurement system unless the sample you are measuring is stable enough to be measured. Just my opinion and my :2cents:
 
N

NumberCruncher

#18
I must disagree here. The assumption of within sample variability of ZERO is not only plausible, it is required. If a sample is unstable over time, then you MUST incorporate time into your study. Assuming I was doing only a single determination of a sample. If the solution can "go-off" then it will be captured in the repeatability of the method. If the repeatability of the method is not random (degradation over time), then how do you really know the true value of the sample? You do not have a measurement system unless the sample you are measuring is stable enough to be measured. Just my opinion and my :2cents:

Hi Statistical Steven

It all depends on where you are looking.

For day to day process measurement, I agree completely. The assumption of sample stability is required. If the sample is not stable between the time you sample it and the time you measure it, you do not have a measurement system.

However, the post to which you are referring is about carrying out an MSA study and my mindset is about dealing with the messy real world. My assumption, based upon the posts by qusys, is that the samples used in an MSA study will be process samples, raw materials ect. These are the things that s/he mentions.

In order to collect enough samples to represent process variation, you will need to collect a reasonable number over a period of time. I don't know what period of time this will be. Perhaps a few hours, perhaps a few weeks.

If the time delay between collecting your first sample and your last sample is trivial compared to the stability of the sample, there is no problem. Let's say it takes a couple of weeks to collect the samples, but the solutions are stable enough over a period of 6-9 months. No problem

If, on the other hand, it takes a couple of weeks to collect the samples but the solutions are only stable over a few days, you have an extra factor to take into account if you want to do an MSA study, namely that the concentration that you measured 2 weeks ago for solution #1 will not be the same concentration that you measure 2 weeks later.

In addition, it can be problematic simply getting the time to do the study. Analyst #1 measures the samples 2 weeks after they have been collected. Analyst #2 measures the samples a month later, he had annual leave you see. Analyst #3 can't carry out all of the measurements on the same day due to meetings, a process crisis and a general lack of interest.

This is the context in which I made the comment about the stability of the samples. It's a warning of something to be aware of.

If your calibration is carried out properly, then the long term drift of the instrument will be taken care of. Measuring CRMs regularly should confirm this. Again there are the assumptions about what and how this will be done. My unstated assumption is that the stability study will cover a period of time which will include the MSA study.

"So why are my MSA results so bad?" says Analyst. "The variance is huge and the % GRR is terrible."

"Ahh" says Know It All, "If you look at your stability study, you will see that your CRM results are statistically stable. But if you look at your process sample results in time order, you see that they change over a period of weeks."

"But they're the same samples! If they change, how do we know what the process is doing?" retorts Analyst.

Know It All strokes his goatee beard in a familiar, slightly condescending way. "Well..." he pauses for dramatic effect, "did you know that the assumption of stability with time is not always justified..." :D

Your comment is totally correct in the context of day to day measurement of process samples. But that's not what was in my mind when I replied to the post.

As I said earlier, there's no way that you can read the assumptions in my mind, I have to state them explicitly. I hope the above explanation helps.

(And not a single bracket in the whole post!!)

Oops.


NC
 
N

NumberCruncher

#19
Hi qusys

I think the issue is that you are looking for a hard answer to a soft question.

I think you are looking for a definitive "yes because..." or "no because..."

As I stated in a previous post, my reading of 16949 is that if the lab is not in the control plan there is no requirement to carry out MSA. If anyone out there disagrees, please let me know, along with why.

As I understand your question, you are effectively asking if there is there a technical need to carry out MSA?

Personally, I would say that several areas covered by the MSA manual are already good analytical practice. Checking for linearity, bias and stability are part of method validation. If you have validated your analytical methods, you have already carried out some very important parts of MSA. I think Statistical Steven raised the same basic point in an earlier post, which I can't see from the page I'm typing into at the moment.

As for carrying out the GRR part of the study, I'm afraid I can't make that decision for you. It's your process, you and your fellow employees are the only ones who are qualified to judge the risks of doing/not doing GRR.

In the process that I am involved with, a full GRR study on the analytical side is definitely going to happen. That's because the auditor demanded it. I also think it will raise issues about how good the system is and hopefully result in a better system. But that's my decision about my process.

My interpretation if 16949 in this case is that it's up to you. Maybe your auditor will disagree on his/her next visit.

NC

p.s. No brackets!!:D

Now all I need to do is stop using those damned smilies and get rid of a few ellipses...
 

qusys

Trusted Information Resource
#20
Hi qusys

I think the issue is that you are looking for a hard answer to a soft question.

I think you are looking for a definitive "yes because..." or "no because..."

As I stated in a previous post, my reading of 16949 is that if the lab is not in the control plan there is no requirement to carry out MSA. If anyone out there disagrees, please let me know, along with why.

As I understand your question, you are effectively asking if there is there a technical need to carry out MSA?

Personally, I would say that several areas covered by the MSA manual are already good analytical practice. Checking for linearity, bias and stability are part of method validation. If you have validated your analytical methods, you have already carried out some very important parts of MSA. I think Statistical Steven raised the same basic point in an earlier post, which I can't see from the page I'm typing into at the moment.

As for carrying out the GRR part of the study, I'm afraid I can't make that decision for you. It's your process, you and your fellow employees are the only ones who are qualified to judge the risks of doing/not doing GRR.

In the process that I am involved with, a full GRR study on the analytical side is definitely going to happen. That's because the auditor demanded it. I also think it will raise issues about how good the system is and hopefully result in a better system. But that's my decision about my process.

My interpretation if 16949 in this case is that it's up to you. Maybe your auditor will disagree on his/her next visit.

NC

p.s. No brackets!!:D

Now all I need to do is stop using those damned smilies and get rid of a few ellipses...
Thanks a lot.
My question was aimed to have interpretation and best practices sharing with all of you expert Covers about this topic.
I think that it is the value added of this forum to have support and ideas for the operative questions on quality topics.
To come back to the post, I would tend to go to your proposal.
It is also helpful the contribution of Steven.
At the end, MSA studies should be covered by analytic method validation that chemical lab does, G R& Rs are up to the organization.
Could also be an option that the G R& Rare not applicable because the test are destructive in their nature?
:bigwave:
 
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