Is Metals Analysis of Water Samples considered "sampling"?

Bev D

Heretical Statistician
Staff member
Super Moderator
#11
Here's what my organization uses and I've been able to justify it statistically to the USDA, FDA, ISO and various other regulatory and customer auditors, including their statistical staffs.

"we test every batch (lot). we test a xx volume sample from a xxx volume sample sent from the supplier." this avoids the whole 'sample size' question that seems to be causing confusion...

statistically, you are 'sampling' from every batch. your sample 'size' is 1 sample of xx volume.
 
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Ninja

Looking for Reality
Staff member
Super Moderator
#12
The words are confusing...but there seems to be general agreement on this thread that you ARE sampling:

You are simply not into any statistical sampling.
You ARE sampling...you are not into any "statistical sampling".

sam?ple

noun 1. a small part of anything or one of a number, intended to show the quality, style, or nature of the whole; specimen.

If you aren't using it all, you're taking a sample.
If so, would a simple statement in the quality manual to the effect that our methods ensure that we test a representative portion of the samples that are sent to us?
You test a representative portion...you are sampling.

...
"we test every batch (lot). we test a xx volume sample from a xxx volume sample sent from the supplier." this avoids the whole 'sample size' question that seems to be causing confusion...

statistically, you are 'sampling' from every batch. your sample 'size' is 1 sample of xx volume.
... If you are not testing the entire lot you have received, then you are using samples of that lot.
your sample size is effectively 1.
We're all saying YES...you are sampling. Many have commented further on the details...I snipped thouse parts out, but they are good input.
I don't think there is any question that you are sampling...it is just a matter of how big, how taken, how many...

Does this clear it up?
 
J

JodiB

#13
No, I'm sorry to be so dense on this. But I am specifically referring to 5.7 Sampling in ISO /IEC 17025....5.7.1"The laboratory shall have a sampling plan and procedures for sampling when it carries out sampling of substances, materials, or products for subsequent testing or calibration. The sampling plan as well as the sampling procedure shall be available at the location....." and 5.7.2 " the laboratory shall have procedures for recording relevant data and operations relating to sampling that forms part of the testing or calibration that is undertaken. These records shall include the sampling procedure used, the identification of the sampler, environmental conditions (if relevent)....."

So I was told by someone that the customer was determining the sample points so none of this applies to us. Now, it seems that this does apply to us but I have no idea of how to write a "sampling plan" or "procedure for sampling".

Would our method (which states how much volume to use for testing) meet the requirment for "sampling plan" and/ or "procedur for sampling"?
 

Ninja

Looking for Reality
Staff member
Super Moderator
#14
Okay, let's try it this way.

You get a water sample from a customer. From customer A, you get a quart. From Customer B you get a liter, from customer C you get 500grams.

You need 4grams to do your test.

You take a sample of what was provided to you.

You need a sampling procedure something like:

"The as recieved specimen will be shaken by hand for no less than 10 seconds, then allowed to sit for no more than 2 minutes.
A 100ml glass pippette is inserted approximately to the halfway point of the specimen container and at least 10ml of sample is retrieved.

From this retrieved sample, an amount of 4 grams (+/- 0.1gram) is weighed into the test cylinder."

And on and on...

This is your sampling procedure for a certain class of liquids for which it is appropriate. For another class with heavy suspended material you may define the sampling method differently...to ensure that your sample is representative of the stuff that showed up at your door.
I bet (hope) you already have these procedures in place...you just need to write them down.

You need the sampling plan, and sampling procedure, so that some knucklehead doesn't try to sample a sedimented suspension by pulling a sample from the top supernatant liquid that is not representative of the material received, then reporting to your customer that his cadmium contaminated water is just fine. This is also why the sampling procedure "shall be available at the location"...so the proper way to take a sample is available right at the work station.

Don't be confused that the stuff showing up at your door says "sample"...

to your testing, the stuff that shows up at your door is the population. You are taking a sample from that population.
How do you do so? That's the plan and procedure it's talking about.

How was that one? Any clearer?
 
J

JodiB

#16
Short answer: yes.
Thanks Bev! This is the answer that I've been reaching for.

Ninja, thanks for the detail. We do say those things in our written methods.

I'll agree with everyone here that we are "sampling". But since I'm not familiar with what is typically used as a "sampling plan" or "sampling procedure", I didn't know if our methods would meet this requirement or if there is some other document(s) that needed to be created.

So I will amend our quality manual to say that our sampling procedures / plans are addressed in the laboratory methods, rather than saying that there are no sampling activities in the lab. Does this sound like it will pass muster?
 
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