Filtering samples before analysis by IC

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

13 posts Page 1 of 1
Ok, so I am now having a problem with our new QA/QC officer on methods EPA300.0 and EPA300.1. He is saying that since the method says we must inject a well mixed sample, that we MUST shake the sample prior to injection and not filter it before it goes on the instrument. When we argue the point that it needs to be filtered he says that the EPA chemist are more experienced than we are and if it needed to be filtered they would have put that into the method.

Does anyone know of any official reference that I can use to show that the samples should be filtered prior to analysis?

I am afraid to show him that the autosampler has an inline filter for when it loads the samples for fear he will want to have that removed also. He is arguing that it is "good chemistry practice" to mix the sample before injecting it, but is ignoring the "good chromatography practice" of proper sample prep.

Any reference would be much appreciated, especially if it comes from a government agency link.
The past is there to guide us into the future, not to dwell in.
James_Ball wrote:
Ok, so I am now having a problem with our new QA/QC officer on methods EPA300.0 and EPA300.1. He is saying that since the method says we must inject a well mixed sample, that we MUST shake the sample prior to injection and not filter it before it goes on the instrument. When we argue the point that it needs to be filtered he says that the EPA chemist are more experienced than we are and if it needed to be filtered they would have put that into the method.

Does anyone know of any official reference that I can use to show that the samples should be filtered prior to analysis?

I am afraid to show him that the autosampler has an inline filter for when it loads the samples for fear he will want to have that removed also. He is arguing that it is "good chemistry practice" to mix the sample before injecting it, but is ignoring the "good chromatography practice" of proper sample prep.

Any reference would be much appreciated, especially if it comes from a government agency link.


EPA 300.0 at point 4.4 says that water with particles must be filtered to prevent damage to instruments!

Plus point 9.3 of this ASTM says the same thing.

http://file.yizimg.com/175706/2011120911102615.pdf

Hope this helps, unfortunately the QA/QC jobs often goes to people who have never ever ran an instrument in their life.

Davide
Davide Balbo from Italy
Hornet wrote:
James_Ball wrote:
Ok, so I am now having a problem with our new QA/QC officer on methods EPA300.0 and EPA300.1. He is saying that since the method says we must inject a well mixed sample, that we MUST shake the sample prior to injection and not filter it before it goes on the instrument. When we argue the point that it needs to be filtered he says that the EPA chemist are more experienced than we are and if it needed to be filtered they would have put that into the method.

Does anyone know of any official reference that I can use to show that the samples should be filtered prior to analysis?

I am afraid to show him that the autosampler has an inline filter for when it loads the samples for fear he will want to have that removed also. He is arguing that it is "good chemistry practice" to mix the sample before injecting it, but is ignoring the "good chromatography practice" of proper sample prep.

Any reference would be much appreciated, especially if it comes from a government agency link.


EPA 300.0 at point 4.4 says that water with particles must be filtered to prevent damage to instruments!

Plus point 9.3 of this ASTM says the same thing.

http://file.yizimg.com/175706/2011120911102615.pdf

Hope this helps, unfortunately the QA/QC jobs often goes to people who have never ever ran an instrument in their life.

Davide


Thanks for spotting that.

I asked my analyst and he said the QC guy is telling him that allowing the sample to settle or centrifuging the sample prior to filtration is not allowed because those two things are not equivalent to filtration. When a sample is full of solids it will take maybe 10 filters to obtain a clean sample in enough volume to run the analysis if the sample is shaken just prior to filtration. After pointing out section 4.4 of 300.0 I now have to convince him that centrifugation is equivalent to filtering and that settling is equivalent to very slow centrifugation.
The past is there to guide us into the future, not to dwell in.
Does he even allow you to use an autosampler if he wants it to be shaken and injected right away.... ?
He first said if it settles in the autosampler tube that would be ok. Of course we then pointed out that would cause the sampling needle to clog once all the solids settled. He then took the section 4.4 of method 300.0 and allowed us to filter the samples, but we still had to shake them before filtering.

After showing that it took over 10 filters to get enough sample filtered to fill a 10ml sample tube, he then wanted to if we could stack filters of increasing porosity to prevent clogging. We pointed out that it would still add up to the filters costing over half of what we charge for the test, and since most of our competitors already charge less than we do increasing the price is not going to happen.

Right now we have submitted the question to EPA for clarification if centrifuge and settling are equivalent to filtering or can be used in addition to filtering(it is even written into other methods that they are the same thing) so hopefully we will have it cleared up soon.
The past is there to guide us into the future, not to dwell in.
It could be an option to increase the 'needle depth' setting (increasing height from the bottom) in the autosampler software, so you can centrifuge/let it settle in the IC vial itself, without the risk of putting the needle in the solid part.

It depends a bit how easily the solid film is disturbed by the autosampler, but we do this for some methods to save time on preparation.
My goodness what agony. Your QC guy needs to understand that when an instrument is down, you are not making money. In fact, you are losing. It takes time and materials (both = money) to repair it.

What are your analytes? is there a risk of the filter medium extracting them as the sample passes through? Perhaps you could verify that it doesn't happen by some sort of standard-addition type experiment?
James_Ball wrote:
He first said if it settles in the autosampler tube that would be ok. Of course we then pointed out that would cause the sampling needle to clog once all the solids settled. He then took the section 4.4 of method 300.0 and allowed us to filter the samples, but we still had to shake them before filtering.

After showing that it took over 10 filters to get enough sample filtered to fill a 10ml sample tube, he then wanted to if we could stack filters of increasing porosity to prevent clogging. We pointed out that it would still add up to the filters costing over half of what we charge for the test, and since most of our competitors already charge less than we do increasing the price is not going to happen.

Right now we have submitted the question to EPA for clarification if centrifuge and settling are equivalent to filtering or can be used in addition to filtering(it is even written into other methods that they are the same thing) so hopefully we will have it cleared up soon.


I would analyze the same sample twice. The first is the filtered sample and the second one after centrifigue and not mixed.
If the difference between the two results is less than your repeatability limit then you know your procedure is good.
Davide Balbo from Italy
James_Ball wrote:
Ok, so I am now having a problem with our new QA/QC officer on methods EPA300.0 and EPA300.1. He is saying that since the method says we must inject a well mixed sample, that we MUST shake the sample prior to injection and not filter it before it goes on the instrument. When we argue the point that it needs to be filtered he says that the EPA chemist are more experienced than we are and if it needed to be filtered they would have put that into the method.


Well, before I was retired, I had to deal with similar, from both QA and from my pointy-haired boss (ala Dilbert comic strip). Of course the sample should be mixed. And EPA, etc. don't generally specify removing particles and undissolved stuff by a certain procedure anyway, that is just good general practice. Sure, one should investigate (like in the quote below) as to whether filtration alters the analyte level, or introduces extraneous interferences etc., but that's all understood as part of good practices. Just like EPA doesn't specify "JT Baker" or other brand of solvent, or filter or autosampler vial, doesn't mean that such should be checked out.

And QA should NOT assume that EPA guy/writer knows more about that procedure than you do, could be right, could be wrong. When I worked with USP and house-developed and house-validated methods, had to fight with QA and supervisor all the time. Stuff like how "flat" the baseline of a placebo needed to be in the elution time of the analyte; when magnified enough, anything looked like little bumps (remember: we had fragranced consumer products, and most pharmaceuticals were not fragranced).

We had hand sanitizer products with 60% or more ethanol, we still had to validate the procedure for our product because USP only had for water-ethanol solutions, and we also had to determine ethanol detection limits even though that was a zillion orders of magnitude less than our working concentrations.


Hornet wrote:
I would analyze the same sample twice. The first is the filtered sample and the second one after centrifuge and not mixed.
If the difference between the two results is less than your repeatability limit then you know your procedure is good.


I still feel that filtration (after checking for analyte loss or interferences) is a common practice and does NOT need to be validated every for every procedure. But hopefully what Hornet suggested should convince QA.

One time I had to document in a report that QA Director was present at such meeting on certain date and decided for the company that he wanted the active reported as total active, even though some of the active (an acid) esterified with the substrate (alcohol) in situ to form esters.

I was not comfortable with that, not the same as (for example) reporting salicylic acid content as the amount of sodium salicylate acidified to be salicylic acid so all could be quantified....
Hi James

If you take the method literally then you should shake and inject.

But any method that specifies that you have to have particles in your reagent water;

7.2 Reagent water: Distilled or deionized water, free of the anions of interest.
Water should contain particles no larger than 0.20 microns. (https://www.epa.gov/sites/production/fi ... 1_1993.pdf)

should probably be interpreted quite loosely.

Peter
Peter Apps
We finally got a reply directly from the EPA which more or less said that if the client was ok with it, to shake then let samples settle then filter and inject. This is what we have been doing all along. They said that is what they do in their labs.

This was just a common sense practice that wasn't spelled out in detail in the method itself. QA is ok with it now, but just as with anything else you have to have something in writing since common sense isn't admissible in court.

Of course the EPA also said if the sample is bi-phasic and the client wants both phases run ( which would be the water and the settable solids) then to separate and run the water then run the solids as a solid sample. Of course the way the method says to run a solid sample is to take the solid sample, mix it in a 1:10 ration with DI Water, filter and inject. Seems to me that is pretty much what the whole sample is anyhow if it comes in as a mixture of water with sediment in it. :roll:
The past is there to guide us into the future, not to dwell in.
I am so happy I have always been in R&D and have not had to deal with such ridiculousness!!!

Centrifuging then filtering is very common for samples with a lot of undissolved solids ...

You are only going to see analyte that is in solution no matter matter which way you do it...

If it's adsorbed on the solids, not removing the solid would not change that - only clog the instrument!

Anyone who does not understand that should not be allowed to have an opinion about how things need to be done IMO!!!

- karen
Karen01 wrote:
I am so happy I have always been in R&D and have not had to deal with such ridiculousness!!!

Centrifuging then filtering is very common for samples with a lot of undissolved solids ...

You are only going to see analyte that is in solution no matter matter which way you do it...

If it's adsorbed on the solids, not removing the solid would not change that - only clog the instrument!

Anyone who does not understand that should not be allowed to have an opinion about how things need to be done IMO!!!

- karen


I totally agree. But seems lawyers always have an opinion even when they have no knowledge of the subject. :lol:
The past is there to guide us into the future, not to dwell in.
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