Chromatography Forum

Hello,
We filtered some samples using 0.45um nylon filters, 30:70 (H20:ACN).
We noticed an increase in the weights seen.
A service engineer suggested it was because we used the nylon filters with the ACN.

Is this the only reason why? Also is teflon the best filter to use when using ACN?

Thanks

What do you mean by "increase in weight"? Which weight? Did you evaporate the samples afterwards? Or do you mean the result of a following chromatographic assay determination?
Nylon itself should be compatible even with pure ACN. To be sure, there should be compatibility data available from the manufacturer or supplier of the filter. PTFE is supposed to be compatible with ACN as are other membranes. PVDF or simple regenerated cellulose (RC) come to my mind first.

A simple google search reveals e.g.: http://www.discoverysciences.com/product.aspx?id=1404

A filter compatibility check (decrease in peak area or extra peaks in filtered samples?) should be a part of the method development or the method validation at the latest.

Thanks so much for your reply.

Being a non-chemist I am unfamiliar with the jargon. This would also explain why I am asking persons to verify whether this is the explanation for what I saw indeed; especially since a service engineer said it may be a reason.

I searched for filters and compatibility and came up empty.

Well lets say I was expecting 156 I got 165 instead. No extra peaks were seen, maybe the range was too restricted to see any differences.The only differences with the samples that were used is that one was filtered and the other was not.

This is the method development stage actually. Not that I know too much about LC MS method development or validation...But that is another issue.

The site indicates the filter is compatible. Just checked the results again. Will try again, but I am thinking it was a system problem. Or even sample prep.

Thanks so much once again.

One possibility that comes to mind is evaporation of some solvent during vacuum filtration.

Hi Tom. We did not do any evaporation. But maybe the sample prep was poor.

Lusi,

Are you talking ppm? Those numbers do not look bad at all; the high number is only 5.8% high which is well within requirements for most methods. If you were 5.8% high on an assay that would be a different story.

Ron J.

Lusi,

Are you talking ppm? Those numbers do not look bad at all; the high number is only 5.8% high which is well within requirements for most methods. If you were 5.8% high on an assay that would be a different story.

Ron J.

Hi, i think she is talking about the m/z in the mass spec.

Lusi,

Are you talking ppm? Those numbers do not look bad at all; the high number is only 5.8% high which is well within requirements for most methods. If you were 5.8% high on an assay that would be a different story.

Ron J.

Hi, i think she is talking about the m/z in the mass spec.

That is certainly an intriguing possibility ! Of course 156 and 165 are just numbers - without units they are meaningless.

Peter

Sorry I hadn't realise that an increase in weights can also be looked at as concentration values. As I mentioned before I am NOT a chemist, but sadly I am forced to get the work done.

Yes I was talking about the m/z values.

Sorry about the confusion.

what m/z were you expecting, did you see it before filtration, and after filtration what mass did you see?
If the mass changes, you have a different chemical present. Unless you are working on something very unstable or reactive, this shouldn't happen. Many filters will release trace contaminants into the filtrate if you're unlucky - and these could you your new ions. Was the new ion very abundant compared to the old (i.e. is it that you didn't lose your old ion, but it's now so minor you can't see it?)

The mass expected was 156, I saw 165 which by the way is possible if the method is not optimised for that compound. We were working with 5ppm concentrations and injection volumes of 1ul-3ul.

Maybe also the LC system was not optimised for the samples - maybe the column, maybe some interference or interactions with the samples that were ran before.

Since it was the first time the samples were prepared and the first time the individual did samples like these I can not vouch for the techniques. Also there could have been some contamination.

However, we will run some experiments to see whether it is indeed the filters. Due to a number of other issues we did not further investigate the problem.

All I really wanted to know if the engineer's suggestion is possible.

I would rank it as "possible but not probable".

Thanks Tom.

Will keep you all posted when we determine what actually caused the discrepancy.

If these ions are doubly charged, the mass difference is 18 Da. So this could be due to addition of water.

Tomtotom...thanks for your input...I will check it out...