Chromatography Forum

Hi all,

I've testing a method that will analyse compounds from sea water samples. I do extraction of the compounds using SPE and I analyse my extracts using MS/MS (Quattro micro, ESI). I tested the method on spiked samples but compounds that required a negative mode for their detection can not be detected . Does any one know why? Did any one have similar results? I tested the method with others types of compounds and they don't have that problem.

Thanks
Carol

Carol

Have you checked the Quattro is running ok in negative ion by running the negative ion spec (raffinose I think?). I have seen sometimes the instrument will be fine in positive but give nothing in negative, this is usually a hardware problem. Run the spec and then give the factory a call, they should be able to help you out over the phone with any other possible fixes. If you are running a switching method between negative and positive there is a minimum switch time (0.2sec ? its been a while so my memory may not be spot on). They are the first two things I'd check.

Steve

Hi Steve,

The thing is; I run a standard just before the sample and I have signal for the standard but not for the samples. I know I have compounds in the samples because I put it my self because of that I think it is a matrix problems but I also thought that maybe there is a relation with MS and sea water.

Thanks

Hi Carol

I would definitely go for running the negative ion spec. It will be in the manual. It used to take only a few minutes to run but it will put your mind at rest that the instrument is performing OK. I cant see (no pun intended) any reason the sea water should interfere in anyway as you say you have done SPE and I assume you are running some chromatography. Have you tried spiking your standard into your matrix (sorry I'm a bit confused between your first post and the last one as to what exactly you have done with your standards/spikes)

Steve

Hi Steve,

Thanks for your help. I had my samples, collected from the sea and I spiked then with all my target compounds. I did the extraction protocol and run then through the HPLC. The way I set up my run was blanks, standard at 25 ug/l (Stnadard that I prepared in the lab withoud the samples) and finally my samples which I repared as describe before.
I hope that is clear. I am going to try what you say to me and add the sandard again in to the extract to see if is the matrix.

Thanks,
Carolina

Carol:
The extraction method may have problem. Have you spiked the exctracts with your standard?
Sam

Yes,

I spiked my samples with a sandard which is a mix of all my target compounds. The extrange thing is; I tested in River, tap and sea water and I can detect all the compounds excep the compounds which need negativce mode from Sea water. I know is not the MS because before my samples I run the standard I added to the samples diluted and all the compounds are present.

I also thinhk is the extraction protocol but I was wondering is somebody had the same type of problems.

Thanks.

might try infusing your standard at low level post-column using a t and an infusion syring. While doing this, inject your sea water extract. That will tell you what part of the chromatogram gives you matrix suppression for your standards.

for post column infusion approach for matrix problems,

see

Rapid Communications in Mass Spec, 13, 1175-1185 (1999), Ryan bonfiglio et al, Merck Research Laboratories..

Well, what is the extraction protocol?