Analysis of sea water samples, Negative mode detection

[carol]

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

[Ary]

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

[carol]

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

[Ary]

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

[carol]

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

[Sam]

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

[carol]

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.

[james little]

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.

[james little]

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..

[Uwe Neue]

Well, what is the extraction protocol?