LC-ICP-MS changing signal intensity with same standard conc

Discussions about GC-MS, LC-MS, LC-FTIR, and other "coupled" analytical techniques.

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Hi,

I'm running two samples that include the same standard material, but one is dissolved in water and the other in methanol. I'm using LC-ICP-MS to quantify the sample (using water/MeOH mixture as the solvent, % MeOH increases gradually over time), but I get ~10x higher signal (peak area) with the standard dissolved in water than in methanol. Since I added the same amount of standard material to both samples, I was expecting to see the same intensity from both samples, and I'm trying to figure out why. On the LC part, maybe the autosampler has some issue with drawing methanol up and less sample got in? I'm not sure what could really happen on the MS part and wanted to see if anyone had some advice.
Did you consider degradation of the standard material in water compared to methanol? Or perhaps a lower solubility?

I'm not saying that's the issue, but it might be worth to exclude this possibility, for instance by checking the same solutions with another instrument / technique.
I followed your suggestion and ran both samples on a UV-Vis, and the methanol peak is still much smaller. The standard material has different solubility in water and methanol, but the concentration I'm using is low enough such that both solutions should be undersaturated. I also don't think the material I'm using is getting degraded because I'm seeing a single clean peak with the same retention time on both samples (whereas I'd expect shoulder peaks or other noises if my samples were degraded).
Can you tell us what compound this is?

Are the samples filtered before injection?

To clarify: with the limited information available, I think that the solution you're injecting does have a different concentration, and it's not an instrumental / method issue. Some compounds can stick to filter material, and it's very depending on the filter medium, the solvent and the of course the compound. Another possibility is that the compound sticks to the walls of the recipient.
4 posts Page 1 of 1

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