I used ESI-QTof-MS to identify the adducts formed between phenolics and amino acids and i used Nigative mode. My question is: why my adducts m/z have higher mass than normal? For example, my adduct should be m/s 420.1 but 421.2 was detected.
Hi Mostafa, first of all, you're talking about mass-to-charge ratios, m/z (not "m/s", and especially not "M/S"). If you have a signal at m/z = 421 instead of 420, that means it has a higher mass, not charge. If 420 is the mass of your neutral species, the reason for that +1 difference is that you attach a proton (H+) to the molecule during ESI, and you detect the [M+H]+ ion in your mass spectrometer.
But Mostafa says he is in negative-ion mode, and usually molecules are detected as [M-H]-, and therefore in the m/z-1. Mostafa, can you confirm the polarity you are using in your experiment? What Matthias says makes sense, but only if you are in positive-ion mode
My adduct is formed between phenolics and amino acids for example adduct between rosmarinic acid and L-Cysteine should be 478 but 480 was found.
Okay, then I didn't read his question carefully, sorry about that. True, you should see the -1 peak in that case.
and you are sure that there is no chemistry there, right? Between those two molecules, I mean
Thanks so much for your interest. I want to inform you that my sample was directely injected into ESI-QToF mass spectrometer via a syringe pump and many isotopes for each adduct were appeared.
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