Why my quantification standard is unstable?

Discussions about HPLC, CE, TLC, SFC, and other "liquid phase" separation techniques.

7 posts Page 1 of 1
Hi to all,
First of all thank you for receiving me on this quite interesting forum. I think this forum will be my benchmark for my work.
I'm writing you because I'm experiencing some issues with my quantification standard I currently use to evaluate peaks eluted at hplc and analysed in ESI MS positive ion mode.

In particular, I observe a time-dependent decrease in the reserpine-peak area (my standard) and an increase in the areas of two peaks before and after the elution of the standard. The m/z of reserpine is 609.28. the m/z under that "satellite" peaks is 639.29. There is a delta of 30.01 Da corresponding, maybe, to a CH2O.

Furthermore, I observe this reserpine modification randomly, and i'd like to identify the root of this problem in order to avoid it in the next analysis.

I don't think that the problem is instrumental, but I am strongly considering that there is something that trigger some kind of reaction in my vial. Another information is that I use a mix of reserpine and another standard ( one of the various types of organic): interestingly, irganox remains stable, whilst reserpine undergoes this hellish modification.

Does anyone experienced similar issues? How did you get rid of it? Do you have any clues?

Thank you very much
To me it seems, like you suggest, that your analyte is not stable in your vial. Which is odd because reserpine is widely used for ESI-MS calibration.

I don't work with reserpine myself. What time period are we talking about? What are the main contents of the vial? Is it acidic / alkaline ?
the mix standard is prepared in a acetonitrile and water 50/50, it is stored @ 4°C and poured as it is in a screw capped vial suitable for hplc analysis. the analysis are carried on @ 15°C. we are talking about a period of roughly 12h. I perform the analysis on 2 different intruments and i observe, randomly this modification on both the ESI-MSs.
What is the other standard in the mixture with reserpine?
Does fresh reserpine show the +30 amu peak when analyzed alone?
the other standard in the mixture is IRGANOX1098, but it does not undergo any modifications, infact its elution area remains quite stable on time.
reserpine alone does not show any 30Da shift. this modification appears during the sequent run. and this is absolutely random!! I mean that the same mix solution in an experiment is ok, but it happens that in another degradates.
If an injection shows the two peaks with the +30 amu shift, do ALL following injections from the same vial show the same effect?
I wonder if some vials, but not all, have a contaminant which affects the analysis.

I have tested three different batches of the screw capped vials I usually use for my analysis. surprisingly, after havind analysed the results, there is no batch dependent trend in reserpine area decrease, but only time dependent one. moreover, i have seen this problem also on another instrument, so I have also excluded a possible contamination of the injection needle.
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