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   hellaround (反对自由恋爱，提倡包办婚姻) 于  (Tue Jul  8 02:45:16 2008)  提到:

I am in a very puzzling situation with HPLC-MS  andwonder if anyone had similar experience before.

I used gradient RP-HPLC to elute a standard compound (dissolved in MeOH) but got three nicely separated peaks in UV chromatogram and TIC-MS. According to the mass spectrum, the first two peaks look like fragments of the standard compound and the last peak seems the standard itself.  I had a hypothesis that the compound was decomposed before getting to MS, i.e. on the column.

The standard used is 1,2,4-acetoxybenzene, which is supposed to be fairly stable against degradation.

Does anyone have a clue what was happening?
Thanks in advance.



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   c2h2c2h2 (飞飞飞扬) 于  (Tue Jul  8 03:19:08 2008)  提到:

i don't think 1,2,4-acetoxybenzene really stable
it should be easily alcoholysized stepwise and lose one,2 or three acetyl groups
thus, the first two peaks are presumabl the decomposited products

【 在 hellaround (反对自由恋爱，提倡包办婚姻) 的大作中提到: 】
: I am in a very puzzling situation with HPLC-MS  andwonder if anyone had similar experience before.
: I used gradient RP-HPLC to elute a standard compound (dissolved in MeOH) but got three nicely separated peaks in UV chromatogram and TIC-MS. According to the mass spectrum, the first two peaks look like fragments of the standard compound and the last
: The standard used is 1,2,4-acetoxybenzene, which is supposed to be fairly stable against degradation.
: ...................



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   hellaround (反对自由恋爱，提倡包办婚姻) 于  (Tue Jul  8 04:17:49 2008)  提到:

but is it normal that the decomposition occurs on the column under chromatography conditions where there's only solvent (MeOH/H2O) flowing through

thanks a lot


【 在 c2h2c2h2 (飞飞飞扬) 的大作中提到: 】
: i don't think 1,2,4-acetoxybenzene really stable
: it should be easily alcoholysized stepwise and lose one,2 or three acetyl groups
: thus, the first two peaks are presumabl the decomposited products



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   c2h2c2h2 (飞飞飞扬) 于  (Tue Jul  8 04:25:49 2008)  提到:

i think it is possible because phenolic acetate is not as stable as alcoholic acetate.
the column may also accelerate the decomposition


【 在 hellaround (反对自由恋爱，提倡包办婚姻) 的大作中提到: 】
: but is it normal that the decomposition occurs on the column under chromatography conditions where there's only solvent (MeOH/H2O) flowing through
: thanks a lot




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   hellaround (反对自由恋爱，提倡包办婚姻) 于  (Tue Jul  8 08:54:11 2008)  提到:

thanks.

May I ask if this can be avoided, and how ?

【 在 c2h2c2h2 (飞飞飞扬) 的大作中提到: 】
: i think it is possible because phenolic acetate is not as stable as alcoholic acetate.
: the column may also accelerate the decomposition