Chromatography Forum

Recently I use NH2 column to analyze my sample and found there are much more difference with solvent peaks in reproducibility test. I use TBAH to react with the sample to form a new diol compound (I only have the diol compound reference material), then evaporate and re-dissolve in hexane/ethanol. Some times the solvent peak is too big so that it affect the quantification. Some times the solvent peak is small. Is it possible that TBAH will affect the solvent peak? If it is, could anybody help me in how can I remove TBAH from my test solution? (now I use rotate evaporate)
thank you.
PS.mobile phase is hexane:ethanol=93:7 with several drops of TBAH

How long does your column last? TBAH is a strong base, even in non aqueous environment. Don't you slowly convert your column to a bare silica one? Does the solvent peak follows a logic, e.g becomes bigger with time, number of injections or is it random?


Do you know the solubility of your diol in water? If it's not too soluble maybe you can extract TBAH with water.

Or adding a SPE step to your sample preparation (using an ion exchange cartridge to trap TBAH)?

Good luck.
bhuvfe

How long does your column last? TBAH is a strong base, even in non aqueous environment. Don't you slowly convert your column to a bare silica one? Does the solvent peak follows a logic, e.g becomes bigger with time, number of injections or is it random?


Do you know the solubility of your diol in water? If it's not too soluble maybe you can extract TBAH with water.

Or adding a SPE step to your sample preparation (using an ion exchange cartridge to trap TBAH)?

Good luck.
bhuvfe

Thank you!
The solvent peak dose not follow a logic change, but when I inject the reference standard (diol sample dissolved in hexane/ethanol without TBAH) I find the solvent peak will become bigger as the increase of concentration. But even in the highest concentration point the solvent peak will not affect the object peak.
What do you mean of 'a bare silica one'? How should I convert the column? Appreciate if you can give some advice.

What do you mean of 'a bare silica one'? How should I convert the column? Appreciate if you can give some advice.

I meant that if the column you are using is silica based (zorbax-NH2 or similar) you might have a short lifetime for such a column.

It may help if you can post the chromatogram of the standard and one of the problem sample, see link below to know how to. (viewtopic.php?f=1&t=2617)

I have a feeling that the problem is the quantity of injected TBAH (and the water that it contains since, as far as I recall, it is always a water or methanol solution with a TBAH concentration above 20%).
Maybe you can try to reduce the injected volume or to reduce the quantity of TBAH used for your derivatization/reaction and see if it gets better.

If I were you I would also try a quick drying step with MgSO4 as last step before injection.


Are you using ELSD or CAD for detection?

Thank you!
We've found out the reason with inject TBAH directly into column and find the TBAH comes out very early. In fact our object peak is affected by the substrates from our sample due to differential sample preparation, and now we try to control the whole process to make the same.
Thank you for the help.