Chromatography Forum

I'm trying to separate an amine impurity (pka = 9.06) by using SPE using DSC-SCX (6ml, 1gm). The conditions are as follows:
conditioning the cartridge:
3 ml of MeOH
3 ml of H2O

Then load the sample (pH=7)

Elute:

Nacl/NaOH (pH=12) , recovery is only 85-90%
Nacl/ KOH was alos tried, but the recoveries are 75-80%.

Can someone suggest me the elution coditions to have good recovery?
Thanks.

RG

Depending of what your sample is 85 - 90 % is not bad.

how fast are you loading your sample?
if your PKA=9,06 then pH should be good; could you try go lower maybe pH6; also whan you condition your SPe cartridge; only to be sure your amine is 100% protonated. As alway; try to run any elution step in yor chromatographic system; in order to understand what is wrong.

If your molecule is quite apolar, it may need some organic solvent in the eluent (usually methanol). Methanol can be incompatible with salt (precipitation) but you can keep basic pH with NH4OH instead.

Sometimes, it's necessary to have a sample pretreatment with acid or buffer to prevent protein binding which can lead to losses (for plasma matrix for example). In this case the SPE is also conditionned with the same buffer/acid instead of pure water.

Information on your matrix could also be helpfull.

Thank you guys.

The sample matrix is mono and dibaisc sodium phosphate buffer. The sample solution pH is 6-7.
The active molecule is degraded into the impurity which is very polar (2-chloroethylamine). This is the impurity that I have to selectively separate from the drug product solution and then analyze by GC-FID.
I'm using SCX cartridge. At pH=6-7, the active molecule is somehow getting retained about 70-75% due to hydrogen bonding (most likely), whereas the imp (2-CEA) is protonated and thus retained onto the cartridge. So the selective elution of the 2-CEA imp is desired.
Thank you.
Rgonsal

in my experience most people accept 85-90% as fine for an SPE process. Especially if it is consistent. Is this a manual or automated SPE process.