HOw much % of THF is safe as mobile phase

[praveenpaliwal]

Hellow experts,

I have an polycyclic compound which is soluble in hexane and THF. I prepared a mobile phase THF : Water : : 80 :20 and prepare a solution in this condition and inject. I got peak at 5.2 minutes. When I repeated II nd injection the main peak is distorted. I did not understand what is the reason behind this. The pH of the compound is slight;y basic.

Best regards

Praveen

[HPLCaddict]

Are we talking about reversed-phase chromatography?
What's the retention factor of that peak? Absolute retention times doesn't say very much...
Column dimensions, flow-rate, injection volume, type of stationary phase?

If this IS reversed-phase than a mobile phase consisting of 80% THF is veeeeery strong - is your peak really retained?

[praveenpaliwal]

Yes this is reverse phase chromatography, but my question is that how much % THF is safe for HPLC mobile phase is that any imect on pump seal when we use THF more than 50 %.

[HPLCaddict]

Before worrying about pump seals, my first question would be if you really need THAT much THF in your mobile phase. So again: Is your compound retained under these conditions?
If you really need more than 50% THF to elute your compound, I'd switch to a different stationary phase...oh, and just because your compound is soluble in THF doesn't mean that you must use THF in your mobile phase.

[praveenpaliwal]

Yes my compound is much soluble in THF and if I use more than 50% THF in methanol I got very good peak shape.My worry is that more than 50% THF is safe for my pump seal or not, Just this.

Praveen

[HPLCaddict]

I'll try it again: What's the RETENTION FACTOR of your analyte?
My point is, you might be worrying about the wrong thing - good peak shape and long lasting pump seals doesn't help if your analyte is eluting in the solvent front!

[tom jupille]

Sidestepping the chromatography issue for a moment, the answer regarding pump seals is "it depends". Not all pump seals are made of the same material. You need to check with the instrument manufacturer/vendor to find out what they recommend.