Injection of aqueous samples in normal phase HPLC?

[Alex Buske]

[quote="danko"]Hi Sassman,
[quote]Please explain why you think this is so[/quote]
Are you kidding me? If not, there you go: A very hydrophobic compound would clearly “prefer to stayâ€

[danko]

Hi Alex,

I don’t consider my words too strong but rather general. Bearing in mind I didn’t have the latest details (i.e. some RP testing has been carried out, the nature of the analyte and so on). I’m still convinced that the right RP configuration will do the job. RP is after all a much more convenient technique and in many cases less costly. When it comes to selectivity, I’ll have to disagree with you on the idea of the superior versatility of NP compared to RP. The latter can utilize a huge number of stationary phase chemistries and furthermore the aqueous nature of the mobile phase allows for one of the greatest selectivity tool, namely pH.
Btw, it’s funny how things change. In a previous post of yours (same thread) you strongly advised against water in NP (even injecting a small volume) while in the latest post you’re suggesting a mixture comprising water.

With a hexane/EtOAc/MeOH/Water gradient......

Best Regards

[Alex Buske]

Hi danko,

Just a comment: I argued against water injection in nonaqeous mobile phase. Right.
The hexane/EtOAc/MeOH/Water gradient is a GRADIENT replacing one solvent with the other and it is used in open column preparative chromatography. No way of re-using the silica gel for a second run.
NP can be extremly versatile and fast, especially for prep separations.
I agree: if there is a RP method it is often easier to use.
Alex

[mohan_2008]

Paroma:

Did you try a Reversed phase ion pair method, with a sulfonate ion pair. This should solve your problem. And you should get your selectivity.

[HW Mueller]

Did someone actually use ion pair reagents on prostaglandins? Lipids have been done on both NP and RP, longer on NP. Taking a look at the TLC classic by Stahl might be very instructive here.
Also, one might not call this pH control, but acidity and basicity have been neatly controled in NP by adding a bit of acetic acid or an amine. I guess that was done before many of you were born?