C8 vs C18

[mtorrey]

I'm wondering whats the difference between C8 and C18 columns. Yes I know one has shorter chains but what does that do?

I am trying to develop a phosphatidylglycerol method on a UPLC/TQD and am trying out different columns. This molecule is very hydrophobic and only elutes off in almost 100% organic.

I get a so-so peak with a BEH C-18 but was wondering what a C-8 would do (before I spend $600 for one).

TIA

[Uwe Neue]

In a normal gradient, the C8 column will change the elution solvent by about 5% at the end of the gradient.

In case you are using methanol as the organic modifier, you could go to acetonitrile with your C18, and get to about the same spot.

What flow rate are you using, and what is the gradient duration?

[mtorrey]

Flow is 0.350 ml/min. A: 50 mM ammonium acetate pH5. B: 90/10 acetonitrile/acetone. Gradient is 90-100 %B /5 minutes. I started out at 35 - 100% for 10 minutes but nothing comes out until almost totally organic.

Waters has a "poster" for separation of phospholipids using a BEH C8 but all I have are the C18 and I don't want to spend the money on a C8 if it doesn't make a difference.

thx

[Uwe Neue]

Well, if my colleagues presented that it worked on a C8 column, chances are high that it did not work for them on a C18 either. We all grab a C18 first...

[Bryan Evans]

Below is a gradient elution application for estradiol & metabolites
on different stationay phases:

http://www.silvertonesciences.com/files/TI375E.pdf

Different amount of (final) % organic was required in order to
keep similar retention times:

ODS - 70%
C8 - 65%
Phenyl - 60%
(widepore) ODS - 55%