ethyl acetate as a normal phase eluent?

[hfredricks]

Hello,

does anyone have any experience using ethyl acetate for HPLC?

I'm thinking about replacing iso-propanol with ethyl acetate in our normal phase hplc method... I'd like to reduce the viscosity of our mobile phases to extend column usage and maybe get a slightly more polar eluent too. We currently use a gradient of 100% A to 50:50 A:B where A = (20% IPA in hexane) and B is (10% water in IPA)
the thing I'm worried about most is the high vapour pressure - its tricky pumping pure hexane because of its high vapour pressure, and I notice that ethyl acetate has a pretty high vapour pressure too - any comments?

thanks, Helen

[annaand]

Ethyl acetate is immiscible with water (solubility = 8.3 g/100 mL (20 °C)). So you will have 2 phases in mobile phase B.

[sepscientologist]

ethyl acetate is a very common normal phase modifier but it is much less polar than IPA. LogP values are ~0 for IPA and ~.8 for ethyl acetate.
If you want really polar then how about methanol? I'm not sure how miscible it is with hexane. ACN?

[hfredricks]

duh, sorry, I was going to replace both the IPA and water in eluent B...
methanol and ACN are immiscible with hexane, and I really need the non-polar hexane in there. Interesting about the difference in LogP - I was looking at the "polarity index" given in one of those solvent miscibility charts - though I'm not sure what that actually is... anyhoo, ethyl acetate is 4.4, IPA is 4 and hexane 0 (water 9, methanol 5.1) so i figured ethyl acetate might be a reasonable replacement... maybe not - guess I should go test if for myself!

thanks!

[martsims]

You'll push your UV cutoff up to about 260nm with ethyl acetate, this could be a problem with some analytes.

[achkata]

hi
You can use ethyl acetate but consider also ethanol.
Have you tried mixtures of hexane and one polar modifier?
give more details about column and sample

regards,
Achkata

[hfredricks]

UV isn't a problem, we're using LCMS!

has anyone experienced vapour pressure problems ? I know I can't pump 100% hexane with my set-up as it is, so I was just wondering if anyone has seen similar probs with ethyl acetate??

I had originally thought about ethanol, but didn't seem to find a suitable grade - we're doing LCMS and typically use LCMS grade IPA / water or GC resolv for the hexane... didn't see any 'good' ethanol, not that I looked too closely..

our method column is lichrospher diol but we're having to move to something else, we're currently evaluating some other normal phase options. Analytes are intact cell membrane lipids of all kinds, all in one sample, normal phase works really well!

[sepscientologist]

What kind of vapor pressure problem? Is the hexane too volatile? I setup an assay with almost 100% hexane and LCMS. I had to use APCI cuz
hexane isn't conductive. It worked well since there was no oxygen in there. I think any HPLC grade ethanol would be fine.

[hfredricks]

yes, the pump has some problems pumping pure hexane, I'm guessing it forms vapour bubbles on the backstroke of the piston or something. Adding IPA stops the problem. so since ethyl acetate has a similarly high vapour pressure I'm thinking it might do the same thing... I'd go test it right now but I'm in the middle of something else...
Hexane also destroys the insides of the degasser, I have to bypass the degasser & sonicate instead.

[WillyOne]

Even not this is not the main subject of your post, I would reccomend you to look at your HPLC system. I've worked lot of years with hexane in normal phase (-CN and Si) and I've never observed the problems you tell.
Perhaps you have a problem with the piston seal or check valves, even the solvent filters could be clogged.

[Antje_Traub]

We use a mixture of 60 % n-hexane and 40 % ethyl acetate on a LUNA silica column with absolutely no problems. It works well.
For long term storage of the column it is better to use only n-hexane.
regards