Chromatography Forum

Hi!

I'm new to HPLC. We recently purchased an Agilent 1200 for chiral products separation (we're an organic lab, so I don't know a lot about HPLC's) and 4 different chiral columns (AD-H, AS-H, OD-H, OJ-H). Everything seemed fine.

But within less than 10 injections per column, we started having high pressure. We are in normal phase, using IPA in Hexanes. We have a column selector.

I checked the tubing and valves of the HPLC, everything is normal. The weirdest thing is that the guard columns for each chiral column are ok, the pressure build-up seems to be coming from the columns themselves! They are new! Any suggestion?

Maybe your product precipitate in your phase and collapse the head column.

I will try to mix your product in the Mobile phase to verify the solubility.

Hey!

Thanks for the suggestion. Unfortunately, I dissolve and filter all my compounds with my mobile phase before injection. So that shouldn't be the problem.

All four of the columns mentioned are silica particles coated with different chiral polymers. Any solvent that starts to dissolve this polymer can damage the column and show an increase in pressure. Take a look at the column info sheet to make sure the ratio of IPA/Hexanes you are using is compatible. I don't remember the acceptable ranges off the top of my head, but I know there are certain limitations.

I don't think the mobile phase is the problem: if i remember well, those columns can stand both 100% IPA and 100% hexane.

unless you purchased by mistake the reversed phase version of those columns (oj-rh, ad-rh etc.), and in that case yes, you're destroying the stationary phase.

more question: how much does the pressure rise for a specific flow rate?

lupetto: You are correct, these columns are compatible with the complete range of IPA/Hexane. The limitations I was thinking of are with MeOH + EtOH in the 15%-60% range. Which is clearly not an issue here.

Questions for Isa:

1-You mentioned that your guard column is OK, it's the analytical column giving the pressure increase. What guard column are you using?

2-You mentioned your sample is made up in mobile phase. What is the nature of your sample? Is it isolated material? Any chance it contains significant amounts of residual solvents used during your synthesis?

Hi!

To answer all your questions:

1) for example, the OD-H goes to 90 Bar with a flow of 0.05mL/min of 1% IPA in Hexanes. The AD-H is going over 100 (I put a max pressure of 99 Bar).

2) The guard columns are made of the same filling as the chiral columns. They are specific to the column they are attached with.

3) As for our samples, unfortunately I cannot know about every single thing people put on the columns, but they are suppused to be isolated samples, worst case crude of reaction (dry). Doesn't mean there couldn't have been some residual solvent as mentionned by Dsduncan.

oh and I checked and we bought the right column type. :) but thanks for mentionning, I didn't know those existed.

Thanks for your help! Any idea if the columns can be saved?

hello isa,
I guess the flow you used was 0.5 ml/min, and not 0.05 ml/min. correct?
just as a reference, i found old measurements i did with an OD-H (4.6 mm, 15cm, 5mu). with mobile phase heptane/ipa =8/2 0.7ml/min i had pressure of around 50 bar (without guard cartdrige). i wouldn't know the exact pressure you should expect for the mobile phase (hexane/ipa= 99/1) but it should be lower than that (viscosity of hexane is a bit lower than heptane and more importantly you have less IPA and lower flow) even with the guard column.

to conclude: your pressure is sure to high (as you know already ) , but unfortunately i don't really know why you have this problem.

as dsduncan mentioned some residual solvent in the sample could damage the column, but due to the low volume injected you probably would notice a worsening in the column performances only in the long term.

anyhow if you have more info to solve the riddle, please let us know