Chromatography Forum

Hi all,

I have a rare problem using a batch of n-heptane in a Gilson 322 pump. It is a semi-prep pump. I use this equipment for chiral separations.
Which are the problem? Well, when I try to use the Batch Nº8 (example), the A channel of this pump cannot aspirate this n-Heptane.
I have changed inlet and outlet check valve. Also, piston seal, with no results.
Next, I have changed to put on channel B, and this channel has stopped to aspirate.
Well, when I had come to this part, I have tried to use a previous batch. In this case, the pump works correctly.
So, the problem is in the Batch. But I have made a dry residue test with no result. Also an 1H+NMR (in CDCl3-d), but there are not any strange peak.

We have not changed the supplier.

Has anyone had this problem before?
I have no evidence to offer to the provider.


Many thanks in advance for your help.

Hello

In my opinion it has nothing to do with heptane batch. It is more problem with pump.
When you start pumping and flowrate is to high there is a possibility that you have air in pump chamber, around plungers (small air bubbles can cause problem with pumping liquid).
So I'd recommend to flush pump (use syringe and gravity) and then switch flow to higher value.

Regards

Tomasz Kubowicz

Hello Tomasz,

Thanks for your answer.
I had purged with Isopropanol. I had also degassed.
I have mentioned that if I use a previous batch, the pump works. Just in the momment that I change a bottle from old batch to new batch, starts the problem. Then, if I change the new batch for the old one, the pump works correctly.

Do you still think that pre problem is in pump?

Thanks

Hello

So what is the difference between batches? If you have pure heptane and heptane mix with ethanol pump does not know that...so if you have pure heptane (batch one) and heptane with 0.5% of soemthing (miscible of course) pump should work the same way.

Regards

Tomasz Kubowicz

Hello,

I had also tried to use a mixture of 95%Heptane 5%Ethanol. It did not work with the problematic Heptane but worked with the old batch.

So...

Hello

So...get rid of problematic batch and use new one.

Regards

Tomasz Kubowicz

It is not unknown for the wrong label to get onto a bottle. Does the unpumpable heptane smell the same as the pumpable batch ? If not it is either not heptane at all, or it has contaminants in it that raise the vapour pressure enough to cause cavitation in the pump.

Do you have a GC ? Run some of each.

Peter

Hello,

All about this topic is to try to determine any test to prove that there is a contaminant in this n-Heptane.
After making a GC-MS, the conclusion is that there is not anything.
The only proof that there is a contaminant is my nose. After dry residue, it has left a peculiar smell.

Hope the supplier take it in consideration.

Many thanks for your answers

Assessing solvent purity can be very tricky.

From what you've told so far I'd go for a dual-channel UV/VIS spectrum in 50 mm (better 100 mm) cuvettes.

I've had a similar encounter some years back and the cause was a contamination of around 100 ppm steering gear oil. Solvents are usually shipped in tank waggons which are not always properly cleaned from their prior contents so you sometimes get very interesting effects.

As such fluids have dyes as means of identification, a UV/VIS can detect such contaminations in the low ppm range.

I found that out quickly as we're subjecting all samples to a two-channel UV/VIS scan of a known good sample vs. the new sample.

And if you actually have a smelly residue I'd recommend to concentrate like 10 ml of solvent and analyze the residue with FTIR and NMR.