Chromatography Forum

I have an Agilent 5890 and I found a port that goes to the inlet of my COC injector that provides cryogenic cooling via a gas line. I believe I may be able to get more runs in per day if I had crygogenic cooling.

I want to know what everyone's experience is with cryogenic cooling, it's advantages (aside from fast cooldown of inlet) what disadvantages it has, what kind of specialty equipment is needed (if any) in addition to a N2 cylinder and a valve. Is it very costly to operate?

Thanks!

I can't comment on the liquid Nitrogen option, but the liquid CO2 option results in increased baseline noise at temperatures below 20C, and I suspect the liquid N2 would as well, as it's due to the pulsed nature of the cooling..

I found it was good to cool the instrument oven down quickly from about 70C, but the baseline noise increase was intolerable if used to control the oven for trace analysis of HCs using FID and a long fused silica capillary or PLOT column. Never tried it with a packed column, and TCD was less sensitive to noise.

I suspect it's sometimes better to go to a thicker film ( higher initial start temperature), and use the cooling just to bring the temperature before the run.

It's easy to use, and worth ensuring you have a good filter in the line because the orifice is quite small, and the coolants have habit of carrying fines into the orifice.

The trick with liquid CO2 is to ensure the main cylinder headspace is the hottest part of the system, it keeps the lines full of liquid. As cylinders are often stored elsewhere, it's worth ensuring they are warm. My solution was to pour a bucket of hot water over the cylinder every hour or two on cold days...

Please keep having fun,

Bruce Hamilton

let's say you want to cool the inlet down from 380 deg. C to 50 deg. C. just the inlet, not the detector or oven. lets say you're using liquid nitrogen. how does that impact the baseline noise, and does it stabilize over time? does it take more time to stabilize the baseline than it would to allow the inlet to cool down ambiently?

we're using an FID cool on column injection and a metal column, not TCD's or packed columns. are there any specific recommendations for those?

If you only want to go to 50C you would do better with liquid CO2 than with liquid N2. A major advantage of the CO2 is that you can keep the cylinder indefinitely, whereas N2 evaporates from the container whether you use it or not. The plumbing for CO2 is also simpler.

Peter

ece,

As an alternative, try compressed air. SimDis instruments use this to cool the inlet, you can tap into already existing lines, you don't have to go that cold, and you don't have to fuss with extra cylinders or dewars.

Best regards.

that's a really good tip! that would probably cut my inlet cooling time by 75%!

One thing you need to do before you connect anything to the port is to verify what cryogen the COC is designed to be cooled by. Liquid CO2 comes out of the cylinder at 900 psi, while liquid nitrogen is 22 psi. Hooking up liquid CO2 to a liquid nitrogen valve leads to a dangerous situation. I have actually seen an explosion in a piece of equipment caused by the wrong cryogen.

Ron, good point. I will ask Agilent whether or not I can just hook up a compressed air cylinder with a regulator.