Column Diameter Required for High Pressure HPLC

[hajdaei]

We have been thinking a lot about high pressure HPLC in our laboratory.

I am well aware that when you go to very high pressures you have to reduce the diameter of the column to minimize the radial temperature gradients (caused by viscous heating).

Here's my question: How high can you go while still using a standard 4.6 mm column? Can you go to 7000 psi...8000 psi....etc. And how about with a 3.2 mm ID column.

This is important because we are trying to figure out what pressures we can work at without having to take on all the difficulties of extra-column effects.

Thanks

[Kostas Petritis]

The paper below will reply your question in terms of pressure vs column ID vs flow rate.

LCGC NORTH AMERICA VOLUME 21 NUMBER 7 JULY 2003

But I think the other problem is the engineering of frits of these diameters that can withstand ultra high pressures...

[Uwe Neue]

The general story is that you will get better results for a smaller diameter, provided your system bandspreading is small enough to let you do that.

My recommendation is to look at J. R. Mazzeo, U. D. Neue, M. Kele, R. Plumb, “Advancing LC performance with smaller particles and higher pressuresâ€

[hajdaei]

Does temperature make any difference.

In other words, if we are working in an oven at, for example, 70C would we be able to use a larger ID vs the situation at room temperature (bear in mind that we are still at high pressures).

It seems like dissipation of heat through the walls might occurr at a slower rate if working in an oven.

Any experiences to share, or references, that address this issue.

Thanks

[JGK]

We have been thinking a lot about high pressure HPLC in our laboratory.

I am well aware that when you go to very high pressures you have to reduce the diameter of the column to minimize the radial temperature gradients (caused by viscous heating).

Here's my question: How high can you go while still using a standard 4.6 mm column? Can you go to 7000 psi...8000 psi....etc. And how about with a 3.2 mm ID column.

This is important because we are trying to figure out what pressures we can work at without having to take on all the difficulties of extra-column effects.

Thanks

You will be lucky if you can get up to 5000 psi on a conventional HPLC. Backpressure will depend on particle size. Also with some of the older columns and packings you could collapse the stationary phase causing voids and poor chromatography.

I had a method which involved a short 50 mm, 1.7µm column with a mostly (80%) organic MP operating at 0.5 mL/ min. th backpressure was 5200 psi.

I could only get the flow to 0.5 mL/min in 0.1 mL/min stages allowing the flow to equilbrate each step before increasing.

This was done on a Thermo system with a P4000 pump If I had tried it on our Waters system, I dont think it would have handled it.

[oscarBAL]

hello hajdaei,
I would like to know why you want to know about the max. pressuere generated in a high pressure HPLC; according to my point of view if you have one of these instruments; and you use a 5um standart column you will get almost "the same pressure" (may be litlle higher because the delay volume) than using convencional HPLC; if you want to go a higher flows; probably you will get shorter Rt; but your resolution will decreas and your pressuere will increase. Besides as JGK said your column will colapse.
I Think that your pressure will increase only if you increase the flow; but if you do that then you going to loose resolution using an standartd column.
If you use a column with 1.7 um your pressure will increase even to a lower flow compared with a standart column; BUT your Rt will be shorter and your Resoltion will be higer.

when you write standard columns you means 5 and 3.5 um particule size?

Thanks.

Oscar

[HW Mueller]

The higher resolution of UPLC is due to smaller particles, not to higher pressure. The higher pressure is needed to push the liquid through the smaller particle bed.

[Kostas Petritis]

I will add that you can achieve higher resolutions due to just longer columns instead of smaller particles. We pack 65-70 cm capillaries with 3 um particles for our in-house proteomics experiments...

[hajdaei]

Thanks for all the feedback. But the main point of my question was simply that we would like to take advantage of smaller particle diameters and higher flow rates, without getting into excessive pressure ranges.

So maybe we would use a 2.2 um particle and work at 2x the optimal flow rate (instead of a 1.7 um particle and 3x the optimal flow rate).

For this reason I was asking at what pressures do the viscous heating issues start to kick in. And you have to go to 3mm diameter....then 2mm....etc.

And how does heating of the column effect this.

Thanks

[Bryan Evans]

Here are the recommended flow rates for Imtakt's 3um and 5um:

Recommended Flow rates for our 3 micron columns:
ID mL/min
1 0.03-0.2
2 0.1-0.6
3 0.2-1.0
4.6 0.5-2.0
10 2.0-4.0

Recommended Flow rates for our 5 micron columns:
ID mL/min
1 0.03-0.3
2 0.1-0.8
3 0.2-1.2
4.6 0.5-3.0
10 2.0-8.0
20 9.0-20.0

[Uwe Neue]

I am not sure why you are worried about viscous heating. It does have some small effects already at 300 to 400 bar, but even at 1000 bar the effect on performance is small.

Increasing the mobile phase temperature does not reduce these effects. The pressure at the minimum of the van Deemter curve actually increases slightly, when you increase the temperature. The effect is small, but you definitely do not get a pressure advantage from an increase in temperature.