PEEK tubing ID for HPLC

Discussions about HPLC, CE, TLC, SFC, and other "liquid phase" separation techniques.

3 posts Page 1 of 1
Hi everyone.

Which do you think is the best ID for HPLC tubing? I have the chance to buy from 0.003 to 0.010 inches. I know smaller is better but worry about pressure. Is there too much difference?
Q. F. Ignacio Viera
Why use PEEK? Is this a bio-compatible only HPLC system or perhaps an Ion chromatograph?

Your question of "ID" requires more context to make sense of and provide a suggestion. The "best" ID to use will depend on the exact type of HPLC system, the flow rate range actually used (note I wrote, "Actually" because the capable range is less relevant), the fluid viscosity, the sample types and the column dimensions used (because extra column dwell volume may or may not matter for your applications).

The closest thing we have to a generic standard for analytical HPLC systems (over the last 20 years) would be tubing with an ID of 0.17 mm (0.007"). This provides a nice compromise between low internal volume, modest pressure and less likely to clog or plug. For applications where delay volumes need to be minimized, very low volume columns (less than 600 ul) will be used and/or very low flow rates (< 220 ul/min), you may desire to use 0.12 mm ID tubing (0.005"). A warning though that this tubing may be more prone to plugging if care is not taken to flush down the system regularly, filter everything and insure that all samples, additives and buffers are FULLY dissolved at all times in the mobile phase, esp at time of injection.

Here is a link to capillary tubing volumes to illustrate the effect of changing the ID (and the length) of a capillary has on the volume. "CAPILLARY TUBING CONNECTION VOLUMES" http://www.hplctools.com/capvolume.htm

Here is a table of generic HPLC column volumes too: http://www.hplctools.com/columnvolume.htm
In defence of PEEK, it's very easy to use, wherever the pressure isn't excessive (i.e. everything post-column in any system, and pre-column in HPLC applications where you expect pressures not to exceed 300bar). Metal tubing is a pain to cut, and a pain on any system where you make regular changes to the plumbing, because it doesn't like being bent, bent back, fiddled around with and bent again; it just gets more and more kinked until fittings don't fit. The thin metal tubing with normal-diameter ends is easier to use, but liable to breakage at the junction between thin and thick. I haven't tried PEEKsil, but it would worry me that where connections are continuously being changed, it would get compressed, and you can't just trim a few mm off the end, like you would with normal PEEK.

Yes, the previous poster is quite right about flow-rate. For what it's worth, we generally use red (0.005") on nearly all our systems, which are analytical and mostly equipped with UHPLC pumps, with methods running at up to about 0.6mL/min. We do change to 0.007 or 0.010, or even wider, downstream of detectors that don't like back-pressure (breaking fluorescence detector flow-cells is a hobby restricted only to the very wealthy). We have run semi-prep methods at up to 3.5 or 4mL/min on these systems, but the back-pressure isn't pretty, and I wouldn't try it with a viscous solvent mix. In these cases we keep the tubing as short as possible, and use the blue 0.01" where possible. Upstream of the column, everything is inevitably metal.

In the end, you choose the tubing that keeps your backpressure down to what you deem to be acceptable. It's worth having all the standard sizes available in the drawer.
3 posts Page 1 of 1

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