Difference in HPLC peek tubing

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Hi everyone,

Just curious how changing the ID of HPLC tubing between 0.005", 0.007", and 0.010" affects peak shape, resolution, and/or separation in the resulting chromatogram?
For isocratic separations, to a VERY crude first approximation, wider tubing will have little impact on peak shape, will degrade resolution (because peaks will be wider) and will have little impact on center-to-center separation. What matters most is the total volume of the tubing relative to the volume of the peaks. If you have a large (e.g., 150 x 4.6mm) column and relatively short runs of tubing (e.g., 100mm or so) you would probably not notice any difference. A short (e.g. 50 x 2.1mm), high-efficiency column would require short lengths of narrow tubing.

The situation with gradients is more complex. Larger tubing will increase the dwell volume (gradient delay volume) and so MAY affect the selectivity (peak spacing). Again, that's more likely to be a problem with short, narrow, high-efficiency columns

0.007" id is generally a good compromise unless you are using very small columns. And keep the runs of tubing as short as practicable.
-- Tom Jupille
LC Resources / Separation Science Associates
tjupille@lcresources.com
+ 1 (925) 297-5374
Agreed. The main influence is often indirect, the result of what the tubing is doing to your back-pressure. For example, if you decide you need to run a semi-prep column on an analytical HPLC, the main effect of the narrow tubing is to add so much back-pressure that you find you can't run it at more than 3 mL/min when you'd rather be running at 6 mL/min or more, and this will affect the chromatography! But over-wide tubing will give you wider peaks, which means lower resolution and also lower sensitivity.

Small differences in bore make a huge difference to back-pressure at a given flow rate because tubing doesn't work like electrical wire. In an electrical situation, the resistance of the wire is created by its entire cross-sectional area, so resistivity is constant. In a tube, the resistance is created by the boundary-layer and surface interactions of the solvent and the wall of the tube (the liquid right in the middle of the tube gets a free ride!), so wide pipes are relatively more efficient, because less of their cross-section is close to a wall.
lmh wrote:
Small differences in bore make a huge difference to back-pressure at a given flow rate

https://en.wikipedia.org/wiki/Hagen%E2% ... e_equation
A bit confused about your question... Are you asking about tubing made of PEEK ? Maybe you were hinting at a question about "PEAKS", which are the detected traces on the chromatogram?

PEEK tubing (and also PEEK fittings) are a polymeric option vs. Stainless Steel (SS) tubing. PEEK tubing is often used in place of SS tubing where bio-compatibility is needed or in ION Chromatography. It can also be used in conventional chromatography, but ONLY when you insure that chemically compatible solvents are used with it (as it is NOT compatible with a number of solvents used in HPLC analysis, such as THF, chloroform, DMF, Methylene Chloride, strong acids/bases etc).
If your question has nothing to do with "PEEK" tubing/fittings and you are inquiring about what changes may occur when using different tubing ID's, well basically back-pressure and delay volume changes. Back-pressure changes are only important if they are near or exceed the total system design max pressure (though with higher pressures you will also have more wear and tear on the system plus internal heating of the solution which may change the chromatography in extreme cases).

    Here is a link to a free article and TABLE on "Backpressure Changes, Pressure Drop from HPLC Tubing Selection (0.007, 0.005, 0.010")"; https://hplctips.blogspot.com/2019/06/b ... -from.html
    Depending on WHERE the changes in tubing ID are made, changes in tubing which result in delay volume changes may change the retention time, peak shape and detection limits. Tubing volume (overall system volume) as with flow cell volume, column volume, injector volume must all be optimized for each application. Understanding how changes made to tubing, connections and the flow path are fundamental to learning how to use an HPLC system to develop methods on.

    "HPLC Capillary Tubing Connection Volumes"; https://hplctips.blogspot.com/2012/10/c ... lumes.html
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