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LC Tubing & Fitting Choices

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Tubing is a fact of life for all HPLC and UHPLC instruments, but making sure you have the correct tubing and fittings for your instrument and application is important.  For tubing and fittings, matching your material type and inner diameter (ID) to the work you’re doing will help make sure you have the safest, most efficient analysis possible. 

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Hi everyone, thanks for joining us for this Restek Tip. Our topic today is tubing and fittings for LC systems.

Now, I'm sure you're familiar with both PEEK and stainless steel, so let's start out talking about PEEK tubing. This is used for pressures up to about 5,000 psi, and you may have experienced what happens if you get beyond this limit. The tubing will release the fitting with an audible popping sound. You'll have a leak somewhere, and you notice your system pressure drops to zero. So, if you're running a sample, and have an unexpected loss in pressure, the first place to check are the connections at your column or at your mixer, just to make sure that none of these fittings have come loose. Now, there's two typical diameters of tubing used for LC systems. The first is a 0.3 millimeter with a blue band, and these are general-purpose connections for your pump to your mixer, the mixer up to the autosampler, and sometimes the autosampler out to the column. Another diameter most commonly used is a 0.13 millimeter with the red stripe, and this is used for connections from your column to your detector, and the small ID keeps the peaks in a tight band, so that helps you get a little better signal and a better detection limit. Now, it's really important to use PEEK fittings when you're using PEEK tubing, because if we use a metal fitting, the temptation is to overtighten, which will crimp that smaller inner diameter, cause some restriction, and could eventually completely block the flow of mobile phase.

Now, if you're running above 5,000 psi, or have a UHPLC system, you always want to use stainless steel tubing, and they come in the same dimensions and the same color codes as the PEEK, so it's very easy to transfer between systems. Now, you might be tempted to cut your own stainless-steel tubing, but we don't recommend it, because it's really hard to get a nice, square cut and to remove all the burrs from the cutting process. By having a really nice, clean, square cut, you can seat the tubing into the port properly, reduce leaks or places where sample can build up and cause carryover in between runs. As far as fittings go for stainless steel tubing, we recommend the EXP type. This has a metal nut and a ferrule with a polymer cone that fits into the port, and a metal portion that connects to the nut.

So, no matter what type of system you have, we've got the tubing and the fittings that'll keep you up and running. Thanks for joining us, and stay tuned for more tips from your friends at Restek.


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