PEEK Tubing is commonly used in a variety of engineering, manufacturing, and pharmaceutical environments (such as liquid chromatography/HPLC). It has become a standard item in the operation of many HPLC systems. It is convenient, inexpensive, and easy to identify the internal diameter. PEEK tubing can replace stainless steel, titanium, PTFE, or Tefzel tubing. It is less oxygen permeable and more temperature resistant than PTFE or Tefzel tubing, and should be used with PEEK fittings.
One favorite PEEK Tubing supplier is LEAP PAL Parts – they provide high quality tubing, and generally will give you a discount if you call or email them. PEEK tubing can also be bought on Fisher Scientific from a number of different vendors.
PEEK tubing is made from PolyEther Ether Ketone (hence the name PEEK), which is a colorless organic thermoplastic polymer in the polyaryletherketone (PAEK) family. PEEK is a semi-crystalline thermoplastic with great mechanical and chemical resistance properties that are retained even at high temperatures (up to 500 ° F), making it the perfect choice for a variety of applications – including High Performance Liquid Chromatography.
PEEK emits little smoke or toxic gas when exposed to flame. This material is tough, strong, and rigid and has superior creep resistance. It also resists radiation and a wide range of solvents. With its resistance to hydrolysis, PEEK can withstand boiling water and super-heated steam used with autoclave and sterilization equipment at temperatures higher than 482° F. Typical applications for PEEK include the automotive, marine, nuclear, oil-well, electronics, medical and aerospace industries.
PEEK tubing has become a popular replacement for stainless steel tubing in various places in the HPLC system. It is especially useful when contact between the sample and metal components must be avoided, such as when working with metal complexing agents or certain biochemical compounds.
The sheathing polymer (polyetheretherketone) is mechanically strong and has ideal characteristics for sealing with conventional metal or polymer ferrule systems.
PEEK tubing has a very smooth internal surface, which causes less turbulence than similar sized metal tubing. Turbulence can cause remixing of separated sample bands and dilution of bands by the mobile phase during HPLC.
PEEK tubing may be used as a direct replacement for conventional stainless steel tubing used in liquid chromatography systems.
PEEK acts as an excellent alternative for stainless steel tubing in high pressure applications and analytical systems. Its mechanical properties allow it to be used in many situations where stainless steel would become too reactive. Unlike stainless steel, PEEK tubing is flexible and can be easily cut into preferred lengths with a special cutter. PEEKs internal surface is much smoother than that of metal tubing, thereby reducing the risk of dilution and remixing of samples.
PEEK tubing offers outstanding solvent compatibility, with very few solvents interacting negatively with the polymer. It is also flexible and has excellent mechanical stability.
Another advantage of PEEK is that it is easily cut to any desired length with a small guillotine-like cutter containing a razor blade. But be careful not to cut the tubing by slicing through it like you would with a pair of scissors – this can block the lumen of the tubing. Rather, pinch the cutter and rotate it around the tubing until a groove is cut all the way around the tubing. The tubing then can be snapped at the cut, leaving the lumen open. As with SS tubing, it is wise to run a few milliliters of solvent through the tubing to purge any particulate matter left from the cutting process. Just connect the up-stream end of the tubing to the HPLC system and turn on the pump for a minute or so.
One nice characteristic of this tubing is that it can be connected with finger-tightened PEEK fittings. These allow tool-free assembly for convenient connections. Because the connection is less secure than a SS fitting on SS tubing, proper assembly is mandatory. With the pump off, push the tubing to the bottom of the fitting port, then tighten the nut. If the fitting leaks, turn the pump off, loosen the nut, reseat the tubing, and tighten the nut. Attempting to tighten the nut with the pump on can cause the connection to slip, creating leaks or internal voids. Also, although you can use PEEK fittings with SS tubing, don’t try the reverse. SS ferrules can pinch PEEK tubing closed or if over-tightened, can cut off the tip of the tubing.
PEEK tubing is color coded by most manufacturers for easy identification of the internal diameter. Many labs worry about the color leaching out and causing UV interferences. However, several laboratories have done extensive testing and did not find any evidence of problems with extracted pigments. If this is a worry for your lab, there are several options available such as Natural PEEK Tubing, Dual Layer Color Coded PEEK Tubing, and Striped Color Coded PEEK Tubing. The latter three types of tubing separate the color / dye from the inside of the tube to avoid any concern of a sample stream being contaminated by pigments used in color coding. Natural PEEK Tubing of course contains no dye whatsoever.
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PEEK Tubing can have a few disadvantages. Not all HPLC solvents are compatible with PEEK tubing. Aqueous buffers and salts are fine, as is acetonitrile (ACN), methanol (MeOH), and other alcohols. But tetrahydrofuran (THF) and the chlorinated solvents are not recommended for PEEK tubing. These solvents weaken the tubing and cause it to become brittle. DMSO, methylene chloride, and THF can cause mild swelling of PEEK polymer. Concentrated nitric and sulfuric acids will degrade PEEK. However, some studies show it can safely withstand 20% – 30% nitric acid at room temperature for brief system cleaning – just be sure to remove your column prior to cleaning.