What Types of Fittings Are Used in HPLC?

There are two types of fittings commonly found in all HPLC systems. Low-pressure fittings are used to make connections up to the inlet of the HPLC pump, and high-pressure fittings are utilized to make the connections from the outlet of the HPLC pump and throughout the flow path until the detector. The plumbing from the detector to the waste collection system, once again, uses low-pressure fittings.

Fittings are an inexpensive HPLC supply, but they’re crucial to an HPLC system. If the incorrect fitting is chosen or the fitting is not made correctly, they have the potential to wreak havoc on your HPLC system. Experienced chromatographers understand that plumbing their HPLC system with good connections is imperative for success and minimizing frustration in the lab.

Flangless Fittings Are Chrom Tech’s Most Popular Low-Pressure Fitting

Low-pressure fittings are utilized in the flow path between the solvent reservoir bottle and the pump’s inlet. Most often, these HPLC fittings are ¼-28 Flat Bottom Flangeless Fittings. Many years ago, before the introduction of flangless fittings, scientists had to learn how to use a flanging tool and flange the tubing prior to using low-pressure fittings. Thankfully, flangeless fittings eliminate the need to flange tubing. This removable and reusable system boasts several benefits, such as providing flangeless chromatography fittings for observing mixtures and solvents. Flangeless fittings are easy to use. Just slip the nut and ferrule over the tubing and finger tighten the assembly into your receiving port. Our flangeless fittings require minimal downtime because component replacement is quick—it takes only a few seconds. Flangeless fittings systems typically require only one new ferrule at minimal cost when repairing a connection.

Other Low-Pressure Fittings

Other common low-pressure fittings used in HPLC include luer adapters or barbed adapters. Luer adapters have a female or male luer on the side of the connection, while the other side typically has a male or female thread. One example would be to economically prime an HPLC pump. Simply remove the 10-32 fitting on the outlet check valve (standard on most pumps), insert a female luer to 10-32 Coned Male Fitting (P-642), attach a disposable plastic luer syringe, and draw the mobile phase through the pump head.

Barbed adapters connect the tubing’s internal diameter to a male threaded connection. We typically see barbed fittings when plumbing the detector outlet to the waste containment system. If you have ever been written up by safety for not having a good waste system, read about Chrom Tech’s Solvent Waste System. For a similar price to an HPLC column, you can have a closed HPLC waste system that will satisfy your company’s (or local jurisdiction’s) safety requirements.

10-32 Coned High-Pressure Fittings

10-32 threaded coned fittings are the most common high-pressure fittings in an HPLC system. These can either be fingertight (typically polymeric) or wrench tightened (typically stainless steel). First, we will explore the wrench-tightened high-pressure fitting. To properly make a wrench-tightened high-pressure fitting, it would be advantageous to have a third hand, which many of us don’t have! Below is an excerpt from the Idex-HS All About Fittings Guide by John W. Batts, IV.

The most demanding fluid connections are typically found in the high pressure areas of a system — in fact, it’s not unusual for pressures in HPLC to reach and exceed 4,000 psi (276 bar) and in UHPLC to reach pressures of 15,000 psi (1,034 bar) and higher! Because these connections experience the largest amount of stress, let’s focus first on how to make good high pressure connections. One of the most popular styles of connections used for HPLC and UHPLC high pressure fluid pathways is a “swaged” connection. We briefly mentioned the concept of swaging earlier. Now, let’s look at the process of swaging a little more closely — what it is, how it works, and why it remains so popular today. First, as a recap, swaging means “permanently” attaching a ferrule to a piece of tubing, typically in a high pressure application. Often, both the fitting and the tubing are manufactured from some form of stainless steel, although that doesn’t always have to be the case. However, swaging typically will not involve an all-polymer ferrule. Most people who are swaging are using stainless steel ferrules as part of the fitting system.

In order to swage a ferrule onto a piece of tubing, slip the nut over the tubing being connected. Follow that by slipping the ferrule over the tubing, just below the nut, ensuring the tapered nose of the ferrule is facing away from the nut (remember the little poem from page 13?). Once the nut and ferrule are in place, insert the tubing into the receiving port until the tubing butts up against the bottom of the port. Please Note: This process works for most ports; however, some ports do not have a solid stop against which the tubing can rest. For these, extra care is necessary to ensure the tubing remains extended past the ferrule’s nose...but not too far! With the tubing held in place, fingertighten the nut completely, and then wrench-tighten it another 3/4 turn. This often will complete the swage, crimping the ferrule onto the surface of the tubing. To make sure this has been done correctly, loosen the assembly and remove it from the receiving port. Inspect the ferrule to ensure it will not come off; if it’s still loose, reinsert the fitting and tubing assembly into the receiving port and tighten in 1/4-turn increments, checking to see if the ferrule has been fixed onto the tubing after each 1/4-turn.

As described above, making high-pressure connections with stainless steel wrench-tightened fittings can be difficult. Luckily, years ago, another option came onto the market: the fingertight fitting. Fingertight fittings eliminate the need for the wrench (and the third hand!), and some new versions can hold connections up to 1300 bar (18,850 PSI). The original one-piece or two-piece fingertight fittings from Idex-HS (formerly Upchurch Scientific) typically hold up to about 4,000 psi.

Conclusion

Selecting the appropriate HPLC supplies, understanding fittings, and making good connections are imperative for frustration-free chromatography. Thankfully, fitting technology has greatly improved over the past 30 years. If you are having trouble determining which fitting you should use in your system, reach out to Chrom Tech—we are here to help.