Three chromatography system parts and why they are important

Underneath the clothes of your chromatography unit lies a delicate network of chromatography system parts that we barely pay any attention to. With this blog post, I hope to change this, by highlighting fittings, hoses & tubes and ports as essential system components for your flash chromatography and prep HPLC applications. Read on to find out more about these chromatography system parts and how to install and use them best.

My wife and I received an espresso machine for our anniversary a few years ago. It’s a lovely and very useful gift, but it broke down last week. Luckily, the machine is still under warranty, so a repairman came to fix it. He quickly disassembled the system as I snuck a look into what he was doing. I was astonished into how many system parts were inside. Boilers, pipes, valves, pumps, it really took an intricate network to deliver my morning brew.

I thought about how all instruments require such a delicate connection of system parts to function. From TVs to cars to, of course, lab equipment. I mean, have you considered what it takes for your chromatography system to deliver your chromatograms day after day?

If not, well, I have. And since we are on the topic, I think it’d be a great idea to discuss some chromatography system parts that are absolutely essential to the performance of your unit.

1. Chromatography system parts: Fittings

As I’ve already discussed with you in a previous post , general system fittings look as follows:

chromatography; flash chromatography; prep HPLC; preparative HPLC

The design can be either one piece where a nut and ferrule are combined or two-pieces, with a separate nut and ferrule. A one-piece design is easier to use and only needs to be hand-tightened. A two-pieces design offers more options and flexibility. It can be either wrench tightened when made of steel material or hand tightened when made of PEEK, FEP, ETFE or PTFE material. Both designs can be used for low pressure applications, such as flash chromatography or high pressure (prep HPLC) applications.

Here, I should offer you a few more insights into the materials that make up these chromatography system parts.

  • Steel – is a high strength material, resistant against any solvent, hence it is typically used for extremely high-pressure applications, such as prep HPLC. Steel fittings can be used only once, as they only fit into the port they have been swaged onto
  • PEEK – is high-thread-strength material, resistant against most solvents, except for concentrated acids and chlorinated solvents. This material is suitable for high-pressure applications such as prep HPLC. The material is biocompatible and ideally suited for applications where connections are changed frequently (such as prep HPLC and flash chromatography)
  • FEP/ ETFE / PTFE – this material has less thread strength but is resistant against any solvent and is biocompatible. The material is well suited to low pressure applications, such as flash chromatography

The ferrule

The ferrule of your chromatography fitting can be either flat-bottomed or coned:

chromatography; ferrule; flash chromatography; prep HPLC; preparative HPLC

Flat bottom ferrules are suitable for low-pressure applications, such as flash chromatography. They are not permanently attached to the tubing and those nose of the ferrule faces the nut. Coned ferrules are more suitable for high-pressure applications, such as prep HPLC. These types of ferrules are permanently swaged onto the tubing. The nose of the ferrule faces away from the nut.

The nut

The nut can be described with English style with a diameter of ≥1/4, gauge for ≤1/4 and a number of threads. Alternatively, the nut can be described via metric style with a diameter in millimeters and number of millimeters per thread. Bigger diameters (1/4-28) are used for applications with higher flow rates (flash chromatography) to reduce back pressure. More threads (10 -32) can resist higher pressures and preferred for high-pressure applications, such as prep HPLC.

The nut head can be either a Knurl head, which needs to be finger tight or Hex head, which is commonly made of steel only and needs to be wrench tight.

2. Chromatography system parts: Hoses & Tubes

The biggest difference between hoses and tubes is that hoses are flexible, whereas tubes are rigid. The internal diameter (ID) and lengths of these chromatography system parts influence back pressure and dead volume, which in turn affects peak shape. Common internal diameters are 0.08” for flash chromatography and 0.02” for prep HPLC applications. Common outer diameters are 1/8” for flash applications and 1/16” for prep HPLC applications. The length of the hoses and tubes depends on the application. The longer these chromatography system parts, the more back pressure and higher dead volume we see.

3. Chromatography system parts: Ports

Ports are available for different nut sizes. For example, 10 – 32 for coned and ¼-28 for flat bottom nuts. Ports can be flat-bottomed, where the nose of the ferrule faces away from the port. These types of ports are suitable for low pressure applications, such as flash chromatography. The ports can also be coned, where the nose of the ferrule faces towards the port. Coned ports are appropriate for high pressure applications, such as prep HPLC.

Now that we’ve looked at three chromatography system parts, the fittings, hoses and tubes, as well as ports, let me offer you a few tips on how to set them all up to achieve maximal efficiency.

  • Ensure all hoses and tubes have a straight cut and the edges are free of any residues before installing them to any chromatography system
  • Always use the appropriate tools for cutting the hoses and tubes
  • The Knurl head nuts or fittings should only be tightened by hand
  • Overtightening the nuts or fittings will typically reduce the inner diameter of the hose and lead to higher pressure and wrong flow rates
  • Hex head fittings are typically used with stainless steel tubes and must be installed by hand for the first time to avoid damaging the threads. At the end these must be tightened (typical ¼ turn) using an appropriate wrench.

Now that you have woken up and smelled the coffee, maybe you are interested in even more information on chromatography system parts. In this case, download this free factsheet on chromatography system parts or watch a lovely video on the topic:

and learn even more about these important system components.

And yes, my espresso machine works again, it was a problem with the fittings😊!

Till next time,

The Signature of Bart Denoulet at Bart's Blog