How Tubing Can Improve Your Chromatography
If you’re a chromatographer, then it’s probably safe to say that one of your daily goals is to achieve great chromatographic results – chromatograms that feature well-resolved peaks with little-to-no band-broadening and a flat baseline…the kind of results that make your job easier and headache-free. To achieve that goal, you likely spend a lot of time on method validation, operational protocol, calibration, mobile phase preparation, and the like. Interestingly, what chromatographers sometimes overlook is the impact that the fluid path connections can have on the quality of the results obtained.
Fluid path connections are essentially comprised of two main components: the flow path tubing and the compression fittings. In this post, we will hone in on the flow path tubing and how to best prepare it for use in your system’s flow path.
• Choose the Best Inner Diameter & Length – One of the most important things that you can do with regards to the tubing you choose is to select the best inner diameter and length of tubing to pair with your application.
With regards to length, a good rule to follow is this: Keep your tubing as short as functionally possible. The tubing comprises the majority of the fluid pathway in the system. This means that longer lengths of tubing will create longer delays for gradient changes to reach the column, which can force your separations to take longer than necessary. Also, longer lengths of tubing force the sample components to remain in contact with the mobile phase for a longer period of time, which can lead to dilution of the sample and thus band broadening, which can lead to poorly resolved sample components, etc. Keeping tubing lengths as short as possible helps minimize the duration of time the sample is exposed to the mobile phase and can therefore help provide you with quality chromatographic results.
Another important thing to consider is the impact of tubing inner diameter on the results you obtain. Because the volume of the tubing is proportionally related to the square of the internal radius, that means the tubing inner diameter can have a dramatic impact on the residence time for the sample components in the flow path. For instance, if you use the standard .010” (~0.25 mm) inner diameter tubing as a “baseline” for tubing size, then simply changing to .005” (~0.13 mm) inner diameter tubing reduces the internal volume to ¼ of the volume in the larger inner diameter tubing. This results in an increased linear velocity, allowing the sample to reach the column more quickly, and the separated components to reach the detector more quickly as well. It also reduces the zone of interaction between the mobile phase and the sample components, thus reducing band-broadening effects as well as improving chromatographic results overall.