In an amazing TED-Ed video from Matt Anticole, the wild history of the metric system is explained as a very smart cartoon. Matt concluded his video with a rather positive message for the scientific community: “Nevertheless, the metric system is almost universally used in science and medicine.” It sounds great, but the key word here is almost. And you already guessed right… the world of chromatography is one of these dark alleys of science where both systems are still going along.
And it is especially true for tubings and connectors in your HPLC system.
HPLC Tubings and Color Coding
In every HPLC lab, you will find tons of different tubings with different color codes. At least the outer diameter (OD) is mostly standard at 1/16’’ for HPLC tubings. In order to fit to different set-ups, the inner diameter can vary – and the colour codes are here to help identify the right tubing. Typical values vary from 0.005’’ to 0.020’’, and the fun begins when you have to determine the volume of tubing in your system – as a matter of fact in metrics SI units! But here at least you can cheat.
If you have to connect your chromatography system to other equipment, this is where the nightmare goes up onto a higher level. I once had an experiment in which I needed to connect an HPLC pump to a continuous micro-reactor. The tubing coming from the pump had been chosen a little big bigger for this experiment – but still in English units as usual for HPLC tubings, 1/8’’ OD – and the micro-reactor had specific connectors which seemed to fit tubings with the same OD. The nuts and ferrules were fitting well, and I started the pump… I had to immediately break up the experiment, clean up my bench and find a work around to connect my pump with my reactor. 1/8’’ OD converted to the metrics system is 3.175 mm, and the reactor was made for tubings in the metric system – 3.0 mm exactly. A difference of the thickness of 2 hairs…
And you’re not alone: a simple unit conversion error between English and metric units made by people from two different systems engineering teams – Mars Climate Orbiter spacecraft team in Colorado and the mission navigation team in California – led to the total loss of the spacecraft even before the real mission began. The orbiter just missed the orbit.
“The peer review preliminary findings indicate that one team used English units while the other used metric units for a key spacecraft operation. This information was critical to the maneuvers required to place the spacecraft in the proper Mars orbit.” states the NASA on its own web site.
So, the next time you start swearing about having to convert units from one system to the other, or you have to clean up your lab bench because of a connector leakage, just think about the poor guys at the NASA. In the end, your unit conversion issues are not so bad, are they?