|Why are short sample lines recommended in gas detection?|
Why are short sample lines recommended?
A colleague of mine advised me that I should try to keep the sample lines as short as possible. He said it is essential in detecting acid gases. Of coarse the length of sample line is important in regard to the delay time but he said it has also something to do with the adsorption. Strange because I know PTFE does not adsorb or react with the gas.
You are right PTFE does not react with the gas. However what is happening with most of the acid gases (gases like e.g. HF and HCL) is that they have a tendency to stick on the inside of the sample line. Depending on the humidity in the environment they will form a small layer on the inside of the sample tubing. Test have revealed that 20 meters of PTFE sample line can create a loss of 28% when transporting 14 ppm of HCL. For this reason Bionics Instrument recommends short sample lines for gases like HF and HCL. Sample line lengths of 1 or 2 meters are recommended. An alternative is to use a diffusion type detector.