Chromatography Forum

I am wondering what is the typical Helium detection limit by GC-TCD. The method I am using: Agilent 7890GC with a TCD. Column: packed molsieve 13x column; carrier gas: Ar; Oven temp: isothermal @30°C; flow rate: 30ml/min. TCD temp: 200°C. Sampling size: 5ml.

With this method, I am able to achieve a LOQ approximate 5ppm, is this a reasonable limit for He or do I have some room to improve the sensitivity? I am use to seeing ppb level of other gases (such as Ar, N2, CH4 etc) analyzed by GC-PDHID.

Looking forward to hearing your comments. Thank you!

Low ppm for any gases is good sensitivity for TCD as you have seen an HID is much more sensitive

You might (heavy emphasis on the might) be able to get it down to 1-2 ppm, but 5 ppm is not bad. Try balancing your measuring/reference cell flows; this might help a little. You might get a slightly sharper peak with nitrogen carrier; make sure you're running at optimum flow.

TCD just isn't a very sensitive tool, unfortunately.