Helium Detection Limit by GC-TCD

[1000H2O]

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!

[CE Instruments]

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

[mckrause]

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.