Chromatography Forum

Hi again

Since u could help me the last time, i want to ask u about the best conditions for the detection of hydrogen.
At the moment i use the following conditions:

Column Temp.: 150°C
Column Flow: 30 mL/min

when i have concentrations lower than 0.01 vol% of H2 its impossible to destinguish between the background noise and the hydrogen peak.

may be u have some ideas of how to reduce the background noise and how to increase the h2 peak, respectively.
that would be great!!!
thank you!

here are some more details:

Detection mode: TCD

carrier gas: Nitrogen

my injection volume is usually 200µl.

here are the informations about the column:

Name: RT-Msieve 5A, Thickness: 10 µm, Lenght: 30 m, Diameter: 0.53 nm

The GC i'm using: GCMS-QP2010 Series (by Shimadzu)

Opfer,

At the risk of sounding like a broken record, and publicly disclosing that I make one of these, I would suggest you consider using an HID. Will easily be able to see 10-100 ppm of hydrogen and would do the oxygen to boot. The only disadvantage is you have to run with helium carrier which can be pricey.

Failing to convince you of the wisdom of that approach, I would suggest you grow your loop size but keep in mind there are some diminishing returns to this process. You want to sweep the loop fairly quickly and at PLOT flow rates this starts to become an issue with loops much above a mL or so in volume. Keep your TCD temp as low as possible as well but hot enough to make sure nothing sticks.

Best regards.

hey AICMM, to be honest, i have no idea what HID is...
moreover i have to come along with the stuff i actually have got.

is it in principle a good thing to use high column temperatures? or should i prefer lower temperatures. i dont really know whats the effect of the temperature, but my spectra look better at high temperatures...

Are you splitting the injection volume or injecting on column?

The issue is the detector temperature not the column temperature per se.

AICMM is correct about using a Helium Ionization detector or a pHID.

But you can detect lower levels and inject a larger sample if you use a micropacked column with your TCD.

Lowering the flow will also increase your sensitivity with a TCD.

Good luck.

Rodney George
consultant

At the moment i use the following conditions:
Column Flow: 30 mL/min
Column: RT-Msieve 5A, Thickness: 10 µm, Lenght: 30 m, Diameter: 0.53 nm

Forgive me, I've been out of the GC field for a while and am having to play "catch up" with my knowledge base but, is that flow correct?

I've also assumed your column diameter is mm and not nm or the film thickness would be 19,000 x greater than the diameter.

You could easily go to 500uL or even 1ml sample loop.

Opfer,

I would be happy to send you more information about HID's if you want to contact me at aicmm at flash.net

Could you also post all of your flows? Column, split, reference, make-up?

Best regards.

My 2c 0.01% is by my calculations 100ppm, generally the MDL (Minimum Detction Limit) for using TCD. You can tweak things to get down below that but you will be struggling. As you list the system as GC/MS can you use the MS as a detector, Thermo quads scan from 2-1023 so anyone tried it for Hydrogen ? You refer to spectra rather than chromatograms ?? Certainly more sensitive for other compounds but Hydrogen ??
Column flow , way too high for good retention and separation, OK for good sample transfer from loop and TCD. Not suitable for MS. Hydrogen is not going to retain much even on a Molsieve column.

For ppm and lower level detection the proper solution is HID/pHID there are plenty of us suppliers out there