Chromatography Forum

Dear friends,
I am working on one method but having problem to execute it and meeting system suitability
Method is
Column:- DB-1701 30m X 0.25mm 1.micron
temp:- 50 Deg 5 min - 10 Deg/min -200 deg
Detector Temp:- FID - 250 Deg
Injec Temp:- 25 Deg
Gas :- Helium @ 10 psi
Inj Volu :- 3 microlit

Problem :- Unable to achieve RSD lmit 2.0 % for 5 std Injections.

Please help me

what solvent, why so low injector temperature ?

isn't your column overloaded ?

what mode of injection ?

Your problem could be as simple as the type of injection liner or the placement of the column in the injector.

Much more information is needed before anyone can perhaps determine the issues involved.

best wishes,

Rod

what solvent, why so low injector temperature ?

isn't your column overloaded ?

what mode of injection ?

Solvent :- Ethyl Alcohol
Yes! column is overloaded due to sample injection.
Mode of Injection is Split - split ratio is 100:1 on Thermo Focus

Your problem could be as simple as the type of injection liner or the placement of the column in the injector.

Much more information is needed before anyone can perhaps determine the issues involved.

best wishes,

Rod

Dear Rod
Split Liner 5 mm and the distance is 4 cm in Injector port

Please help

Thanks

Solvent :- Ethyl Alcohol
Yes! column is overloaded due to sample injection.
Mode of Injection is Split - split ratio is 100:1 on Thermo Focus

In my opinion you have to avoid column overloading by analytes (not solvent).

I don't know what is "Thermo Focus" - is it a kind of PTV ?

If it is common split inlet than your inlet temperature is substantialy to low.

" If it is common split inlet than your inlet temperature is substantialy to low. "

I agree. Try 80C as a minimum and go up from there.

Rod

BTW - you split your sample 100:1 so probably column is not overloaded - depends on concentration of analytes.

The very low inlet temperature has already been commented on - to get that low you must have cryogenics in the inlet, which suggests that it is a PTV of some kind, but if it is you need to programme its temperature after the injection.

Why inject 3 ul and then split 100:1, why not inject 1 ul and split 30:1 ?

Peter

Check condition of autosampler syringe.
Are there bubbles in syringe when drawing samples ?

1 µL injections will be more reproducible than 3 µL (less bubbles).

Solvent :- Ethyl Alcohol
Yes! column is overloaded due to sample injection.
Mode of Injection is Split - split ratio is 100:1 on Thermo Focus

In my opinion you have to avoid column overloading by analytes (not solvent).

I don't know what is "Thermo Focus" - is it a kind of PTV ?

If it is common split inlet than your inlet temperature is substantialy to low.

I am realy very sorry , Injector Temp is 250 Deg C and Thermo Focus is make of GC.

Check condition of autosampler syringe.
Are there bubbles in syringe when drawing samples ?

1 µL injections will be more reproducible than 3 µL (less bubbles).

These actions I already takeup while performing the analysis.
I also tried to inject 1 µL Injection but required limit is still not achieved.
Is there any other problem? Please help me.

I suspect you are trying to inject too much sample, or your column is misalligned in the injector. 2% RSD for split injections is about the norm.

What is your split ratio? Rather than injecting 3 microliters, why not do splitless?

You really need to tell us more about the sample. What is the type of liner beside ID, (there are many kinds) ?

good luck,

Rod

Injecting 3 ul of ethanol to a hot inlet gives a very large vapour cloud, a pressure pulse and disrupted flow and split ratio. As suggested before; decrease you injection volume to 1 ul and change you split ratio to 30:1 (you say that you did 1 ul injections, but did you decrease the split ratio ?).

Do you have to use ethanol as the solvent ?

Peter

I think at normal conditions, injection volumn in a GC is 2.0 microliter max. There maybe a backflush and that could affect the RSD%.