GC Manual vs Valve injection, what’s the biggest differences

[Kanokrat]

Hello,

I have injected atmospheric level of CH4 and CO2 gas standard, using both manual and valve injection, experiencing that the retention time of manual injection is much longer (the run time was 7.5 min for loop injection but it’s changed to longer than 30 min for manual injection).

The 10 ml of sample was injected manually and a 2 ml gas sample loop was used earlier.


Why is such a huge difference of retention time? Is there anything suspicious going on here?


Appreciate your suggestions:)
Kanokrat

[70 eV]

Sounds like the GC method parameters are not the same. Check your oven ramp settings.

[Marino]

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[Kanokrat]

I have checked the gc method, it is exactly the same as before. Is it possible that there is a huge leak that cause the problem?
So far I have increases the column flow rate, to minimise the retention time. Is okay to remain leakage?
Is it alright to inject 5 ml to 1 mm id with 100/120 inside?


Cheers,
Kanokrat

[AICMM]

Kanokrat,

Nowadays, 10 mL injection volume is huge! What flow rate, what type of column are you using?

Remember your peak can never be narrower than the injection band width so if you take a significant amount of time for 10 mL the peak will be wide.

Does not, I recognize BTW resolve the question of retention shift but would need more data to make some sort of stab at that problem.

Best regards,

AICMM

[Kanokrat]

Hi AICMM,


The problem now has been solved. The issue was there was a huge leak at the inlet. Also, I have changed the injection volume to 1 ml and it works perfectly well. However, manual injection is poorer than GC valve.

Thank you.

Kind regards,
Kanokrat