Limits for Retention Time

Chromatography Forum: GC Archives: Limits for Retention Time
Top of pagePrevious messageNext messageBottom of pageLink to this message  By BRStudy on Tuesday, May 13, 2003 - 06:27 am:

Dear Friends;

1 - Is acceptable use in any Residual Solvents Analisis by GC-HeadSpace with DB-624 (30m 0.53mm 3um)column, carrier gas H2 and FID detector one solvent at 0.52 min?

Look my results:
Solvent Rt(min)
1 0.52
2 2.20
3 3.20
4 3.98
5 5.12

Should I improve the retention of my first peak (Solvent 1)?

2 - Are there minim (low) limit to Retention times in GC?


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Anonymous on Tuesday, May 13, 2003 - 06:34 am:

Dear BRStudy,
Without knowing the carrier specifics like velocity cannot tell exactly. It would seem though that this peak is at the void volume of the column and really should be moved back some.

Regards,
Mark


Top of pagePrevious messageNext messageBottom of pageLink to this message  By BRStudy on Tuesday, May 13, 2003 - 08:42 am:

Hi Mark;

Tank you for your help.

1 - But are there limit for linear velocity for 30m 0.53 mm 3um GC-column?

2 - Are there minim (low) value for Capacity Factor (k') for GC-peaks?


Top of pagePrevious messageNext messageBottom of pageLink to this message  By DaT on Wednesday, May 14, 2003 - 02:11 am:

I am not THAT experienced, but just an idea here:

If you switch to N2 as carrier gas instead of H2, can't u go to a much higher flow for your carrier gas then? (I assume with H2 u keep the flow low to keep it "safe", don't know what regulation there is for H2 use as carrier gas)

I think the limit is your patience basically and whether a long time is worth the wait = is the method practical.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Anonymous on Wednesday, May 14, 2003 - 05:23 am:

What is important is that you separate all your analyte peaks from anything else that MAY be present in your samples.

Usually it is wise to have your k' from at least 2 upto 8 or so.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Anonymous on Wednesday, May 14, 2003 - 01:11 pm:

What is the retention of a sample of methane on your column using your operating conditions? You probably want your solvent to be help up longer than that. Otherwise, I agree with the last posting. What really matters is the quality of your separation.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Anonymous on Thursday, May 15, 2003 - 01:15 pm:

Based on solvent peak you are flowing at least 30m per 0.52 min or about 6000cm/min or 100cm/sec or about 5X the optimal flow rate [about 20cc/min(?)].

Are there any peaks that CAN be present near the solvent peaks you are measuring?

Are there any degradation peaks near the solvent peaks you are measuring?

Your first peak has a k' between 3-4. That is acceptable in my book.

Anonymous of Wednesday, May 14, 2003


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