Head Space problem

Chromatography Forum: GC Archives: Head Space problem
Top of pagePrevious messageNext messageBottom of pageLink to this message  By andrzej murdza on Wednesday, August 11, 2004 - 11:10 pm:

I have a problem with my HS 7694 when I run a sample with 0,1g drug + aceton 1000ppm metanol 1000ppm butanol 1000ppm+2ml dimetylsulfoxide +8ml water everything is allright but in the next run (only water) I obtain a chromatogram with peak of dimetylsulfoxide. The same situation is when I analyze a impiurities of ethanol 10 ml ethanol to the vial and in the next run(onaly water in the vial I have a ethanol on my chromatogram.
I replace in my HS many thing valwe loop capilar and other and the problem steel appear.I don't have a leak and I chek up flow vial pressure 15 psi and carrier pressure 22 psi is ok. HELP!!!


Top of pagePrevious messageNext messageBottom of pageLink to this message  By anonymous on Thursday, August 12, 2004 - 02:02 am:

Hi,
Did you try to "isolate" you GC running without your headspace (to check if it's you GC or you headspace)?


Top of pagePrevious messageNext messageBottom of pageLink to this message  By andrzejmurdza on Thursday, August 12, 2004 - 02:30 am:

yes i tray to do it and my GC is ok


Top of pagePrevious messageNext messageBottom of pageLink to this message  By chromatographer1 on Thursday, August 12, 2004 - 05:42 am:

YOu probably should clean your HS sample loop and the transfer line. You should use deactivated lines for both. You would get better results if you used less sample than 10mL of carrier solvent but that is another issue.
The rotor can absorb solvents but I suspect you have had excessive deposits in your transfer line built up over time, that and your transfer line temperature is too low and you are coating the line with DMSO which acts like a trap.
Be certain your purge flow on the transfer line is adequate also. Good luck.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By andrzejmurdza on Thursday, August 12, 2004 - 10:02 pm:

I do it what you say but coud you help me and say how can I check my purge flow


Top of pagePrevious messageNext messageBottom of pageLink to this message  By carla on Sunday, August 15, 2004 - 02:47 pm:

maybe you have just overload your column? you can try an old and stable method to check this.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By andrzej murdza on Monday, August 16, 2004 - 01:02 am:

With my GC is everything allright


Top of pagePrevious messageNext messageBottom of pageLink to this message  By GC Dave on Monday, August 16, 2004 - 08:51 am:

Andrzej
On your original posting do you say that you are putting neat ethanol into your headspace vial??!!
And approximately 20%DMSO?
No wonder you are getting carry-over! 1000ppm is very high for solvents - anyone agree?
I think I replied to a similar posting in the last month or so in the same vain.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By andrzej murdza on Monday, August 16, 2004 - 11:11 pm:

Dave
Thanks for your help but I want to say you that i don't have problem with ethanol at value 1000 ppm in next run (water only)I have clean chromatogram it means with out peak of ethanol. I have a problem with DMSO this solvent steel appear on my chromatogram after I run my sample.I think that chromatographer1 have right and I have deposit in my transfer line or in the HS needle because when I done steam cleaning DMSO disappear I don't understending this proces maybe when I use difrent carrier solvent, but the problem is that my sample don't dissolve in water and I cant use DMF


Top of pagePrevious messageNext messageBottom of pageLink to this message  By jchromatographer1 on Monday, August 23, 2004 - 07:07 am:

Andrzej

You have not communicated the temperatures of your vial, the valve needle assembly or the transfer line.

Giving little information means that the folks in the forum have to guess a lot and you may not get the help you need. Try to be a little more open with what you are doing. Headspace hold little secrets for the members of this forum. If you cannot communicate the details of what you are doing, and I understand this, then it is not likely you will get much useful information from those willing to help you here.

The straightforward solution is to run blanks between samples. Yes, not efficient or cost-effective, but sometimes it is what you have to do.

I had to shoot 10 blanks after a sample to remove carryover using a similar hardware configuration as your HP autosampler as described in my June 1997 Analytical Chemistry article on trace analysis using headspace. The PE autosampler does a better job of minimizing carryover than the others on the market (at least in 1997). All the units of different manufacturers I have seen can perform good work if operated correctly.

I suggest you use blanks to clean your system after a sample likely to introduce carryover is injected.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By andrzejmurdza on Monday, August 23, 2004 - 11:35 pm:

jchromatographer1
thanks for your suggestion
you have right there are details of HS condition:
oven 80 dg C
loop 110 dg C
transfer line 110 dg C
carrier preassure 22 psi
vial pressure 15 psi
I want to check residual solvent in doxazosin mesylate but this substance is insolubility in water I can use DMF.DMSO is carryover my equipment and in the next run (only water) i obtain peak of DMSO and I steel have this peak even I run ten sample certainly.other peaks (aceton metanol toluen..) are absent.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Chromatographer1 on Tuesday, August 24, 2004 - 08:26 am:

Rotor material and transfer line deposits will absorb and adsorb DMSO and DMF. Steel contributes to this problem. You should have deactivated (glass or fused silica lined) tubing and sample loop.

You can increase the purge flow between injections to minimize the carryover, but if there are deposits, the water from the next injection will free the DMSO from the deposits and you will see a peak in your injection.

Replace all your tubing with fresh deactivated tubing and don't forget to clean your needle assembly. If you can have this deactivated for your HP as I did for my Tecmar(Genesis) 7000 you will see a reduction in carryover.

To minimize carryover my former company purchased a HS-40 which outperformed the competition at that time (1997).

Good luck !


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