GC sensitivity

Chromatography Forum: GC Archives: GC sensitivity
Top of pagePrevious messageNext messageBottom of pageLink to this message  By Anonymous on Friday, September 19, 2003 - 11:01 pm:

Hi,

Recently, i bought a GC and i am still an amateur. I read a lot of books about GC and i have a question. Do type of carrier gases used affect GC sensitivity e.g. the GC sensitivity is significantly better if we use Hydrogen gas compare to Helium gas as the carrier gas?? Please guide me if i am wrong. Thank you very much in advance. I would be glad if anyone can shed some light on this matter.

Regards,
steven


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Anonymous on Saturday, September 20, 2003 - 12:08 am:

which type of detector if you are using


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Anonymous on Tuesday, September 30, 2003 - 06:37 am:

It depends on the analysis You make. Detector incl. Give us more input.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Anonymous on Wednesday, October 1, 2003 - 05:11 am:

Capillary or packed columns?

Generally the carrier does not make a difference in detector sensitivity.

For some detectors some gases are not possible to be used.

For the universal flame ionization detector, the present designs give better sensitivity with nitrogen as the column makeup gas, that is if you need a makeup gas, packed column don't need it.

PID, ECD, TCD generally work longer and better with Helium carrier, GENERALLY.

pHID detectors require a high purity of Helium and won't work well with Hydrogen or Nitrogen.

TCDs may have a hot wire or a coated thermister and depending upon the analyte work better with nitrogen or helium.

Books could be written and have been. Read them.

Good luck.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Anonymous on Thursday, October 2, 2003 - 06:34 am:

You can run hydrogen at a higher linear velocity than nitrogen or helium. Go on-line and search for "van Deemter plot", I am sure you will find one. What a van Deemter plot shows is the height equivalent for theoretical plate vs linear velocity.What you will see is that the optimum linear velocity range for hydrogen is much wider and flatter than nitrogen or helium, you can run hydrogen up around 50cm/sec while you can only run helium around 30cm/sec, so you have faster chromatography. Maybe this is what you heard when you thought H2 gave better sensitivity.

PS. I once had a fire in my GC oven running hydrogen as carrier, no damage done, but it was pretty scary.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Leon on Thursday, October 2, 2003 - 11:25 am:

"GC sensitivity" might mean many things. I assume that the question is about the effect of a carrier gas on the ability of a GC system to detect and measure the lowest possible amount (or concentration) of the same component in the same sample. If that is the case, keep reading.

First, although it is conceivable that carrier gas type might directly affect sensitivity of a detector in a significant way, I am not aware of such type of a detector.

Second, each carrier gas type has its own optimal speed of analysis. This can indirectly affect the sensitivity of the same GC system. For example. Replacing helium with hydrogen can improve the sensitivity by 10 to 20% (more accurate prediction is possible with more details about the system). Replacing nitrogen with hydrogen can cause up to a factor of two improvement.

Where is the bottom line? In most cases, the level of expected improvement in sensitivity can not justify switch from one carrier gas to another. The best course of action might be just to forget it because it is not worth it. (Otherwise, let me know. With more details regarding a column and a GC system, it is possible to suggest what exactly should be done to realize a possible sensitivity gain, and how large (or small) would be the gain.)


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