Two question about GC

Chromatography Forum: GC Archives: Two question about GC
Top of pagePrevious messageNext messageBottom of pageLink to this message  By Anonymous on Sunday, September 7, 2003 - 08:24 pm:

Dear members,
1.Did anyone analyze the components of sebum by GC-FID? Any experiences in analysis and sampling?
2.An expert told me: low-bleeding columns(GC) are being selected out from a batch of ordinary columns but there is no special tech in manufactoring. Is this idea right?
Michelle


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Jason Ellis on Monday, September 8, 2003 - 10:35 am:

I can't comment on the sebum analysis, as I don't have any material at hand that discusses that particular application.

I can comment on the low-bleed GC column question, though. There are different ways that manufacturers can produce low-bleed GC columns. Some manufacturers "hand select" columns from the normal population and sell these as low bleed. Other manufacturers derive the low bleed by different manufacturing means (phase or deactivation chemistry, processing techniques, etc.). For example, phenyl-containing polymers can be "reinforced" by the addition of arylene groups in the polymer backbone. This produces phases similar in selectivity to non-aryl counterparts but these phases bleed less and are more thermally stable (higher upper temp limits). There are other chemical means of producing low bleed polymers as well.

If you are wondering about a particular column you are using or are interested in using, then I recommend contacting the manufacturer and asking them how the low-bleed is derived (thru manufacturing or hand selection). This can be valuable information for later if you are doing method development (ie. in finding equivalent columns).

Best regards,
Jason Ellis
GC Column Support
Agilent Technologies


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Anonymous on Friday, September 12, 2003 - 12:40 am:

Hello, Jason,
I used a column from J&W, DB-17ht to do this analysis. Now I am not sure whether it is safe to use this column at 365c (highest use temp) since only at 320c the singal of baseline increased about 25PA comparing at 100c. Did this change resulte from phase loss?
Thanks for your last explanation.
michelle


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Jason Ellis on Monday, September 15, 2003 - 08:22 am:

The DB-17ht has a maximum temp limit of 340/365C. This means you can take the column to 340C and hold it for "a long time" without causing any significant damage. 365C is the temperature program limit -- we say that you can take it up to that temp if you need to for your method, however you should only hold the column at that temp for maybe 5-10 minutes maximum at a time. At the higher temperature you are stressing the polymer more so it does reduce column lifetime somewhat. You will have to balance that possible lifetime reduction with the potential benefits of using the higher final temp for your method (shorter analysis times, better possible resolution for high boilers, etc).

Running any column at temperatures above 340C is going to be difficult, especially a mid-polarity phase like DB-17 (50% phenyl). Extra bleed will be evident at those very high temperatures -- remember that the "ht" column you have is not a low-bleed phase, but rather a column with phase coated in special "high temperature" fused silica tubing. This "high temp" fused silica has a different polyimide coating on the outside that can withstand tempertures up to 400C, however the upper temp limit of the column is also determined by the stability of the phase (hence the 340/365C of your column).

After considering the method, I don't see any reason why this method can't be done on a DB-1ht or DB-17ht phase (or equivalent). A column with a high upper temperature limit will be necessary to elute all the components of the mixture. Ultimately the phase selection will depend upon the resolution required of the components in the mixture. If possible, the lower polarity "1ht" might be a better match (higher upper temp limit and lower bleed at those temps due to greater phase stability).

If you'd like to discuss this in more detail, please feel free to contact me directly.

Regards,
Jason Ellis
Agilent Technologies


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Anonymous on Sunday, September 21, 2003 - 10:29 pm:

Janson,
Many thanks.
I am from China.So could I know your email address?
Michelle


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Anonymous on Sunday, September 21, 2003 - 10:30 pm:

Jason,
Many thanks.
I am from China.So could I know your email address?
Michelle


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Anonymous on Monday, September 22, 2003 - 06:33 am:

click on his name in blue in the posting and you may email him.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Anonymous on Monday, September 22, 2003 - 06:44 pm:

Thank you.


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