Method for Ethanol analysis by agilent GC 7890A and HP-5

[umu]

Dear all:

I am trying to analyze Ethanol by GC 7890A, HP-5 column, and FID detector. I am doing manual injection and using isopropyl alcohol as an internal standard. The problem I have is the ethanol peak and the isopropyl peak come out very close at a retention time successively 2.9 min and 3.1 min. How can I increase this separation to have the isopropyl peak to come out little bit later than 3.1 min? I'm using now is:
Injection: 250 oC, 1 ul,
Oven programing: intial 40 oC hold for 1.7 min, ramp 10 oC/min, final 250 oC hold for 2.67 min,
FID: 300 oC.

Any suggestion? Thanks.

[chromatographer1]

Change isopropanol to n-propanol or butanol.

Don't make choices that make life difficult for you.

If you want difficulty, try using acetaldehyde instead of isopropanol. I have other even more difficult choices if you want to hear them.

You can always inject less than 1 microliter, too, if you wish to make things easier.

Any questions?

Rod

[chromatographer1]

There are much better choices of column as well, but I assume from your post you want to stay with the column you have.

best wishes,

Rod

[michaelbarnes42]

If you don't want to change your internal standard, I am currently using a DB-624 column, and I have retention times of 5.1 for MeOH, 6.8 for EtOH, and 8.0 for IPA.

[michaelbarnes42]

Also, I use a different temp program, I hold it at 40 C for 7 minutes. Then ramp at 30 C per minute to a temp of 250 C.

Maybe, keeping your oven temp low for longer will help improve your seperation.

[umu]

Change isopropanol to n-propanol or butanol.

Don't make choices that make life difficult for you.

If you want difficulty, try using acetaldehyde instead of isopropanol. I have other even more difficult choices if you want to hear them.

You can always inject less than 1 microliter, too, if you wish to make things easier.

Any questions?

Rod

It's works with n-Propanol. Thank you for your time.

[umu]

If you don't want to change your internal standard, I am currently using a DB-624 column, and I have retention times of 5.1 for MeOH, 6.8 for EtOH, and 8.0 for IPA.

Ok, thank you for your time I will consider the column.

[umu]

Also, I use a different temp program, I hold it at 40 C for 7 minutes. Then ramp at 30 C per minute to a temp of 250 C.

Maybe, keeping your oven temp low for longer will help improve your seperation.

Ok, I will try that. Thank you for your time.

[chromatographer1]

I am glad you found an answer.

FYI

This topic has been repeated over and over and can be searched in the older posts on the forum. Always review older posts before posting a question. It can save you valuable time and effort. Also a quick review of column vendor's web sites can supply you with options you might never consider, and it is all for free.

best wishes,

Rod