Chromatography Forum

Rganga,

What phase are you using?

I did a calculation using Agilent's flow calculator. With those dimensions and at 170 C the calculator gave a flow rate of about 0.2 mL/min. This is way too low for a 0.32 column. Try something on the order of 75 or 80 kPa as a starting point.

Best regards.

Hi AICMM

I suspect that pa (not even kpa) is being mixed up with psi. Depending on what GC he has it is easy to do - my Varian 450 run from Galaxie can have one set of units on the front panel and another on the screen.

Peter

At what Retention time is an unretained peak like methane, or at least, the front of your solvent peak?

It should be about 2-2.5 minutes, or slightly longer, depending upon your solvent.

Rod

hello.
i have the same problem. i do fatty acid methyl esters analysis with my gc fid Hp5890. the solvent is n hexane and when i inject the standard i cant see the C4,C6,C8 and C10 fatty acids, because the solvents peak are too broad. what should i do? did you solve your problem Rganga?

hello.
i have the same problem. i do fatty acid methyl esters analysis with my gc fid Hp5890. the solvent is n hexane and when i inject the standard i cant see the C4,C6,C8 and C10 fatty acids, because the solvents peak are too broad. what should i do? did you solve your problem Rganga?

I worked with fatty acid methyl esters for 4 decades, but in my business we were primarily interested in C8 to C18. We used packed cyanopropylsilicone column for these for most of those years, then switched to capillary columns of similar phase. For sure on packed columns we couldn't see C4 or C6, and we used a completely different procedure for a couple of years when C6 amount was of interest.

I never tried C4 and C6 fatty acid methyl esters on the capillary column, but also remember that those low fatty acid methyl esters might not fully extract into n-hexane.

hello
thanks for your answer. but i work for Institute of Standards and Industrial Research of Iran. i should analysis and determine percent of fatty acids methyl esters in food stuffs like butter. they have limitation. for example percent of C4 in butter should be 1-5 percent. so when i can't see peaks for C4,C6,C8 and C10 the percent of other fatty acid methyl esters whuld be wrong. isn't it?

hello
thanks for your answer. but i work for Institute of Standards and Industrial Research of Iran. i should analysis and determine percent of fatty acids methyl esters in food stuffs like butter. they have limitation. for example percent of C4 in butter should be 1-5 percent. so when i can't see peaks for C4,C6,C8 and C10 the percent of other fatty acid methyl esters whuld be wrong. isn't it?

You should change your method/column to achieve good separation of C4 and the rest from solvent peak.

hello
thanks for your answer. but i work for Institute of Standards and Industrial Research of Iran. i should analysis and determine percent of fatty acids methyl esters in food stuffs like butter. they have limitation. for example percent of C4 in butter should be 1-5 percent. so when i can't see peaks for C4,C6,C8 and C10 the percent of other fatty acid methyl esters whuld be wrong. isn't it?

https://www.restek.com/chromatogram/view/GC_FF00651

Looking at this example from Restek, they use Dichloromethane as the solvent when looking for C4 fatty acid methyl ester. I think hexane is going to co-elute on most columns and the response on the FID is so high that even a tiny amount tailing out will cover up the analytes of interest. Dichloromethane or Chloroform would not respond to the FID as well and give much less interference.

Another trick to sharpen the solvent peak is to use a guard column that is the same polarity as the solvent, especially if the solvent does not match the polarity of the analytical column stationary phase. When I inject Ethyl Acetate onto a 5 phase column I use an intermediately polar deactivated guard column to reduce the peak tailing of the solvent, if injecting Dichloromethane I use a non-polar guard column if the column is a polar wax column for the same reason.