Dear Anvita,

1. I hope you optimized the liner velocity of the carier gas (or flow rate).

2. Does the peaks are overloaded (much higher than other compounds) or not symmetrical?

If:

1 is no - check what is the optimal value for your column diameter and type of carrier gas

1 is yes, 2 is yes - try to dose lower volume and/or increase the split ration

1 is yes, 2 is no: try to use smaller rate in your temperature program or/and lower initial temperature.

regards,

G

What are you trying to do? Fatty acids in cotten seed oil are determined using the FAME (Fatty Acid Methyl Esters) procedure. They are derivatized (esterified) in order to increase their volatility and detectability.

In GC, the greatest impact on selectivity is the column stationary phase. Unlike LC, the mobile phase (He or H) is inert and can't be modified to affect elution order. You can play with the temperature program and flow rate, but usually that only makes minor changes in resolution, oftentimes at the expense of run time. Thus, if this was a problem I was facing, I'd look at a column with another stationary phase chemistry.

Bruce Sir, can you please elobrate a little on your answer. I am getting nice peaks for palmatic acid but my oleic acid peaks are merged with Linoleic acid peaks. How to seperate them?

Hey Anvita Sharma,

for this seperation you need a more polar stationary phase like a WAX column to seperate the n-C18-ene-acid from n-C18-diene-acid. Here I send you an application from Agilent.

Anvita see Manfred's answer. The FAME method has been well tested. The AOCS (American Oil Chemists Society) has a lipid library.

A good and popular alternative for WAX stationary phases are Ionic Liquid based stationary phases. You can look on Supelco website - there is a number of applications including your purpose. The advantage besides interesting selectivity is their thermal stability - comparing to wax.

You have given us exactly zero information. You don't specify sample preparation, injection conditions, column nor temperature program, yet you post here expecting us to be able to solve your (undefined) problem. This is not a site where magicians reside; most of us who post answers are actually serious scientists. You are at a university; surely there are resources available who actually understand basic chromatography. If there are not, then re-post your question with some thought and some indication that you have actually tried to resolve this issue.

Mark is totally right! That is why I posted a 0-1 set of "solutions" ;)

Anvita,

As others have indicated you do not supply enough information about your setup for us to give much guidance. You can try reducing your initial oven temperature and holding it for a short isothermal period of one or two minutes to see if the separation improves. If these peaks are large relative to the rest of your scan, you can try diluting your sample more, or increasing your split ratio if using a capillary GC. Otherwise you need to make sure you are using the correct column phase, phase thickness, column diameter, and column length. Your carrier gas type can also influence the separation significantly.

Anvita,

For GC-MS chromatograms you can try to make integration for "extracted" ion chromatograms - check different m/z values, probably you can find ions "specific" to only one of the compounds from this pair.

regards,

G

Like Mark Krause said, there is no way that anyone can sensibly tell you how to do things better unless you tell us what you are doing now.

Unfortunately ResearchGate has regular contributors who just guess what the problem might be instead of taking the trouble to find out, and post generic advice or links that might be irrelevant for all anyone knows.

Dear Anvita, Lot of valuable replies are given to you by many scientists. I totally agree with Bruce. Fatty acid composition in edible oils is studied by FAME (Fatty Acid Methyl Ester) method. You can use BF3-Methanol reagent for the esterification. The selection of column is very important. A polar column like a Wax column is recommended for the separation. You need to optimize the temperature conditions like starting temperature, ramp rate etc. Also avoid injecting a high concentration sample either by dilution or by increasing the split ratio.

I agree with everyone on this, but it you're looking for a quick fix to your current method - just use a slower temperature gradient and inject less sample (or dilute your sample). The combination will probably separate the two peaks you're concerned about.