Chromatography Forum

I am testing for three analytes: Acetaldehyde, Benzene and Limonene using Glyceryl Triacetate as solvent. Adequate separation between the analyte peaks are obtained, however the following problems are still encountered: rounded peaks for Acetaldehyde and Benzene as well as interfering peaks on the Acetaldehyde. Attemps to optimize the GC/FID (headspace injector, column: BPX5, 30m x 0.32mm x 0.25micron) parameters to remedy these problems were made but unsuccessfully. Any suggestions will be appreciated.

A bit more detail on what conditions you are trying to use might help. Temperatures, carrier gas, flow rate, etc.

Glyceryl triacetate is not my favorite solvent for GC because it is relatively high boiling - and high boiling solvents can lead to a reverse solvent effect - broadening of pleaks eluting before the solvent.

Don gave some solid and accurate advice.

What to do? You might try adding some water to the dissolution mixture and lower its temperature.

All three should partition easily, especially if some water is added. Are you overloading the column? Did you try using a smaller sample loop or a smaller sample?

Little information = poor advice (talking about me, not Don)

best wishes,

Rod

Thanks for the advice so far.

GC Parameters - Carrier (Nitrogen) flow: 1.0ml/min; Split Ratio: 10:1, Oven program: Initial: 30degC for 5min, ramp: 11degC/min , Final1: 140degC for 5min, ramp: 45deg/min, Final2: 300degC for 5min. Injector: 250degC, detector: 250degC.

HS Parameters - Carrier Pressure: 20.0psi, Needle Temp: 210degC, Transfer Line Temp: 210degC, Oven Temp: 200degC, Pressurize Time: 0.2min, Withdraw Time 0.2min Injection Volume: 0.20ml, Thermo Time: 30min, Injection Pressure: 20.0psi.

Your HS temperature is extremely high.

You should not require a temperature more than 80C , perhaps even lower. If you add water to the sample your recoveries of your analytes should increase greatly.

best wishes,

Rod

The final temperature for the column is also too high - it will shorten the column lifetime, and since it is 50C higher than the detector any crud that bleeds off the column will tend to deposit in the detector.

Peter

That temp was that high so you could get any GTAcetate off the column. The better plan would be to not get any on the column in the first place. Lowering the HS temperature accomplishes that. But if you believe it is a problem, then raise the detector temp to the final column temperature. Stay 20 degrees below the max temp of the column in any case.

best wishes,

Rod