Method development for carboxylic acid analysis using DBFFAP

[kathironfly]

I had Agilent 7890A GC with FID.
My interest is to detect the carboxylic acids (in micromoles) like succinic acid,malic acid,pyruvic acid,2-oxo glutaric acid,citric acid,oxaloacetic and acetic acid.

I'm trying to develop a method for analysis of above carboxylic acids in DB-FFAP (30mx0.25mm,0.250um) and detect in GC-FID in underivatised form.

Initial method settings to find retention time of carboxylic acids are mentioned below:

Heater temp: 220C
Carrier gas: Nitrogen (1ml/min)
FID Detector temp: 250C,Hydrogen gas:30ml/min,Air:400ml/min,50Hz data sampling rate
Oven program: Initial 80C for 1min;150C for 2min at rate of 10C/min;then to final 220C for 5min at rate of 10C/min
Injection mode: Splitless, injection volume:1ul, standard preparation in filtered MilliQ water.

Now the issue is couldnt able to detect the individual retention time for all carboxylic acids. If we inject a pure standard( Sigma GC grade,) of individual carboxylic acid(50mM), high conc to detect the desired peak but end up in many peaks.

If i do post run with blank (just carrier gas) after each injection of standards, there will be no peak detection in post run.

Can anyone suggest me to alter the method or is it only possible with derivatisation in FFAP column for carboxylic acids ???

I could appreciate reply.

[Peter Apps]

With the exception of the acetic acid these are not compounds that GC is suitable for, unless they are derivatized.

Peter

[chromatographer1]

Difficult to do as free acids,extremely difficult.

Beware of enol forms being derivatized if silylation derivitization is used.

Beware of anhydride formation if esterification by acid catalyst is used.

This is why HPLC and IC were invented.

Be smart, don't be stubborn.

best wishes,

Rod

[magda roth]

Any suggestions of derivatizations? I have HPLC/UV. To analyze it as free carboxylic acid at 210nm, I have too many interferences. Would prefer to derivatize and run at higher wavelenght. As an added bonus: this is a plant operations, cannot do a lenghty procedure. Who said analytical chemists are bored?