Naphthenic acid analysis

[Ricardo]

Does anyone know if naphthenic acid can be analyzed by GC? It seems to be a hot topic in research these days but I can't find any information on the internet or on this website. I am trying 140 ppm in water today and have reproducible retention times but the area counts are rising. I then injected water and the area counts are now decreasing.

Injector is 150, split is 16 ml/min
FID Detector is 200
Oven is 60 to 150 at 30C/min, hold for 5 min.
Column is a PTE-5 from Supelco, 30 m x 0.25 mm w/0.25um phase thickness
non-polar 5% phenyl/95% Polydimethylsiloxane

The standard I am using is trans-4-Methyl-1-cyclohexanecarboxylic acid.

Any help would be greatly appreciated!

[Schmitty]

Suggestions:

Temps might be too low for this compound (bp of 135°C at 15mmHg).

Water is a poor injection solvent for GC.

What type of injection port liner are you using/trying?

[Ricardo]

I am using an Agilent split liner with cup and glass wool/column packing, 4 mm I.D.
I baked out the column and raised the injector/detector temperatures and did get a couple of peaks out at the end. It appears to be sticking on the liner and gradually bleeding off causing inconsistent area counts. I am now trying hotter injector/detector temperatures.

[KC]

Must you shoot water? I guess you can do it because you are but I have never shot water on a GC.

[Consumer Products Guy]

If you inject water solutions, keep the injection volume to 0.5 ul; water expands a ton when it vaporizes, will overflow the liner volume otherwise.