Chromatography Forum

Hello,

I am quite new to use GC, therefore my knowledge here is pretty limited .
We use a method to quantify hexanol and acetic acid in ethanol. With this method we can detect concentrations of 2 ppm (µg/ml) for hexanol / of 13 ppm (µg/ml) for acetic acid or higher. Apperently the concentrations of our samples are lower than these values, since we don't see anything. Now we wonder if it is possible to enhance the method.

Our method is:

1. GC 6890 with FID
2. Column Innowax (polar)
3. Injection: 1 µl
4. Inlet: splitless @ 220°C, purge time 1 minute, Helium
5. Oven: 60°C up to 220°C mit 10 K/min

Any suggestion to do it better are higly appreciated.

Try large volume injection, you will need some packing in your inlet liner, deactivated glass wool is about as good as anything, look up Focus Liners.

The sharper the peaks the lower the LOD / LOQ, so use the highest carrier gas velocity you can work with. If you are not already using it, switch to hydrogen as carrier gas.

Peter

With this method we can detect concentrations of 2 ppm (µg/ml) for hexanol / of 13 ppm (µg/ml) for acetic acid or higher. Apperently the concentrations of our samples are lower than these values, since we don't see anything.

I just have to ask: since these levels are so low, why is it important to "know".

Tough to define "zero".

Try large volume injection, you will need some packing in your inlet liner, deactivated glass wool is about as good as anything, look up Focus Liners.

The sharper the peaks the lower the LOD / LOQ, so use the highest carrier gas velocity you can work with. If you are not already using it, switch to hydrogen as carrier gas.

Thank you for your replay. I will try that!

I just have to ask: since these levels are so low, why is it important to "know".

Tough to define "zero".

That is a good question. The samples were taken out of production trials, where different process settings were used. In order to have a correlation between settings and concetration of these chemicals you need signals. No signal is good, having signals is better, than you know which direction for the settings is better.