Chromatography Forum

Hello

I have some questions about my method for testing acetonitrile in an aqueous sample. I use a GC-FID

First my GC settings (GC 6890N):
inlet temperature: 200 °C
Detector temperature: 250 °C
Splitless injection: 1 microliter was injected with autosampler

Temperature program:
0-3 min: 60°C
after that it rise with 80°C/min to 220 °C then it holds that temperature for 2min.

Hydrogen and nitrogen: 40 mL/min
Air: 400 mL/min

Column: HP FFAP 30 m * 320 μm * 0.25 μm


1) I don't get consistent results. I've read that it's hard to get good results with a GC-FID for testing acetonitrile. But it's not impossible I hope? Because I don't really have an alternative. I found another method with GC-NPD but the upper range of this method is 5 mg/L and my range of concentration lies between 5 mg/L and 250 mg/L so that's also not an option.

2) maybe my column is broken. On the picture you see that at the end there're a lot of peaks and the baseline gets higher. I searched this and maybe this is columnbleed? Can I fix this or will the results be better with a new column?



Thanks in advance

Here's a link to the picture I'm talking about.

https://imgur.com/a/UINKxvP

It may be the FFAP column. Reading about it, the stationary phase contains acid, and acetonitrile can be broken down by acid. Maybe you need a column such as a normal Wax column or even one of the 624 phase columns https://www.agilent.com/en/product/gc-c ... cb-columns

The other option is to use either Headspace sampling or Purge and Trap, since acetonitrile is volatile enough to use those methods.

USP assay for ethanol uses ACN as the internal standard (instead of the more-commonly utilized n-propyl alcohol) and FC-FID, so my supervisor wanted us to do and validate our procedure using ACN. We used water as solvent, and didn't have any reproducibility issues.

No - we did not use FFAP.

USP assay for ethanol uses ACN as the internal standard (instead of the more-commonly utilized n-propyl alcohol) and FC-FID, so my supervisor wanted us to do and validate our procedure using ACN. We used water as solvent, and didn't have any reproducibility issues.

No - we did not use FFAP.

Which column did you use then?

It may be the FFAP column. Reading about it, the stationary phase contains acid, and acetonitrile can be broken down by acid. Maybe you need a column such as a normal Wax column or even one of the 624 phase columns https://www.agilent.com/en/product/gc-c ... cb-columns

The other option is to use either Headspace sampling or Purge and Trap, since acetonitrile is volatile enough to use those methods.

Thanks for the answer. The column that I use is made for analyzing organics acids. But if I inject acetic acid (400 ppm) in a water sample than I don't get any peak. Only the peaks at the end like I always have. So that's not normal I guess?