Chromatography Forum

Hi,

I'm new to the cromatography analisis, so excuse me if my questions are too simple

I'm working at a pet radiopharmaceutical lab. We would like to perform the quality control to a new radiopharmaceutical and we use gas chromatography to quantify the residual solvents of the method. Since we produce radiopharmaceuticals we do the calibration tests with water samples, although the final radiopharmaceutical product would be in saline solution diluted with water.

The problem is that we can't get good repeatability with one solvent, dimethylaminoethanol. The same sample injected gives us from 200 ppm to 14 ppm. Anyway, we notice that there is great variability with small concentrations, like 25, 50 ppm (I know that our concentrations are big enough)

I read that there's some backflash problems with water samples, so I would thank any help if you can detect any flaw in our method:

GC: Varian 3900 with FID detector
Column: FactorFour VF-624ms, 30m x 0.32mm ID DF=1.80
Injector - 200ºC (split 1:5), injection volume 1ul
Oven:
- 40°C, 0-6 mins
- 40-200°C, 6-22 mins (10°C/min)
- 200°C, 22-23 mins
FID: 200°C, He 25 ml/min, H2 30 ml/min, air 350 ml/min.

Thanks in advance, and excuse my english mistakes!

One microliter of water can expand into a volume larger than your injection liner can hold. It depends upon what liner you are using.

Try injecting one half or one third the amount of sample and see if your results improve.

best wishes,

Rod