Chromatography Forum

Hi all,
since a couple of weeks, I'm trying to evaluate, and later validate, a proper method to determine ethylene glycol and ethylene chlorohydrin in water (as products from EO-sterilization). ECH is no prob considering linearity and precision, but EG fails desperately. EG shows acceptable linearity, but very bad precision. Additionally, I find EG in the blanks following the measurement (syringe or back flash problem due to the high injection volume?). I found the following components and conditions, when I started this job:

Column DB-Wax 30m x 0,25 µm from J&W
glass liner with glass wool
Injection volume 3 µl, Split 20:1
Injector: 250 °C
Detector: 320 °C

I'm pretty new to aqueous samples in GC, so I would appreciate some hints and suggestions to optimize this method (even if another column is more appropriate).

thx a lot and have a nice weekend
Bernie

I would expect that you are correct in noting the flashback of the large injection sample of water is the reason for your problems.

If you can inject slowly manually, or have an autosampler that has an adjustable injection rate, inject your sample at a rate of 0.25µL per sec or even slower and then run 'burst' injected blanks after each trial to see if you have carryover from the backflash.

If you can inject slowly you have a chance to make this analysis work. Try to minimize your injection port temperature as a higher temperature will cause more backflash.

You can of course increase your split ratio but this is counter productive to your goal.

If your initial column temperature is low you will refocus your analyte plug and get good chromatography as you program your oven.

You might want a plug of methanol or clean water with an air gap behind your sample in your syringe.

Just remember, if it were easy anybody could do it. Good luck.