Iím looking for advice on doing injections of a mixture containing low boiling solutes in water. I'm currently analyzing a four-component sample (In order of elution = Ethylene Oxide, Acetonitrile, Ethylene Chlorohydrin, and Ethylene Glycol) in water. In particular Iím having problems with peak tailing and poor reproducibility of my early eluting peaks, especially Ethylene Oxide. The later peaks such as Ethylene Chlorohydrin are consistently sharp and reproducible. I also always get an unidentified peak at a retention time that matches the dead time.
My current setup is as follows:
Column: Polar Wax Column (30M x 0.53mmID x 1um)
Guard Column: 5M Uncoated Fused Silica
Initial Oven Temperature: 40C or 60C
Oven Ramp: 12C/min
Final Temp: 220C
Injection Temps: 150C or 250C
Carrier Pressure: 5psi
Carrier Flow: 5mL/min
Split Flow: 20mL/min
Split Ratio: 4 to 1
Injection Volume: 1uL
Injection Liner: Deactivated glass liner packed with deactivated glass wool
Detector: FID, 300C
I know that water expands a great deal upon injection so I want to try to minimize backflash while still maintaining the ability to detect down to 1ppm. The above scenario provides me with sufficient response for 1ppm but itís not reproducible.
Areas that Iíve thought to explore and am looking for feedback on include:
1.Column: Different phase? Longer column? Smaller ID?
2.Guard Column: Eliminate? Try a polar deactivated one to for better water wettability?
3.Injector Pressure: Higher pressure through pressure pulse injection?
4.Injector Liner: Try a laminar cup splitter? Other kind of liner?
Iím hoping someone has experience or knowledge on this specific type of analysis involving such a low boiling component in a water matrix. Any suggestions would be very much appreciated. Please respond to this list or email me directly.
By Ralph on Thursday, May 8, 2003 - 04:17 am:
From your supplied conditions I would be concerned with the starting oven temp. The water is going to condense and cause all sorts of problems. Oven temps at or above the boiling point of water give better results. This may cause you to lose resolution of your lower boilers but try it anyway, hold at a 100 for several minutes. Consider an extraction technique such as SPME.
The dead volume peak may be an artifact of the water injection or an impurity. Try increasing the hydrogen flow to the flame to make it more stable - you will lose some sensitivity. Does it also occur with repeated water injections only?
I still use a packed column for ethylene oxide 0.8% THEED on Carbopack C (Supelco) but this is used to resolve it from acetaldehyde which co-elutes on most phases.