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determination of ppm ethanol & ppm aceton in aqueous buf
Posted: Tue Oct 06, 2009 4:52 pm
by Tracer
Hello
I want to develop a method to detect and quantify ppm levels of ethanol (and aceton as a standard) in aqueous buffers
The system that we use is: Poraplot Q (5m), trace-GC and injection-needle 10µl (it's the smallest size possible)... the maximum split is 250
It's my first time doin' GC, so some suggestions (temperature and flow programme) would be very helpfull
Thanks!
Posted: Wed Oct 07, 2009 12:34 am
by chromatographer1
Tracer,
This sounds like a student project. Perhaps you should have posted this in that section of the forum.
An isothermal oven should be adequate for the separation of ethanol and acetone, anywhere between 60°C and 200°C should work.
This issue is getting enough sample onto the column to detect 1 ppm.
A solid-phase microextraction fiber needle to sample your buffers should work fine for your needs.
Good luck on your homework.
best wishes,
Rodney George
consultant
Posted: Mon Oct 12, 2009 12:19 pm
by larkl
I believe that Poraplot Q is sensitive to water and your samples will not run well.
Posted: Fri Oct 16, 2009 2:01 pm
by dpr
Poraplot Q will be problematic with Aq samples.
A Thames Restek RTX-1 will do it.
A 30m column will give good seperation.
Posted: Mon Oct 19, 2009 3:37 pm
by CE Instruments
Headspace
No sampler ? You mention trace-gc ? Thermofisher ?? If so get one of the special water injection liners 453-003-20, inject 1ul from your 10ul syringe with a low split ratio.
Posted: Sat Oct 31, 2009 4:03 pm
by TimGG
Oh well, I'm using PLOT Q for Water, IPA and Ethanol, so I think your system would be fine.
here's how I set it up
Injector 200C, 10:1 Spilt
Oven: 170 for 5 mins
Detector: 250C, Hydrogen 60, Air 300, Make up He 3
Hope it helps.
Posted: Sun Nov 01, 2009 1:21 am
by thohry
I analyzed traced water in an organic solvent and with Plot Q. I am not sure the reverse could work: trace ethanol in water.
Posted: Fri Nov 20, 2009 10:40 am
by Tracer
Thanks for your comments.
We are now working with phosphate buffer with ethanol (100mM-0mM) and aceton as standard (10mM). 150°C-250°C at 20°C/min. Works fine, however, we have a peculiar problem:
When we set up a calibration curve (Area ethanol/Area aceton) as a function of the concentration ethanol, we obtain a rico x
When we then increase the pH of our buffer system (phosphate pH 6.5) to pH 10-11, we obtain a rico 1.5x (linearity remains perfect)
So what can be the explanation?
(Does the increased pH (injection volume only 1.2µl) damage the GC-column?)
Posted: Sat Nov 21, 2009 12:18 am
by chromatographer1
If I understand your post correctly, you adjusted the pH of your phosphate buffer to a basic pH.
What kind of phosphate buffer are you using? sodium?
What ion are you adding to change the pH ?
What is the meaning of your abbreviation of RICO ?
Rodney George
Posted: Sun Nov 22, 2009 11:58 am
by Tracer
If I understand your post correctly, you adjusted the pH of your phosphate buffer to a basic pH.
What kind of phosphate buffer are you using? sodium?
What ion are you adding to change the pH ?
What is the meaning of your abbreviation of RICO ?
Rodney George
sodium indeed... the pH was increased by adding some µls concentrated
NaOH (10M) to the buffer... (alkalinization is needed to stop a reaction which would otherwise continue in the vial during analysis)
with rico i mean
slope of the curve... sorry for the terminology
best regards