determination of ppm ethanol & ppm aceton in aqueous buf

[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!

[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

[larkl]

I believe that Poraplot Q is sensitive to water and your samples will not run well.

[dpr]

Poraplot Q will be problematic with Aq samples.

A Thames Restek RTX-1 will do it.

A 30m column will give good seperation.

[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.

[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.

[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.

[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?)

[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

[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