Ethylene glycol in water samples

[doomtrain]

Hi
I'm doing my bachelor's thesis and i am supposed to develop a GC-method for analyzing mono-, di- and triethylene glycol in water samples within 1-100ppm.

i'm using an MMI GC-FID with a HP-5 column. i have tried Stabilwax with poor results. i have also tried 2 different types of liners (2mm dimpled liner and one with glass wool). i'm currently injecting 25ul to be able to get peaks on 1ppm.

My problem is that the liner with glass wool gives a large carry-over due to flashback, and the dimpled liner doesn't give any results on lower concentrations but large deformed peaks on 100ppm.
i have tried lower injection volumes to get rid of the flashback, but then i loose a lot of sensitivity. anybody with experience with MMI who can help me?

the company i'm doing it for doesn't want any sample preparations if it can be avoided, just take the water sample and inject it as it is.

Any pointers will be much appreciated

/Emil

[chromatographer1]

25 microliters of water !

Flashback, you say? Really (pardon the attitude, but REALLY!)

I am sure even the HP-5 column won't last too long under those conditions.

Now is the water pure with only the glycols present? If not, then reproducibility and feasibility is only a dream. How happy will the company be when if fails in the field after a few days?

Can you do SLOW injections manually, or can you use a sampling valve?

I would avoid capillary columns and use a micropacked porous polymer R column 100/120 mesh or 80/100 mesh, 20 to 40 inches in length, glass wool inserted on the inlet end 3-5 inches from inlet (vaporization space) Tube should be FS coated SS, 1 or 1.25mm ID. Use 20cc/min carrier flow.

BY the way, I would use LC with a TC detector to do your analysis far more easily and quickly.

35C RP-C18 15cm 10micron packing. 100% water mobile phase.

best wishes,

Rod

[doomtrain]

Guess i should have mentioned that i'm using an MMI and programmed temperature vaporizer with slow injection so it is adapted for large volume injections, so no offense taken. i started out with a "standard" method they had tried. i tested smaller sample injections without results.

The samples wont be clean, it is industrial sewage. And there was talk about wanting to run salt water samples as well, which i'm not to glad about.

The only instrument i have access to is a GC-FID, so i hope there is a way to resolve these problems

Regards Emil

[chromatographer1]

I am afraid MMI means something different to me than what you have. My apologies.

How often do you have to clean your injector? Every sample?

Good luck in your research. Better thee than me.

Rod

[DSP007]

If " my memory serves me" PND-F (russian national formular "protection of natural objects") 14.1:2.250-08 for analysis of wastewater ( ethylenglicol & DEG) recommends : packed column wich polisorb ( analog Chromosorb 103) , temperature 230 C or packed column with 5% Carbowax on Dinohrome (analog Interon) at 170 C.

[doomtrain]

okey, thank you, i'll try that if i can't get any results soon.

Best regards Emil

[chromatographer1]

Carbowax 20M on Chromosorb 101 porous polymer beads has also been used for EG in a packed column application.

good luck,

Rod

[AICMM]

doomtrain,

Very tough (in my opinion) without sample prep at those levels. One of the first things I would look at is how little you can inject to get to something like 10 ppm since your peak shape will (hopefully) improve as you go to lower injection volumes. The fundamental problem is the expansion volume of the water ... Another suggestion would be to try a 1:2 dilution with some other flash amenable solvent like IPA.

I would have suggested an alternative detector (in particular an argon ionization detector) for improved sensitivity but you are limited to FID.

Finally, even though they don't want to, I would look at an extraction pretty seriously in an attempt to get to those levels by FID.

Best regards,

AICMM

[AICMM]

doomtrain,

One more comment, is SPME an option?

Best regards,

AICMM

[doomtrain]

Thank you for all the help. I'm going to have a meeting with my supervisor today, and i'll try to see if i can convince them to take these options into consideration.

Best regards Emil