Chromatography Forum

Dear All,

Can someone give me some suggestion on how to make clearly separation of MEK, IPA, metanol and denatured ethyl alcohol in a sample?? Thanks

Regards
Pang

Hi

A 624 type column should do the trick, the vendors usually have chromatograms with run condition on their homepage for "residual solvents".

Dear Krickos,

Thanks for your information. I not sure for the 624 type column. The column that I using now is HP-INNOWAX with 30m, 0.25mm (id), 0.25um (film).

Now the main problem that I facing is their retention time are very close, the actually four components in sample only present two peaks in the chromatogram. I not sure how the test condition for this case, because I just new to the GC. The oven temperature, the flow rate, how will it affect the elution rate of this sample? Thanks

Regards
Pang

Be sure your flow rate is close to optimum flow. While typical optimum flow for a capillary column is about 23 cm/sec rates up to about 65 cm/sec work well. Outside fo that range separation degrades.

If the column temperture is too warm, the compounds elute too quickly from a column - and elute together. If too cool, the compounds take too long to elute and the peaks become sufficiently broad that they are difficult to integrate or even detect.

If you are new to chromatography, you can save yourslef a lot of difficulty by folowing the advice Krickos gave above - find conditions established by someone else and use them. Even with about 30 years doing gas chromatograpy, I look to see what vendors suggest if I need to set up a sepration that I have not run before. A new column can be less expensive than supplies requried to develop a method on a column that will not work well for a separation.

Pang,

You have a 0.25 X 0.25 column. This is not a column that likes high loadings so my next question is, how much are you shooting?? In addition, you are shooting volatile components so even a Wax in a thin film will have a hard time separating these.

Best regards.

Agilent and Varian (now Vagilent ) had a column named Oxyplot which is able to do that separation. It could be even able to barely separate npropanol and ipropanol

Dear Don, AICMM, Aamorin,

Thanks for your advice. For AICMM, the injection volume is 1uL with split ration 50:1. The method that I using now is isothermal analysis with 30oC, with flow rate 0.5mL/min.

The GC model I using is Agilent 7820A.
Column 30m,0.25mm(id), 0.25um (film).
FID detector.

What other test condition can you all suggest to me since I have already running out of time for this project. Thank you very much.

Regards
Pang

Pang,

If you have a methyl silicone column you may be able to separate all four analytes. You may have tailing problems with the alcohols. A 5% phenyl column might be attempted.

Doing an analysis with the wrong column is difficult.

Good luck,

Rodney George

Dear Krickos,

Thanks for your information. I not sure for the 624 type column. The column that I using now is HP-INNOWAX with 30m, 0.25mm (id), 0.25um (film).

Now the main problem that I facing is their retention time are very close, the actually four components in sample only present two peaks in the chromatogram. I not sure how the test condition for this case, because I just new to the GC. The oven temperature, the flow rate, how will it affect the elution rate of this sample? Thanks

Regards
Pang

Well the WAX phase is inadequate even with optimum conditions MEK and methanol will more or less coelute in my experiance, also there is not much margin between IPA and ethanol either on that phase.

The 624 column or a type -5 column as rodney mention should work . Either of those, start with an isotermal temperature of 35-40°C for 5-6min then raise 10°C/min. That should give you a starting point. Gas flow, try starting close to the optimum flow for your gas (like ~30m/s for He).

I agree with chromatographer 1, the 95/5 (30 meters should be alright) column he suggested will work. I perform the analysis of highly volatile substances almost daily and those substances you mentioned seperate very clearly.
Maybe I have a small advantage with my thermodesorption unit as an injector (cooled with liquid nitrogen) but it should work without as well. Most important thing in my opinion is to keep the column temperature at a low level in the oven programme in order to avoid co-elutions.

0.5 mL/min seems a bit low for a 0.25 mm id column. I would not use less than 0.7 mL/min with helium carrier gas. (Hydrogen would be about twice as fast.)