Column temperature Inicial with fermentation samples

[juaant]

Hello, I´ve been trying to analyze samples similar to fermentation process (lactic acid-water-ethanol and ethyl lactate "10:50:30:10" more or less in volume).

The problem is bad quantification of ethyl lactate when I analyzed with initial temperatura in column 70ºC but when I analyzed with 100ºC of temperature the method is more or less correct.

My question is Why is not possible injection with this temperature, I´ve analyzed PCBs in hexane with temperature 50ºC in column less of tb of the hexane (70ºC) and I hadn´t problem?

The method is chromatography gas with FID detector:
- Column Nukol 30 m x 0.25 mm x 0.25 of fused silica
- Detector and injection 200ºC
- Flow 1 ml/min
- 0.5 microlitres of sample for injection
- temperature ramp: initial of 70 or 100ºC the final always 200ºC

My separation is correct.
Thank you

[AICMM]

juaant,

Water does not behave like most solvents and columns usually don't wet all that well with it. Starting at 100C nominally (and I would guess only nominally) keeps the water in the gas phase and moving down the column rather than beading up on the stationary phase and soaking up the ethyl lactate. The puzzling thing to me is that the lactic acid appears to chromatograph well and not the ethyl, I would have expected both to look poor.

At 50 you are below the boiling point of hexane and it re-condenses (nicely) in the stationary phase in a process called solvent focusing.

Some things you might want to try; thicker film, hotter injection temp, even hotter initial temp to ensure water stays gas phase, split injection. Also, make sure your liner is big enough to contain the entire expanded volume of water on injection (see lots of other posts about this.)

Best regards.