Chromatography Forum

I am used HPLC a fair bit but know little about GCMS although i am currently charged with using one.

My issue is this. I want to measure ethyl lactate so i have to dilute it. The question is in what?? Are standard solvents such as ethanol, methanol, hexane generally used??

Now if i use one of these solvents to dilute, how come they dont saturate the detector?

The final question is that i have also been charged with measuring ethanol in solution. Obviously i would have to use a different solvent to dilute, but which one could i use and which one would i have to avoid.

Sorry if these questions are a little simplistic as i know we have some very experienced people in here.

The one question that has an answer is why the solvent does not overload the detector. It is because the filament of the MS is kept switched off until the solvent peak has eluted - say for the first 3 min or so of the run (or longer if the peak you are interested in elutes later. This prolongs filament lifetime.

The other questions cannot be answered unless we know what the target analytes are dissolved in to start with - what is your sample matrix ?

Peter

The one question that has an answer is why the solvent does not overload the detector. It is because the filament of the MS is kept switched off until the solvent peak has eluted - say for the first 3 min or so of the run (or longer if the peak you are interested in elutes later. This prolongs filament lifetime.

The other questions cannot be answered unless we know what the target analytes are dissolved in to start with - what is your sample matrix ?

Peter

Hi Peter, thanks for that. The ethyl lactate is part of a product produced by reacting sodium lactate with ethanol (and Co2) Sodium Bicarbonate is also formed and seperated leaving the ethyl lactate, ethanol mix.

John

Hi John

Are you wanting ethanol and ethyl lactate content on the same sample ?, and about how much of each is there in % terms ?

What column do you have in the GC-MS ?

Peter

Well not nescessarily but in an ideal world, the two would be good. I have it in my head that would have to do headspace for the ethanol and im not ready to figure that out yet.

I think we ranging from 50% to 90% ethyl lactate, the rest is ethanol.

I have a Rxi®-5ms Columns (fused silica). (low polarity phase; Crossbond® diphenyl dimethyl polysiloxane) in. A bit of arbitrary choice.

JC

Direct injection, smallest volume practical, 0.5ul (?) , split injection with split ratio of 500:1

You have been asked to carry out bucket chemistry with a device designed to work with nanograms

Hope it's a thick film column ? >1um film ?

Would be an application for an old packed column GC with FID

A decade ago we had some USP glycerin that got contaminated after leaving the facility to get packed into drums. I identified the contaminant as ethyl lactate, and we developed procedures to quantify it both by capillary GC and by non-suppressed ion chromatography (after saponification).

Since glycerin is VERY polar, we used a USP G43 column, like Rtx-624 or other "624" column. We also use similar 624 column for ethanol determinations, like in USP <611>. So even though ethyl lactate is not polar, you may be able to do both on same column, programming the oven up for ethyl lactate to elute. I'd first try methanol as solvent, 624 will resolve methanol readily from ethanol at temperatures like 40C. You may get a little tailing, as this column is not the best match for either ethyl lactate or for ethanol (yes, I know it's in the USP procedure for ethanol, just saying....).