Chromatography Forum

Good day!
Does anybody know the method of GC Test for Residual Ethanol in Diethyl Malonate, including sample preparation and all the test parameter?
Really appreciate if someone could give some information.
Thanks.

Dan

Did you research to see if a test procedure already exists? What levels of ethanol would you be expecting? 100ppm or 1% is a huge difference.

My thoughts otherwise would be headspace, or diluting/mixing with water and a polar capillary. Maybe even adding n-propyl alcohol as internal standard.

Most of our ethanol assays here are for 67% to 3% levels, in consumer products.

First, you could run this product for solvents by headspace. Since it is a liquid that boils at a high temperature, it should not be a problem to put 50 or 100 microliters into a headspace vial and run it neat with 3 std additions in DMF or DMSO (don't forget to add blank DMF or DMSO to your 0 ppm spike)

IT is unlikely you have much ethanol present since the boiling points are SO different it should be easy to separate EtOH and DEM. Unless of course, the DEM is degraded from the presence of water and over time.

You could also run this test as a v/v test injecting directly onto a column such as a porous polymer column.

Methanol, ethanol, n-propanol should all elute before DEM. If you do it v/v use a suitable late eluting solvent for your stds (toluene comes to mind).

I would run the column isothermally at 180°C, with injector at 200°C and detector at 250°C

Headspace could be done isothermally at 80°C

best wishes,

Rod

Did you research to see if a test procedure already exists? What levels of ethanol would you be expecting? 100ppm or 1% is a huge difference.

My thoughts otherwise would be headspace, or diluting/mixing with water and a polar capillary. Maybe even adding n-propyl alcohol as internal standard.

Most of our ethanol assays here are for 67% to 3% levels, in consumer products.

Thanks for your time, the level of ethanol is below 100ppm.

First, you could run this product for solvents by headspace. Since it is a liquid that boils at a high temperature, it should not be a problem to put 50 or 100 microliters into a headspace vial and run it neat with 3 std additions in DMF or DMSO (don't forget to add blank DMF or DMSO to your 0 ppm spike)

IT is unlikely you have much ethanol present since the boiling points are SO different it should be easy to separate EtOH and DEM. Unless of course, the DEM is degraded from the presence of water and over time.

You could also run this test as a v/v test injecting directly onto a column such as a porous polymer column.

Methanol, ethanol, n-propanol should all elute before DEM. If you do it v/v use a suitable late eluting solvent for your stds (toluene comes to mind).

I would run the column isothermally at 180°C, with injector at 200°C and detector at 250°C

Headspace could be done isothermally at 80°C

best wishes,

Rod

Hi Rod, really thank you very much for detailed explanation and information.
To be frank, I am sales manager of our company, so I only know little about the test, actually we don't have to have this kind of test for our DEM and DEMM products before, one of our overseas client is now requesting this from me, so I am seeking some information on internet and from experts like you.
Actually I also found something with very detailed information like Chromatography conditions, Sample preparation, Operation procedure and System adaptability, but our client said they followed that method, but failed, so if you could give me some information or revision to the below method, that will be greatly appreciated. Daniel

HEADSPACE GAS CHROMATOGRAPHY TEST FOR RESIDULE ETHANOL

Chromatography conditions：
Chromatography Column：DB624，30m×0.53mm×3um or 30m×0.32mm×1.8um
Carrier gas: N2 or He
Flow speed: 35cm/s
Split Ratio: 1:5
Headspace temperature: sample vial temperature 80℃, sample loop temperature 105℃, transfer line temperature 105℃
Sample conditions: heating balance 45min，sampler vial pressurization 0.5min，sampling 1.0min
oven temperature：40℃ keep 20min， 20℃/minheating up to 240℃，keep 20min (may reduce properly)
Detector: FID，temperature 250℃，inlet temperature 140℃。

Sample preparation:
Sample solution: Accurately weigh 0.5g sample，use DMF to dissolve and dilute to 50ml
Solvent solution: Accurately weigh 0.5g ethanol，use water to dilute to 100ml，Accurately weigh 1.0ml diluted solution，use water to dilute to 100ml
Blank solvent：use Solvent solution method to prepare blank solvent，but without ethanol
Sample：Accurately weigh 5.0ml sample solution+1.0ml blank solution (3 parallel samples)
Reference sample A：Accurately weight 5.0ml sample solution+1.0ml solvent solution (3 parallel samples)
Reference sample B：Accurately weight 5.0ml DMF+1.0ml blank solution

Operation procedure:
—Reference sample B inlet
—Reference sample A inlet
—Sample inlet

System adaptability:
Reference sample A’s 3 syringes peak area relative standard deviation must be lower than 5.0%

Since your sample is liquid I would inject it directly and determine the amount of ethanol present.

I would take 3x5mL portions and add 0, 1, and 3 µL of ethanol to the three preparations, that is ~5gm portions and adding zero mg, 0.79mg and 2.37mg of ethanol: zero ppm, 158 ppm, and 473 ppm spikes.

Mix thoroughly in a capped vial. Then inject THE SAME AMOUNT OF (1µL) using a Chaney adapter of all three samples using a GC with 200°C injector, 250°C FID detector.

The columns listed would work fine, but a Wax column would also suffice.

Take the areas of the ethanol peaks found and do a linear regression. Determine the x-intercept of the regression line to determine the amount of ethanol present.

HEADSPACE METHOD

The headspace analysis has too much sample (500 mg), heats the sample for too long a time.

Take the three preparations listed above at 0, 158, and 473 ppm spiked and place 50µL into each of 3 headspace vials.

Heat the samples no more than 15 and no less than 8 minutes. Timed injection should be 0.05min or less, not 1 min ! No wonder it failed. If you use a sample loop use 0.25mL loop. The conditions you have listed are fine.

Good luck,

ROd

Hi Rod,
Really thank you very much for your detailed reply.
I have already transfer your advice to our lab staff and our client, hope the test could be finished in the right way.
Once again thank you very much for your time and patience.
Daniel