Chromatography Forum

I have a GC-8A Shimadzu with Nitrogen as a carrier gas.
I tried to calibrate methanol and ethanol with propanol as an internal standard.
The ethanol and propanol peaks are coming out, unfortunately the methanol peak isn't coming out at all.
can somebody help please. Thank you

What detector? What column and its conditions? What sample preparation conditions?

Rod

the injector/detector temp is 130 C, column temp 80 C, carrier gas (N2) 130.
The column made from stainless steel 1/8", 2.0M packed with 0.2% carbowax 1500 on 80-100 mesh carbopack C.
The sample standard that I injected is 10 percent ethanol standard with 0.01% methanol.
Thank you very much for your attention.

What detector? TCD FID

Carrier is 130cc/min ???

100 ppm of methanol in ethanol is TINY

Methanol is easily lost from a preparation if open to the atmosphere for a few minutes, even at % levels.

Ethanol peak may easily overload the column and methanol peak can be lost at the front of the ethanol peak.

Slow your column flow rate and reduce the size of your injection.

good luck,

ROd

ingewirawan,

10% ethanol, 0.01% methanol, and the balance is???

Best regards,

AICMM

My GC is FID. And I'm using 0.2% propanol as an internal standard.
The carrier gas (N2) is 130psi.
@Mr.Rod, how to slow the column flow rate? Right now, I used 0.1ul sample.
Thank you so much for your help.

Inge

Reduce your pressure from 130 psi to 65 psi. That will greatly reduce the flow rate through your column.

Keep your injection size the same.

Good luck,

Rod

I agree that 100 ppm is a very small quantity and so is 0.1 µl injection.
If you reduce the carrier flow it can happens that you will need a make-up flow at the FID.
As suggestion, Increase the volume to 1 µl keep the injector port at 130°C but reduce the oven temperature to 40°C (or less if you can) wait the Methanol and Ethanol peaks and then Temp program to 80 or 100°C.
I'm using a Capillary column to analyze Methanol but I also need to separate it from Ethyl Acetate. So my oven temp is 45°C

Even at 65 psi with a 2 meter packed column there will be no need for makeup gas at the FID.

Reducing the oven temp to better separate methanol from ethanol is a good recommendation, but hopefully only a reduction in carrier flow will be necessary.

I hope the problem is not a damaged packed column as Carbopack C requires careful handling.

best wishes,

Rod

Dear all, thank you for paying attention for my problem .
For the last three days, I tried everything that you've suggested, like reduced the carrier gas, reduced the column and injector temperature down, increased the concentration of methanol to 1000ppm, and I also clean the injection port.
Unfortunately, I still not getting the peak for methanol .
I'm really frustated right now.
But, I'm really grateful that all of you have tried to help me.
Thank you very much

I guess we're missing some keys facts here: What is your solution comprised of? Please give a complete breakdown.

And Rod is right: Those huge amounts of ethanol can easily overload a column and obscure your Methanol peak.

Now regarding your setup: Are you using a liner? If not, I urgently advice to do so.
And what about your flow rates? 65 psi for a 2 m column seems quite oversized to me. High flow rates degrade separation, especially on shorter columns where you don't need high flow to minimize diffusion caused by the particles in the packed column.
Better use smaller flows (around 15 ml/min) and compensate with make-up on the FID.

To check your setup, I'd prepare a 0.2% solution of Methanol in your solvent (which is...?) and inject 0.1 yl, 0.5yl and 1yl.
Now check if you see MeOH at all.

You should also post some chromatograms so we can check for anomalies.

I would try using a porous polymer column1-2 meters in length.

I would not be surprised if you lose your methanol peak because it has evaporated out of your mix.

You really should use a test mix with a percent level of methanol or even a neat injection of methanol.

And you should use a std that almost completely fills its vessel so there is a minimum or no headspace in the vial.

First determine that the methanol does separate from your ethanol peak. Your problem should not be all that difficult to solve.

good luck,

Rod

Have you tried placing ethanol, methanol, and propanol in hexadecane as a standard?? Since you are not using a mass spec, but a FID override any solvent delay.

Yesterday, I tried to make a standard with 1% methanol and 10% methanol in the 0.2% propanol standard. Finally, the peak is coming up.
But, after I injected with my sample (wine), the methanol peak is not coming out at all.
Because wine is usually has a very small amount of methanol (0.01%-0.1%) and high on ethanol (10%-20%)

I tried to do two standard methanol-ethanol solution:
1. 10% ethanol with 100 ppm methanol standard
2. 20% ethanol with 1000 ppm methanol standard
And I'm using 0.2% propanol as an internal standard.
The vial preparation that I prepared is using a diluter with
250uL (ethanol/methanol standard):2500uL(propanol internal standard). And I inject 1 uL to the GC.
Thank you so much.

Sincerely,
Inge

How many samples have you injected upon this column? How many injections do you think you can inject before you replace the column?

Do you use a precolumn? If so have you replaced it lately?

How much methanol do you think you can get to pass through deposits of wine at the head of the column?

Do you have to use this column type? Can you replace it with another column?

best wishes,

Rod