Essential oils dilution for GC trough FID

Discussions about sample preparation: extraction, cleanup, derivatization, etc.

30 posts Page 1 of 2
Hello everyone,

I'm new to GC, i have bought a Varian 3800 with FID, I am just wondering if the Essential oils need dilution or they can be used as they are in the GC process?

Thanks,
/Alvin
Depending on the condition of your detector, I strongly recommend a dilution in dichloromethane. You don't want all of that oil gunking up your inlet liner, column or detector jet.
Don Shelly
LGC Standards
Thanks Don,

What proportion do you recommend?

/Alvin
Depending mainly what column you have in the GC you cannot put any more than 100ng of any component onto the column (end even that is pushing it). So you need to dilute 100:1 and use a split ratio of 20:1 assuming you have 5 major components in the oil. The more complicated the oil, the less you need to dilute.

Peter
Peter Apps
Peter Apps wrote:
Depending mainly what column you have in the GC you cannot put any more than 100ng of any component onto the column (end even that is pushing it). So you need to dilute 100:1 and use a split ratio of 20:1 assuming you have 5 major components in the oil. The more complicated the oil, the less you need to dilute.

Peter



Thanks Peter,

The column is 10m long. I wonder if it works if I dilute first the essential oil in 99,5% alcohol and then dilute again with distilled water?
I'm using a Varian 3800 with autosampler.
ant78se wrote:
Peter Apps wrote:
Depending mainly what column you have in the GC you cannot put any more than 100ng of any component onto the column (end even that is pushing it). So you need to dilute 100:1 and use a split ratio of 20:1 assuming you have 5 major components in the oil. The more complicated the oil, the less you need to dilute.

Peter



Thanks Peter,

The column is 10m long. I wonder if it works if I dilute first the essential oil in 99,5% alcohol and then dilute again with distilled water?
I'm using a Varian 3800 with autosampler.


It is the diameter and stationary phase film thickness and type rather than the length that determine how much sample you can load onto a column.

10 m is rather short for complex natural mixtures like essential oils.

Do not use water to dilute the samples - it will cause all kinds of problems.

Peter
Peter Apps
It's best to choose a highly volatile solvent. The solvent needs to "flash" in the injection port and also precede your analytes through the column so as not to interfere with the resolution of your analytes. That's why I recommended DCM. Essential oils should be miscible in DCM and DCM is very volatile and less likely to be retained by your stationary phase.

I agree with Peter that 10 meters is a very short column if you are looking for resolution of all of your components.

Do you know the stationary phase of the column?
Don Shelly
LGC Standards
Don Shelly wrote:
It's best to choose a highly volatile solvent. The solvent needs to "flash" in the injection port and also precede your analytes through the column so as not to interfere with the resolution of your analytes. That's why I recommended DCM. Essential oils should be miscible in DCM and DCM is very volatile and less likely to be retained by your stationary phase.

I agree with Peter that 10 meters is a very short column if you are looking for resolution of all of your components.

Do you know the stationary phase of the column?


Hi Don,

I will post all the details about the GC as soon it arrives from UK.
I checked the price of DCM is more expensive than 99,5 % alcohol that i all ready have.
I can also blend some nice pinacoladas in the same time as i dilute for the GC =)
As long as the alcohol doesn't co-elute with the essential oils you're okay. The pina colada should make your chromatography experience more enjoyable. I will need to test that out sometime. 8)
Don Shelly
LGC Standards
Hi

Without wishing to go off topic ( and I know that I just have :) )

Use 95% alcohol for your pina colada . The 99+% used to be produced by co-distilling with benzene and when I analysed it by LVI I found huge amounts of aromatics present. The 95% is just produced by distillation and is actually far cleaner with only water as the major impurity.

So this is why I "borrowed" only the 95% when making Sloe Gin.

It still needs diluting afterwards

Regards

Ralph
Regards

Ralph
Thanks Ralph, that's about the most useful thing anyone has ever posted on the forum !! :P

Peter
Peter Apps
Don Shelly wrote:
It's best to choose a highly volatile solvent. The solvent needs to "flash" in the injection port and also precede your analytes through the column so as not to interfere with the resolution of your analytes. That's why I recommended DCM. Essential oils should be miscible in DCM and DCM is very volatile and less likely to be retained by your stationary phase.

I agree with Peter that 10 meters is a very short column if you are looking for resolution of all of your components.

Do you know the stationary phase of the column?


Hi Don,

Now i've got my GC delivered. It has 2 FID's and two columns (cat no. 6172 25m 0,25mm 0,2um) but one coulmn is broken about 10cm from the connection to FID.
Image
Image
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Now i'm wondering if i should buy a longer column or it has to be the same type and length?

Cheers!!
/Alvin
Hi Alvin,

How many inlets does it have ? - are both the columns connected to one inlet, or do they go to separate inlets ?

Peter
Peter Apps
Peter Apps wrote:
Hi Alvin,

How many inlets does it have ? - are both the columns connected to one inlet, or do they go to separate inlets ?

Peter


Hi Peter,

I didn't had too much time but I'll check and post later.
It's one inlet from the autosampler and i think it's a splitter inside that goes to the two columns.
Image

/Alvin
Alvin, Please post picture of what is inside the oven.

I am almost certain that the two columns will have different stationary phases.

My suggestion is that you run with only one column until your familialr with the hardware and software, and then go to two columns if you need to.

Peter
Peter Apps
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