Chromatography Forum

I am trying to measure nicotine in glycerol/ethanol. The response factor is about 3x low when it is
in glycerol compared to when it is in just ethanol. I'm using .5 uL 100:1 split on a DB624 column
44 cm/sec; inlet 250. I can see the glycerol emerge as a wide hump around the nicotine.

Anybody know what is going on? I think maybe the inlet is getting coated with glycerin and that
it captures some of the nicotine. Temp is 220 to 240 at 20C/min then 1 minute hold.

Perhaps all of the nicotine doesn't get out of the glycerol in a timely manner in your injection. The b.p. for glycerol is 290 °C. Your inlet temperature is too low for that solvent.

Anybody know what is going on? I think maybe the inlet is getting coated with glycerin and that
it captures some of the nicotine. Temp is 220 to 240 at 20C/min then 1 minute hold.

Is this your oven program?

It would be helpful to know what size of syringe you are using, dwell time and if it is a manual injection.

One possibility is incomplete evaporation of glycerine from the needle
If it is a manual injection with a 10uL syringe then the needle volume is about 0.8 uL. Under these conditions the total volume injected with ethanol is 1.3uL if the needle content is evaporated as well. With glycerin the needle volume may not be evaporated so 0.5uL is injected.

Try priming your syringe with 1uL of ethanol, then draw back to produce a 1uL air gap then draw back 0.5uL with the glycerine sample. This way the needle volume is flushed out on injection. Also raise your Injection temp to 320°C.

Use the same procedure with the ethanol sample and compare

A 100:1 split implies sensitivity to spare. Try diluting both types of sample in ethanol; say 20:1, to decrease the difference in matrix. Increase the inlet temperature as high as you can to shift the glycerol.

Peter

Glycerol is very viscous and difficult to syringe accurately. Peter's suggestion would overcome that and allow for matrix matching and improve mobility

Following a 20:1 dilution you can

1. Use a split ratio of 10:1
2. Inject 1uL

A combination of dilution, increasing the dwell time of your syringe needle in the injection port at a higher temperature and using 1uL instead of 0.5uL you will achieve the same sample injection amount and get better precision

Let us know how you get on

Also adding a viscosity delay on your auto sampler is a good idea. I would also agree to dilute the sample but if your starting GC temp is that high I'd recommend xylene or toluene over ethanol. Having a starting temp that far above the boiling temperature of the solvent could cause artifcats plus ethanol and methanol have a higher inlet expansion and hold more polars than toluene or xylene.

And, be sure you are using a liner that will catch droplets of this sample and allow them to evaporate! I have a preference for a glass wool plug for this type of analysis.