novice questions: why is my chromatogram periodic?

[glenchung]

Cool idea for the 1-mL syringe, thanks very much Peter, I will do it.

[James_Ball]

Peter has a good idea there.

The only other option with a 1ml syringe would be doing headspace analysis. Take a few drops of gasoline and put it into a 10-50ml vial with some type of septa, allow it to evaporate, then pull 1ml of the gas from the headspace in the vial and inject the whole 1ml of gas slowly into the injection port with the column at about 40C, then ramp to about 250C over 15 minutes and look for the pattern to appear. If you are doing this for demonstration purposes in a school chemistry class that would be a good experiment also.

[glenchung]

Wow, another cool idea. James_Ball, would that headspace routine be repeatable? Is this something that you industry types do often, for quick and qualitative analyses?

[rb6banjo]

Headspace analysis is all I do - pretty much. I have found that manual injection headspace analysis can be somewhat lacking when it comes to reproducibility. Autosamplers designed for headspace analysis help to improve this.

Typically, to get good results from a quantitative standpoint, you need specially designed vials where your sample is contained inside, there is a septum on the vial that you can pierce with the needle of your syringe to extract the sample. Most of us use something like this:

http://i1285.photobucket.com/albums/a59 ... 39b231.gif

The cap is a piece of aluminum with a hole in the center. A rubber septum (gasket) fits tightly in the cap and is crimped down on the flange of the glass vial. The rubber gasket seals the sample inside and allows a path for the syringe needle to get into the vapor space of the vial to pull out a sample.

There are other sizes. You can use other things as well. If you are just doing qualitative analysis, you can inject into a ziploc bag that contains your gas sample (go grab some exhaust from a car in the parking lot, don't burn yourself!!!). Throw some flowers in the bag, let it sit for a while, then reach in with the syringe and get a sample of the gas. There are other things you have to worry about when you use polymeric bags, e.g., does the bag absorb or react with your analytes?, etc. You are only limited by your imagination.

I wish my high school would have had a GC when I was there.

[glenchung]

Those are fabulous ideas, rb6banjo, thank you very much. I will try the car exhaust idea somehow.

[rb6banjo]

You're welcome. Like I said, don't burn yourself. That pipe gets really hot if the car is on for a while.

[KM-USA]

You are only limited by your imagination.

We've put an (unused) non-lubricated condom over an aerosol can, then sprayed itno that to get gas sample for GCMS to determine which propellant was used.

[rb6banjo]

That's very creative!!! I wouldn't have thought of that one.

[James_Ball]

You are only limited by your imagination.

We've put an (unused) non-lubricated condom over an aerosol can, then sprayed itno that to get gas sample for GCMS to determine which propellant was used.

I can just imagine the reaction from a room full of teenagers when you try that one

[Steve Reimer]

Who needs Tedlar bags anyway?