gas chromatography is all the separation of chemicals based upon their behavior as gases
The standard procedure is, of course, to inject a liquid into the GC
the liquid would typically be a solvent type material carrying the analytes
this small amount of liquid... like a microliter, is injected into a heated space
The heated space immediately vaporizes everything and then is then swept into the column as gases
and separated as gases
For some low boiling analytes, you can just inject gas as a gas
and don't even do the liquid business at all
one of the approaches that uses this is called headspace gas chromatography
the basic idea is to put the sample in... like a test tube
heat the test tube up a little bit and then inject the vapors over the liquid
using a regular syringe ....Just inject gas, the headspace, which is over the liquid
just inject the headspace itself ...don't do liquid at all
headspace can be used for small alcohols.... up to about C5
small carboxylic acids like fatty acids up to... again ...to about C5
or maybe as high as C7... small amines..... alcohols
we look at this chromatogram and we can see for example for this one that it
has ethyl butyrate , isoamyl acetate, ethyliso valerate
benzaldehyde which is an aromatic compound
but this is a flavoring standard for chocolate
maybe you could use it for ...like... fermentation like for beer for wine.. perhaps
here's one that has ...this sort of looks like hazardous waste
methyl ethyl ketone ....ethanol I think would be a peak about right here
methanol ....isopropanol... ethyl acetate .... methyl ethyl ketone, n-propanol comes out of this scan
benzene ...styrene... ethyl benzene... all the xylenes would come out on this one...
and then this one shows chlorinated hydrocarbons like carbon tetrachloride, ethylbenzene,
diethyl benzene, methylene chloride and things like that will come out on this....acetone
so there's a wide variety of things that you can analyze with headspace gas chromatography
this approach is usually done with an autosampler
the autosampler uses small proprietary bottles
they're about maybe 10 milliliters a piece or something like that
the sample aliquoted, with an internal standard, into these vials
the vials in the autosampler are pulled up... like... into a heated turret or something like that
they kind of disappear into the instrument and then, according to the computer, controlled by the operator
they're heated up for a certain period of time and then injected for a certain period of time
it's ....it's my image of it is.... it's usually automated with an autosampler
the autosampler will be heating like one and two and three samples at a time
and then at the same time it's analyzing one so it is constantly cycling them
through the heating phase and then into the analysis phase
some of the autosamplers have a mechanism for shaking the sample immediately before it's injected
I worked in a toxicology environment for quite a few years I worked in two different laboratories
the first laboratory was a hard-core clinical toxicology laboratory
supporting police departments, coroners, emergency rooms
we did things like forensic specimens (on) for coroners the police find somebody passed out in the street
and they want to know what kind of drugs they are under
somebody has a poisoning or suspected poisoning things like that
we did about ..... the laboratory did about fifty ethanol quantitations a week
I would do maybe two to three on my shift every night
we did them by hand, We just pipetted the internal standard and the sample into a tube
put little rubber stopper on it and put it in a heating block and then inject it
into the GC using an ordinary syringe with the Luer lock needle on it.
inject maybe a half a mill or something like that this is all done with an internal standard
so you would aliquot your sample and internal standard
control... standard and sample... sample ....sample
just inject them by hand the signal went into a strip chart recorder
we just measured peak height and did it manually it wasn't really a problem
We did not do that many of them
later on I started working in a big medical laboratory and a lot of my responsibility
was doing forensic blood alcohols for police departments like drunken drivers
the police would send a kit containing two blood samples ... really directly to me
and I would open and treat them just by myself... no intervention from the laboratory around me
but I had an autosampler that took care of everything
and then the autosampler had a little tabletop integrator which did all work for me
the samples were run in duplicate.... the analysis was amazingly precise and amazingly accurate
you have to constant monitor on the quality of the analysis based upon the duplicate results
if the duplicates are coming out the same sample after sample
you have very confident assurance that the analysis is precise and accurate
I had an autopipettor which would very precisely.... very reproducibly
portion out the internal standard and the sample
and I think that was a lot of the key to the precision of the analysis
it wasn't particularly to my credit... It was more to the fact that I had very good equipment
and ....during those years I did probably thousands ...tens of thousands of injections
and never had a problem with it
I would aliquot them into their proprietary tubes, ...
did a septum seal and they disappeared into the instrument and came out ...
the results came out on the strip chart recorder (integrator)
And I would process them and send the report to the police departments
and testified in court... not extremely often, but very regularly for number of years
sometimes I think that there are is not enough cross-pollination in science
if you're doing a research project or any kind of quality control project
look at your analytes and if they're very volatile consider doing upon it by headspace
you can do the method development by hand ... get a heating seating block and some test tubes
aliquot a sample plus an internal standard into the test tubes maybe a mill to two milliliters total
just put some parafilm on top.... put them in the heating block
and just do the injection by hand...about half a mill with a regular syringe
and see what you get and if the results look promising go to your managers see you can't scare up some money
to buy an autosampler. The autosamplers are expensive, but they are very robust and they'll last a long time
the precision of the headspace analysis with an internal standard
if it's done carefully is better than anything I personally have ever seen