Gas-liquid and HP Liquid Chromatography

[lepellillow]

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identify, outline and assess the value of the following techniques in the analysis of small samples:
- gas-liquid chromatography
- high performance liquid chromatography


so i know how both of them work, pretty much, but what is the value of them? like is it just meaning the value of chromatography in general? or should we know which is more useful for specific substances to analyse or what? silly dot point!!

[rodders1]

Originally Posted by lepellillow

identify, outline and assess the value of the following techniques in the analysis of small samples:
- gas-liquid chromatography
- high performance liquid chromatography


so i know how both of them work, pretty much, but what is the value of them? like is it just meaning the value of chromatography in general? or should we know which is more useful for specific substances to analyse or what? silly dot point!!

So, value refers to the significance of its existence. So both techniques allow a mixture to be separated into it components. This has had a large impact on forensic investigations etc. You might also like to go into the individual strengths of the two different techniques, for example GC is quick (10 min per sample this allows evidence to be processed quickly) and HPLC is able to process thermally unstable and volatile compounds.
I think that the small sample part of the question speaks for itself. You would need to mention that both are extremely sensitive and measure to ppm and ppm.

[-::Sanni::-]

Originally Posted by rodders1

ppm and ppm

ppm and ppb?


How does gas and high performance liquid chromatography work? How much detail will we need to go into?

This is what I know of them...

Gas Chromatography:
Moving phase: carrier gas

Stationary phase: liquid on the sides of the tube

Advantage: fast

Disadvantage: need high temperatures to operate

HP liquid Chromatography:
Moving phase: liquid pumped into colum with solid particles

Stationary phase: surface of solid particles (chemically treated) in the column

Advantage: fast; can test substances that are heat sensitive unlike gas chromatography.

Disadvantage: cost of equipment


What else do we need to know?

[j-3-s-5]

Originally Posted by -::Sanni::-

What else do we need to know?

Uses:

GLC- identify pesticide recidues in food, detecting illegal drugs or performancing enhancing drugs in athletes, trace pollutants inair and water, and other substances at crime scenes.

HPLC- Same as GLC, but also detecting traces of explosives, and analysis biological samples such as polypeptides from proteins.

[wixxy2348]

Ok so my teacher was going on about TLC (thin layer chromatography) and got us to include it in one of our summaries...
Is it actualy necessary to know about it?

[Alchemist K]

Originally Posted by wixxy2348

Ok so my teacher was going on about TLC (thin layer chromatography) and got us to include it in one of our summaries...
Is it actualy necessary to know about it?

Yeah, why not? TLC is basically a quick way of checking what's in a mixture. For HPLC and GC the whole process is really tedious, needs a lot of washing and waiting whereas for TLC its much quicker. However, TLC is less accurate in terms of quantitative measurements although, quantitiative TLC does exist where machines can accurately dispense amounts of solution to the plate.

In labs, TLCs are often performed as preliminary testing e.g. to identify the appropriate solvent system before more time and effort is put into HPLC and GC.

[britt-eck]

[quote=Alchemist K;4140517] For HPLC and GC the whole process is really tedious, needs a lot of washing and waiting whereas for TLC its much quicker.

what do you mean that they need a lot of washing and waiting???

[brenton1987]

Originally Posted by britt-eck

what do you mean that they need a lot of washing and waiting???

There is the waiting for the column to heat up and the time it takes for the sample to move through the column.

After each sample has come through the column the carrier medium flows through the column for a period of time to remove any traces.

[marcquelle]

Originally Posted by -::Sanni::-

ppm and ppb?

Particles per Million, Particles per Billion

With the range of solvents experiment what did you guys do, our teacher just made us to different concentrations of methanol and water *is that ok?*