- GC Specially GLC involves a sample being vapourized and injected on to the head. of the chromatography columm
- The sample is transpotted through the column by the flow of inert goses mobile Phase the column it self contain a liquid Stationary phase which is adsorb on to the surface of an inert solid.
> Instotumentation
- Although many commerical variation are available badsically all GC whenther GLC & GSC consist of six basic component.
1) A carrier gas
2) A Sample imjection system
3) The Separation column
4) One or:more detector
5) Thermostate: chamber for the temp. & regulation of the columm & detestor
6) A amplification & recorder system
1) A Carrier gas
- The carrier gas must be chemintcally inert
- commonlly used gases include N²,Ar & CO²
- The choice carrier gas is of ten depend ant upon the types of detector which is used
- The carrier gas system also comtain molecular to remove water & other impurite
- Here He is generally used because of it excellent thermal conductivity inertness low density & it allows greater flow rates .
- H-has a better thermal conductivity & low density but has the disadvantages that it may react with compound & that is Crecte, a fire & explosive hazard
- For Selecting a carrier gas following consideulation Should be taken into account
I) It should be inert in othereword it should not react with the sample Stationary phase or contacted hardware.
II) It Should be suitable for the detectar amployed & the types of sample analyzed.
III) it Shoud be readily availabie in high puulty.
IV) It should be a cheap
V) It should not cost the risk of fire or explosion hezand
2) A Sample infection system
- For optimum columm efficiency the sample should not be too large & shoule be introduced on to the columm as a plug of vapor slow injection of large sample causis band brodening & losses of the resolution..
- The most common imjection method is where a micro Serenge is used to inject to sample through a rubber in to a flash vaporzer port at the head of the columm.
- For pack columm sample size ranges from 10th of micro liter upto 20 micro liter
- capillaory columm on the other hand need much less sample typically around 10micro liter
Fout capillary GC Split/Splitless in ion is used.
3) The Seperation Columm
- There qre gejenally two types of columm Pack columm & capillamy columm also known as tabular
- pack columm contain a finally devided inerct solid support of material comm only base on dialomaceous earth cated with liquid Statonary phase.
- Most pack columm are 1.5 to 10 m in length & have an internal diameter of 2 to 4 mm.
- capillary have an internal chamber of a few 1oth of milimeteu
> They can be one of two types
I) woll coateel open tabular (WCOT) II) support coated open tabular (SCOT)
- woll Coated column consist of a capillary tube whose woll are coated with liquid stationary phase.
- In supporl coated columm of the inner wall a suppor molecule such as a earth in to which the stationary phase hos been adsoubed
- SCOT columm are genenauy less efficient then WCOT columm.
- Both types of capillary columm are more efficient than pack columm.
4) Colum Temperature
- For Precious work columm temperature ture must be contorol to within leguthe of degree
- The optimum columm temperature dependent upon the boiling point of the sample .
- As a roll of them at a tempereture Slightly above, the average boiling point sample
- Minimum temp. give good resolution but incurease elution time
- If a sample has a whide boling then temp. programining can be usefil
- The column temp is incorease as a
sepauiation proceed.
Superb
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