temperature programming in gc

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Temperatureprogramming in GC

Training course on GC/MS

Nha Trang 13-18/10 2008

Charlotta Rylander



Separation of compounds by

GC

In GC, analytes are separated according to boiling

point and polarity and other properties.

The boiling point affect how easily the analytes

evaporate. Molecules with low boiling point will eluteearly from the GC column, hence, compounds with

high boiling point will elute late.

Analytes interact with the GC column. If the column

is non-polar, analytes with high polarity will travelfast through the column while more non-polar

compounds will be retained.



Temperature effects

Temperature

Retention time

Vapour pressure of analytes Partitioningcoefficient



Isothermal column

temperature If the GC is run isothermally, the

column temperature is constantthroughout the analysis.

Fast eluting compounds may then

appear as overlapping peaks andlate eluting compounds will havelong retention time and broadpeak shape.

Isothermal GC is not a goodchoice for samples containinganalytes with varying boilingpoints.

http://ull.chemistry.uakron.edu/chemsep/slide.php?Ch

apter=/chemsep/GC/&Last=100&Slide=56



Temperature programming

By increasing thetemperature as a functionof time, it is possible to

separate mixtures withvarious boiling point andstill have goodchromatography.

In addition, the totalanalysis time will beshorter.

http://ull.chemistry.uakron.edu/chemsep/slide.php?Ch

apter=/chemsep/GC/&Last=100&Slide=56



Isothermal GC temperature/

Temperature programming

Isotherm column

temperature

Temperature

programming

www.chem.agilent.com



Setting up a temperature

program

Try to find publications about analysis of the

analytes of interest. Usually, the temperature

program is reported.

Useful internet sites:

http://chromatographyonline.findpharma.com/lcgc/

http://spectroscopymag.findpharma.com/spectrosco

py


http://spectroscopymag.findpharma.com/spectroscopy








program

Always use standard solutions whensetting up a temperature program.

The injector temperature must beoptimized before start. If the injectortemperature is too low, the analyteswill not be vaporized. If it is too high,we may loose analytes. Check boilingpoint of analytes before start. Ramptemperature on column whenoptimizing injector temperature.

Take care when using on columndetector. Check the boiling point ofsolvents and solvent mixtures.

http://www.cartage.org.lb/en/themes/Sciences/Chemist

ry/Analyticalchemistry/MethodsInstrumentation/Chrom

atography/Gaschromatography/splitinj.gif




program

Start with ramping the temperature (50°C-300°C, 5-10°C/min, depending on analytes) to make sure youelute all compounds. From that run it is possible todetermine the final temperature of the GC

programme. Identify possible coelutions.

In areas with coelutions, add isothermal periods.

Initial temperature should be determined based on

best possible separation of the the first few peaks. Experiment with various ramps between initial and

final temperature to get the best separation andshortest method.

temperature programming in gc

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