Gas chromatography (1)

Principle, instrumentation and application of gas chromatography

1. GAS CHROMATOGRAPHY
Prepared By:-
Mr. LokeshThote
Asstt. Professor
Department of Pharmaceutical
Chemistry
Kamla Nehru
College of Pharmacy,
Butibori, Nagpur (M.S.)

2. Introduction
*Gaschromatography–Itisaprocessofseparating
component(s)fromthegivencrudedrugormixturebyusing
stationaryphase(solidorliquid)andgaseousmobilephase.
*Itinvolvesasamplebeingvaporizedandinjectedontotheheadof
thechromatographiccolumn.Thesampleistransportedthroughthe
columnbytheflowofinert,gaseousmobilephase.
*Thecolumnitselfcontainsasolidorliquidstationaryphasewhich
isadsorbedontothesurfaceofaninertsolid.
*Twomajortypes
•Gas-solidchromatography(GSC)
(Stationaryphase:solid)
•Gas-liquidchromatography(GLC)
(Stationaryphase:immobilizedliquid)

3. AdvantagesofGasChromatography
*Thetechniquehasstrongseparationpowerandevencomplex
mixturecanberesolvedintoconstituents
*Thesensitivityofthemethodisquitehigh.itismicromethodonly
fewmgofsampleissufficientforanalysis.
*Itgivesgoodprecisionandaccuracy
*Theanalysisiscompletedinashorttime
*Thecostofinstrumentisrelativelylowanditslifeisgenerallylong
*Thetechniqueisrelativelysuitableforroutineanalysis(donot
requirehighlyskilledpersonforoperation)

4. Components ofGas chromatograph.
1.Carriergas:-He(common),N2,H2,Argon.
2.Flow regulators & Flowmeters
Sampleinjectionport:-
Columns:-2-50m coiledstainlesssteel/glass/Teflon.
3.Detectors:-Flameionization(FID),Thermalconductivity
(TCD),Electroncapture(ECD),Nitrogen-phosphorus,Flame
photometric(FPD),Photo-ionization(PID).
4.Thermostatchamber:-fortemperatureregulationofthe
columnanddetectors.
5.Anamplifierandrecordingsystem

5. Schematic diagram of Gas Chromatograph

7. 1. Carrier gas
Thecarriergasmustbechemicallyinert.
Commonlyusedgasesincludehydrogen,nitrogen,helium,argon,and
carbondioxide.
Hydrogenhasmoreadvantagesascomparedtoothersbutithighly
flammable.
Heliumisgenerallyusedbecauseofitsexcellentthermal
conductivity,inertness,lowdensityandallowhighflowrate.
Thechoiceofcarriergasisoftendependantuponthetypeofdetector
whichisused.
Forselectingcarrierfollowingthingshouldbeconsider
o Itshouldbeinert
o Shouldbesuitablefordetectors.Nofireorexplosionhazards
o Readilyavailableinhighpurity.Shouldbecheap.

8. 2. Flow regulators & Flow meters
Deliver the gas with uniform pressure/flow rate
flow meters:-Rota meter & Soap bubble flow meter
ROTA METER
Placed before column inlet
It has a glass tube with a float
held on to a spring.
The level of the float is
determined by the flow rate
of carrier gas

9. SOAP BUBBLE METER
SimilartoRotameterbutinsteadofafloat,soapbubbleformed
indicatestheflowrate

10. 3.Sampleinjectionport:
oThemostcommonmethodofsampleinjectioninvolvestheuseof
microsyringetoinjectaliquidorgaseoussamplethroughaself
sealingsiliconrubberdiaphragmorseptumintoaflashvaporizer
portlocatedattheheadofcolumn.
oThesampleportisgenerally
locatedabutthe50
0
cabovethe
boilingpointofleastvolatile
component.
oToincreasethecolumnefficiency
suitablesizeofsampleshouldbe
selectedandintroducedasaplugof
vapor.Theslowinjectionofover
sizesamplecausesbandbroadening
andpoorresolutionofamixture

11. 4. Gas Chromatography–Columns
Thecolumnisheartinchromatography.Inthecolumnthe
differentsoluteinthevaporizedsampleseparatedfromeachother
byvirtueoftheirdifferentinteractionwiththecolumnpacking.
Thetwotypesofcolumnarecommonlyemployedingas
chromatography.
1.Packedcolumn
2.Capillarycolumn
1.Packedcolumns
arepreparedbypackingmetalareglasstubingwith
finelydivided,inert,solidsupportmaterial(diatomaceous
earth)forGSC.
SolidinertcoatedwithliquidstationaryphaseforGLC.
Mostpackedcolumnsare1.5–10minlengthandhavean
internaldiameterof2-4mm.

12. 2. Capillary columns
Thiscolumnalsoreferredastubularcolumn
Madeupoflongcapillarytubing(30to90meter)inlength
havinguniformandnarrowinternaldiameter(0.025–0.075cm).
Madeupofstainlesssteel,copper,nylonorglassetc.
Insidethewallofcapillarytubingiscoatedwiththeliquid
phaseintheformofthin(0.5–1micron)uniformfilmoninert
solidsupportorcoatedwithinertsolidmaterial.
Therearetwotypeofcapillarycolumn
Opentubularcolumn
Supportcoatedopentubularcolumn

13. •Packed
•Capillary

14. Some Common Stationary phases

15. 5.GC-DETECTORS
Therearemanydetectorswhichcanbeusedingaschromatography
Differentdetectorswillgivedifferenttypesofselectivity.
*Detectorscan begroupedintoconcentrationdependant
detectorsandmassflowdependantdetectors.
*Thesignalfromaconcentrationdependantdetectorisrelatedtothe
concentrationofsoluteinthedetector,anddoesnotusuallydestroy
thesampleDilutionofwithmake-upgaswilllowerthedetectors
response.
*Massflowdependantdetectorsusuallydestroythesample,andthe
signalisrelatedtotherateatwhichsolutemoleculesenterthe
detector.Theresponseofamassflowdependantdetectoris
unaffectedbymake-upgas

16. GC–IDEALDETECTORS
Sensitive (10
-8
-10
-15
g solute/s)
Operate at high T (0-400 °C) S
table and reproducible Linear response
Wide dynamic range
Fast response Simple (reliable)
Nondestructive
Uniform response to all analytes

17. 1.ThermalConductivityDetector(TCD)
Theprincipleofthedetectoristhatthetemperatureandthusresistance
ofthewirethroughwhichcurrentisflowingisdependuponthermal
conductivityofgasinwhichitisimmersed.
Thermalconductivityofgasisafunctionofitscomposition.
Construction&Working
Itconsistoftwochamberofsmallvolumes,madewithinametalblock:
eachcontainingaresistancewirewithhightemperaturecoefficientof
resistance(resistancevariesgreatlywithtemperature).Theseresistance
constituteReference(R)andsensing(S).
Thecarriergasispassesinboththecellandarrangementissuchthatthe
columneffluentaremovedintothesensingsideonly.
Whenasamplecomponententersintosensingcell,thetemperatureofthe
sensingfilamentSchangesduetowidelydifferentthermalconductivityof
samplecomponentthanthecarriergas,asaresultresistanceofSalsovaries
andbridgebecomeunbalanced.Thisoff-balancecurrentissignalledto
recorderwhichdrawstheelutioncurveforchromatographicseparation.

18. whetstone bridge

19. 2.FlameIonizationDetector(FID)
Principle:Theionizationdetectorarebasedontheelectricalconductivity
ofgases.
Atnormaltemperatureandpressuregasesactasinsulatorbutbecome
conductiveofionsifelectronsarepresent.Ifthisconditionaresuchthat
thegasmoleculethemselvesdonotionise,butchangeinconductivitydue
topresenceofaverysmallnumberofionscanbedetected.
ConstructionandWorking:Hydrogengasisaddedwithacapillaryjetif
itwasnotusedasacarriergas,thesamplecomponentsfromeffluent
areburninair(oroxygen,hydrogen)andionized.
Theseionsraiseupwardsandareattractedtowardsanodeorcathode
basedonchargeonthem.
Whentheyimpingeontheelectrodes,currentispassedwhichisrecorded.
Thestrengthandintensityofcurrentdependsonthesampleits
concentration

20. FlameIonizationDetector (FID)

21. 3. Electron Capture Detector (ECD)
Principle
Theelectronaffinityofdifferentsubstancescanbeusedasbasis
forionizationdetectorcalledasElectroncapturedetector(ECD)
Thisdetectordependtoonlythosecompoundswhosemolecule
haveanaffinityforelectronse.g.chlorinatedcompounds,alkyl,
leadetc.
Constructionandworking
ECDconsistofchamberinwhichmetalfoilcoatedwithatritium
(radioactiveβemitter)isusedassteadysourceofslowelectrons.
TheECDismostfrequentlyusedfordetectionandmeasurement
oftraceenvironmentalpollutants.
Ithashighsensitivityforhalogenatedcompoundsthereforeused
fordetectionofherbicidespesticides,tracesinfuelgases,
organometalliccompoundsetc.

22. Electron Capture Detector (ECD)

23. 4.Argonionizationdetector;
Thesedetectorsaresimilartoflameionizationdetectors
withonlydifferencethatargoniongasisusedtoionizethe
samplemolecules.
Theargonionareobtainedbyreactingargongaswith
radioactiveelements.Onceargonionizestheytrytoget
backtostablestatebyeithertakingorgivingelectronfrom
thesamplecomponentsthusmakingsamplemoleculesto
ionsfordetection.

24. SummaryofcommonGC detectors
Detector Type
Flameionization(FID) Mass flow
Support gases Selectivity Detectability Dynamicrange
Hydrogenand air Mostorganiccpds.100 pg 10
7
Thermalconductivity
(TCD)
Concentration Reference Universal 1 ng 10
7
Electron capture(ECD)Concentration Make-up
Halides, nitrates,
nitriles, peroxides,
anhydrides,
organometallics
50 fg 10
5
Nitrogen-phosphorusMass flow Hydrogenand air Nitrogen, phosphorus10 pg 10
6
Flame photometric
(FPD)
Mass flow
Hydrogen and air
possibly oxygen
Sulphur, phosphorus,
tin, boron, arsenic,
germanium, selenium,
chromium
100 pg 10
3
Photo-ionization (PID) Concentration Make-up
Aliphatics, aromatics,
ketones, esters,
aldehydes, amines,
heterocyclics,
organosulphurs, some
organometallics
2 pg 10
7

25. 6.TemperatureProgrammingSystem
Astemperatureprogrammingfacilitatescontrolledincreaseof
eventemperatureduringanalysis.Sothatpeaksofanalytes
shouldbesharpandemergequickly.
Becauseoftemperatureprogrammingfacilitythecomponents
ofwideboilingpointrangemixturemayberesolvedefficiently.
Temperatureprogrammingmaybecarriedoutbythreedifferent
modes
Naturalorballastic
Linear
Matrixormultilinear

26. *ApplicationofGasChromatography
*QualitativeAnalysis:-ofindividualcomponentsofamixture
maybeobtainedbyeitherofthefollowing.
*bycomparingtheretentiontimeorvolumeofthesampletothe
standard,or
*bycollectingtheindividualcomponentsastheyemergefromthe
chromatographandsubsequentlyidentifyingthesecompoundsby
othermethod
*QuantitativeAnalysis-areaunderasinglecomponentelution
peakisproportionaltothequantityofthedetectedcomponent.

27. MiscellaneousapplicationsofGC
Thedetectionofsteroiddrugsusedbyathletesinsportcompetition
andsteroidadministrationtoanimalsintracesbeingcarriedbyGLC.
Inanalysisoffood,theseparationofandidentificationoflipids,
proteins,carbohydrates,flavors,colorantsandtexturemodifiersas
wellasvitamins,steroids,drugsandpesticidestraceelementsbeing
analyzedbyGC.
ItispossibletoanalyzeddairyproductsbyGLCforaldehydeand
ketones(forrancidity),fattyacidandmilksugar.
butterisanalyzedforthebutterfatcontentandforaddedcolorand
flavour.
ItispossibletousepyrolysisGCforseparationofandidentification
ofvolatilemateriallikeplastics,naturalandsyntheticpolymer,paints
andmicrobiologicalsamples.
Itmaybeuseforanalysisofpollutant,inorganiccompoundsetc.

28. Thank You !