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Gas Chromatograph Gas Chromatography - Page Not Found

Gas ChromatographyChromatography: Separate analytes in a mixturewith a resolution in the shortest amount oftime and detection of separated Chromatograph123456= Gas supplies usually have traps to remove anywater, oxygen, hydrocarbons or other contaminants from compressed gases Instruments can have multiple injectors,detectors or columns Injectors and detectors temperatures controlled The GC oven has a large fan and a vent door forrapid cooling/heating. Data collection /and integration system The analyte (GC) necessarily in gas between the mobile phase (carriergas) and the liquid stationary phase(predominant) inside capillary column or onparticles inside a packed column Some packed-column GC uses non-coatedsolid stationary phases; gas-solid adsorptionchromatographyAchieve separation by using suitable; columns with properstationary phase, diameter ofcolumn,stationary phase loading, , and columnlength.

Gas Chromatography Chromatography: Separate analytes in a mixture with a resolution ≥1.5 in the shortest amount of time and detection of separated components.

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  Chromatography, Chromatograph, Chromatography chromatography, Gas chromatograph gas chromatography

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Transcription of Gas Chromatograph Gas Chromatography - Page Not Found

1 Gas ChromatographyChromatography: Separate analytes in a mixturewith a resolution in the shortest amount oftime and detection of separated Chromatograph123456= Gas supplies usually have traps to remove anywater, oxygen, hydrocarbons or other contaminants from compressed gases Instruments can have multiple injectors,detectors or columns Injectors and detectors temperatures controlled The GC oven has a large fan and a vent door forrapid cooling/heating. Data collection /and integration system The analyte (GC) necessarily in gas between the mobile phase (carriergas) and the liquid stationary phase(predominant) inside capillary column or onparticles inside a packed column Some packed-column GC uses non-coatedsolid stationary phases; gas-solid adsorptionchromatographyAchieve separation by using suitable; columns with properstationary phase, diameter ofcolumn,stationary phase loading, , and columnlength.

2 Injection modes to optimize the of loading andseparation of the sample mixture temperature (or pressure) programs for thecolumn detector that is suitable for theanalyte(s)of interestEarly practice of gas Chromatography was done withpacked columns. Such columns are still used forpreparative Chromatography as they can handle largeramounts of (analytical) is practiced with capillarycolumns, which are open tubular Phase: Bonded; poly(50% n-octyl/50%methylsiloxane)Temp. Limits:-60 C to 280 C (isothermal orprogrammed);< mm Tubular ColumnsWCOT, is coated as a specifically is the primary type of capillaryGC column for quantitative analysis:Higher resolution and shorter analysis time and allowsgreater ability to discriminate between is small,is of less concern for analyticalpurposes as long as sufficient analyte is available fordetection; pg/mL (ppt) to g/mL (ppb).

3 Column constructed of fused silica tubing Polyamide coating gives it strength Liquid stationaryphases coated or chemicallybonded to the inner wall of capillary Column , length 30-60mStationary phases substitutedpolysiloxanesOHSiOSiOSiOSiOSi OHRRRRRRRRRRC olumn:Characterized byStationaryphase(mobile phase, LC)materials inert particle loadingwhichis proportional to film thicknessdfand thecolumn range of operation (GC); dependent,Bonded thermally phase-carrier gas (GC), usually an inert gas,primarily pushes the material through the column. InLC; is a solvent, should be compatible with theanalytes and influences the equilibration processin partitioning column suitability for analysis is determined in LC and, in GC:Use with similar polar characteristics as theanalytes to effect a analytes require polar stationary phases to beretained in analytes require less/non-polar generally are a mixture of polar and non-polar components compromise vs.

4 ResolutionDiameter vs. resolutionStationary phase thickness vs. resolutionThick films: increases column bleedingSample capacity v. resolutionSample capacity:the amount of sample that can beinjected onto a column without overloading. Oftenexpressed as grams of sample per gram of is defined as the point at which thesample mass injected makes the column efficiencyN, decrease by 10% from its normal value;sometimes called sample columnsIncreased length leads to longer separation times;band broadening problems arise if too phase thickness and column diameterincreases leads to increased sample capacity andcan provide increased resolution; tradeoffs-longeranalysis time and more column stationary phases bleed more-contaminateMS detection ColumnsThey have greater sample capacity vs.

5 Open tubularcolumns but generates broader peaks, longer retentiontimes and lower for preparative work. Capillary Columns: Higher R Smaller H; high N fast Greater sensitivity analytical Smaller samplecapacity Higher cost/column Columns fragile Packed Columns Low R Larger R, low N Slow Greater samplecapacity Lower cost More rugged preparativeCapillary vs. Packed ColumnsColumn selection GC:Select a stationary phase that would retain( dissolve ) the analytes of phase polarity ~ analyte polarity;(like dissolves like).Selectivity to individual analytes determinesthe quality of separation (ability to discern thecomponents) measured in terms of relative B Order of elution(GC):Lesser retained analytes elute similar molecular characteristics, morevolatile analytes ( , high vapor pressure) elutesearlier; molecular masses elutes polarity, molecular mass, pressureof analytesin concert withthe polarity of thephase(s)to determine the order of Forces (attractive):IMFsdetermine the retention times.

6 GC both phases. This is a forces (weakest but always present)sp nonpolar;Polydimethylsiloxanesp strongly polarPolyethylene glycolsp-nonpolarsp strongly polarGiven similar molecular characteristics,more volatile analytes ( , high vaporpressure) elutes earlier; low molecularmasses elutes times changes with the polarity of thestationary phase (GC in particular).Kovat sRetention Index:A logarithmic scale that relates the corrected retentiontimetr , of an analyte to those oflinearalkanesin agiven column ( )Linearalkanes(or any homologous series) elutes inthe increasing order of their molecular sRetention index (RI)bydefinition foranalkane=100n, where n = # C plot oflog(tr )vsRI is value linear homologues.

7 ''log( )'' log( )rrta b RIRIabt For an analyte eluting from a column (injected withlinear homologues) between the smaller homologue (n)and N larger homologue (N carbons) has an RI of;'','',,log( ) log()100()log() log()rr nr Nr nttRIInN ntt RI indicates the appearance of a given analyte in thechromatogram in relation to straight chain min'','',,log( ) log()100()log() log() 8 (9 8) nr Nr nttRIInN nttI n like an (hypothetical)alkanewith C stationary phases (GC) give different RIvalues for the same analyte because differentstationary phases will have , in any column order of elution of ahomologous series is the same, elutesfirst.

8 Column (stationary phase) characterization:Based on polarity (operationalIMFs) of the stat. of a stationary phaseis expressed withRIsofprobe/index compoundsin of of probe compounds are measuredon ofinterestandon a totally non polar phase squalene(IMFs-dispersion forces only).Forprobe/indexcompound: (Risp RIsqualene) =McReynold sConstant is compoundMeasures IMF oftypeBenzeneAromatic,olefinic;x 1-butanolElectron attractor;y 2-pentanoneElectronrepeller;z 1-nitropropaneNitro,nitrile;u PyridinePyridine;s McReynold sConstantfor probe compound:= I=(RIsp RIsqualene)McReynold sconstant measures the retention of aprobe in , over that insqualene.

9 It is ameasure of a specific type of polarity of sconstant measures the ability to retardanalytes of specific polar characteristics on thestationary compounds and what they measure: polarity arises from the intermolecular forcescertain chemical moieties are capable of exerting.(hand out)My web pagex y z u s Example;x = Ibenzene=(RIsp RIsqualene)benzeneTotal (effective) retardation polarity of stationaryphase:'' .. 'iIxys Average polarity of ;,11005iRii squaleneIPI Index compoundMeasuresIMFsBenzene, x Aromatic,olefinic1-butanol, y Electron attractor2-pentanone, z Electronrepeller1-nitropropane, u Nitro,nitrilePyridine, s pyridineUtility ofMcReynold sConstants-Examples:Alcohol + ether; very similar boiling points.

10 Columnto elute alcohol before ether?z (ether); y (alcohol).SP2401 or OV210 Ether before alcohol?OV275 or SP2340 Benzene,cyclohexane; boiling points-very time frameOV275 Too longAlmost every column in the short list is technicallyUsable here. Consider elution C8 and C18 columns the stationary phase is a thinfilm of non-polar liquid phase (mono molecular layer)that has been chemically anchored to an inert material(Silica particles).Chemically linked to the silica particles surface byreaction with the polar silanol groups on the stationaryphase surface and renders them less polar or columns have silica particles attached to C8carbon units while C18 is coated with C18 columns are more Columns(HPLC)Modes of Separation.


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