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Intro to Chromatographic Separations Chap 26. CHROMATOGRAPHY. Originally based on separation and identification by color All have in common: Stationary phase Mobile phase (eluent) Separation based on differences in migration rates of components of a mixture - PowerPoint PPT Presentation
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Intro to Chromatographic SeparationsIntro to Chromatographic Separations
Chap 26Chap 26
• Originally based on separation and identification by Originally based on separation and identification by colorcolor
• All have in common:All have in common:
(a)(a) Stationary phaseStationary phase
(a)(a) Mobile phase (eluent)Mobile phase (eluent)
(a)(a) Separation based on differences in migration Separation based on differences in migration rates of components of a mixturerates of components of a mixture
i.e., The extent of which components are i.e., The extent of which components are partitionedpartitioned between mobile and stationary phasesbetween mobile and stationary phases
AAmobilemobile ⇌⇌ A Astationarystationary
CHROMATOGRAPHYCHROMATOGRAPHY
Quantitative Description of Column EfficiencyQuantitative Description of Column Efficiency► Two related terms used:Two related terms used:
(1)(1) Plate height, HPlate height, H
(2)(2) Number of theoretical plates, NNumber of theoretical plates, N
(3)(3) Related by: Related by: (Eqn. 26-16) (Eqn. 26-16)
► Efficiency increases as NEfficiency increases as N ↑↑ and as Hand as H ↓↓HLN
LH2
2
R
Wt16N
(Eqn. 26-17)(Eqn. 26-17) (Eqn. 26-21)(Eqn. 26-21)
Effect of Particle Size on Plate HeightEffect of Particle Size on Plate HeightFig. 26-11Fig. 26-11
• Smaller particles reduce H and increase resolutionSmaller particles reduce H and increase resolution
Optimization of Column PerformanceOptimization of Column Performance
Objectives:Objectives:
• reduce zone broadeningreduce zone broadening
• alter relative migration rates of solutesalter relative migration rates of solutes
Column ResolutionColumn Resolution (R (RSS) ) ≡ ≡
(Eqn. 26-24)(Eqn. 26-24)
Recall thatRecall that efficiency increases as N and as Hefficiency increases as N and as H
• lengthening column increases Nlengthening column increases N
• lower H by altering flow rate of mobile phase orlower H by altering flow rate of mobile phase or
decreasing particle size of packingdecreasing particle size of packing
BA
ARBR
WWtt
])()[(2R S
ttRR
WW
22σσ
LH2
2
R
Wt16N
(Eqn. 26-17)(Eqn. 26-17) (Eqn. 26-21)(Eqn. 26-21)
Desire RS > 1.50
The General Elution Problem in ChromatographyThe General Elution Problem in ChromatographyFig. 26-15Fig. 26-15
Effect of Solvent Variation on ChromatogramsEffect of Solvent Variation on ChromatogramsFig. 26-14Fig. 26-14
Fig. 26-12Fig. 26-12
The General Elution Problem in ChromatographyThe General Elution Problem in Chromatography
Solution to the General Elution ProblemSolution to the General Elution Problem
• For liquid chromatography (LC):For liquid chromatography (LC):
• vary kvary kAA by varying composition of mobile phase during by varying composition of mobile phase during elution (elution (gradient elutiongradient elution or or solvent programmingsolvent programming))
• For gas chromatography (GC):For gas chromatography (GC):
• use temperature programminguse temperature programming
Result of Temperature ProgrammingResult of Temperature ProgrammingD
etec
tor
Sign
al
Gas ChromatographyGas Chromatography
Chap 27Chap 27
Schematic of a Gas ChromatographSchematic of a Gas ChromatographFig. 27-1Fig. 27-1
A Soap-Bubble FlowmeterA Soap-Bubble FlowmeterFig. 27-2Fig. 27-2
Sample Port and InjectorSample Port and Injector
• Must flash volatize andMust flash volatize and introduce sample onto columnintroduce sample onto column
• Heated ~ 50°C above BP ofHeated ~ 50°C above BP of least volatile compoundleast volatile compound
• May be:May be:
• split (cap columns & GC-MS)split (cap columns & GC-MS)
• splitless (packed columns)splitless (packed columns)
Fig 27-4
Column ConfigurationsColumn Configurations
Two types:Two types:
• Packed columns (L ~ 1 – 5 m)Packed columns (L ~ 1 – 5 m)
• Open Tubular Column (L ~ 1 – 100 m)Open Tubular Column (L ~ 1 – 100 m)
Typical Fused Silica Capillary ColumnTypical Fused Silica Capillary Column
~20 – 100 m~20 – 100 m
Fig. 27-6Fig. 27-6