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University of Guilan 12/19/2015
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Column’s effects in Separation
University of GuilanStudent: Babak Bozorgi
Date 14 / 12/ 1393
Under supervision of : Dr. Ali Mohammadkhah
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Scheme Of A Universal Gas Chromatograph
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Column Type
Column
Packed
Capillary
0.25mm
Column
Wide Bore
Medium Bore
Narrow Bore 0.15mm
0.32mm
0.53mm
1/8 inch
1/4 inch
1/16 inch
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Separation Process
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Separation Process
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How Separation Occurs
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Peak Asymmetry
Retained & Unretained Component
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L (cm)t0 (sec)
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Recommended Unretained Compounds
DETECTOR COMPOUND
FID Methane, Propane, Butane
TCD Air, Methane, Butane
ECD Methylene Chloride Vapor
NPD Acetonitrile Vapor
FPD Hydrogen Sulfide
MS Air, Methane, Propane, Argon
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Retention Factor
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Selectivity
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Number of Theoretical Plates (N) and Height Equivalent to a Theoretical Plate (H)
- Number of theoretical platesParameter indicating column efficiencyThe larger the value, the more efficient the
column.
- Height Equivalent to a Theoretical Plate (HETP)Parameter indicating column efficiency(Independent of column length)The smaller value, the more efficient the column
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Theoretical plate number Nth
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L: Column length (cm or mm)
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Theoretical plate number Nth
Nth=5.545[tr/W1/2]2
Nth=16[tr/Wb]2
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Height Equivalent to a Theoretical Plate
HETP= L/NthHETP : Height Equivalent to a Theoretical Plate
L : Column Length
Nth: Theoretical plate Number
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Peak width as a function of HETP
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Retention vs. Efficiency
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Retention vs. Selectivity
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Selectivity vs. Efficiency
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Van DeemterEquation
Golay Equation
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Resolution & SeparationIf Rs 1.25 no Baseline SeparationIf 1.25 Rs 1.5 Separation depends on peak SymmetryIf Rs 1.5 Baseline Separation
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H = A + B/u + C.uH :HETP (Plate Height)
A : Eddy Diffusion Term
B : Longitudinal Diffusion Term
u : Linear Gas VelocityC : Resistance to Mass Transfer Coefficient
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Eddy Diffusion Term
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Van Deemter Equation In the Case of a Packed Column
A=2dp Diffusion of eddies by multiple pathwaysdp: Diameter of column packing particles: Packing irregularity constant
H: HETP (Height Equivalent to a Theoretical Plate)
u: Linear velocity of carrier gas
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Longitudinal Diffusion Term
B=2Dg Molecular diffusion in gas phase
Linear Velocity Mobil Phase : Coefficient for
irregularity in carrier gas flow line
Dg: Diffusion coefficient for solute molecules in gas phase
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H: HETP (Height Equivalent to a Theoretical Plate)
u: Linear velocity of carrier gas
Van Deemter Equation In the Case of a Packed Column
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B: 2DgDg: Diffusion coefficient for solute molecules in gas phase
Golay Equation In the case of a Capillary column
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Resistance to Mass Transfer Cs Term
Capacity Ratio Amount of Stationary
Phase Particle Size
Diffusion Coefficient in Stationary PhaseTemperature
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Resistance against mass transfer in Stationary Phase
k: Capacity Ratio
df: Film thickness of stationary phase
Dl: Diffusion coefficient for solute molecules in liquid phase
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Resistance to Mass Transfer Cm Term
Particle Size Linear Velocity Mobil
Phase Diffusion Coefficient in
Mobile Phase Porosity Viscosity Of Mobile
Phase Temperature
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Resistance against mass transfer in Mobile phase
k: Capacity ratio r: Internal diameter of capillary column
Dg: Diffusion coefficient for solute molecules in Gas phase
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<<<To reduce HETP>>>
Reduce IDuse column with smaller diameter
Reduce dfreduce film thickness
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Efficiency of Packed vs. Capillary Column
Column Type Dimension Nth optimum Nth practical
Packed 2 m 2.1 mm ID 8000 4500
Capillary 10 m 0.53 mm ID 13000 8000
10 m 0.32 mm ID 32000 25000
10 m 0.25 mm ID 50000 35000
10 m 0.10 mm ID 100000 65000
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Compare between Packed and Capillary Column
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Influence of Film Thickness on H-u
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Influence of Column ID on H-u
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Efficiency of separation Columns
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Column Diameter vs. Peak Height AND Analysis time
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Maximum Plate Number and Plate Number per meter
D N max N/meter L
mm m
Packed 0.53 12000 3000 4
Wide Bore 0.53 320000 1600 200
Medium Bore 0.32 300000 3000 100
Narrow Bore0.25 225000 4500 50
0.15 200000 8000 25
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Plate Number vs. Column Length
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Speed Packed vs. Capillary Column
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Advantages Of narrow-bore Columns
High efficiencyInfluence of diameter
on separation
High SpeedInfluence of diameter
on analysis time
50 m × 0.53 mm 100.000 Plates25 m × 0.25 mm 100.000 Plates15 m × 0.15 mm 100.000 Plates10 m × 0.10 mm 100.000 Plates
50 m × 0.53 mm 300 second25 m × 0.25 mm 120 second15 m × 0.15 mm 70 second10 m × 0.10 mm 40 second
Source : Chrompack
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Disadvantages Of narrow-bore Columns
Low sample Capacity(Limited Working range)
Low flow(dead volume Problem)
Special hardware required
Influence of Diameteron sample capacity
Influence of Diameteron flow rate (e. g. for H2)
ID (mm) Sample Capacity (ng)
ID (mm) Flow rate(ml/min)
Special injection techniques (narrow start peak width)0.10 5 – 10 0.10 0.2
0.18 10 – 20 0.18 0.6
0.25 50 – 100 0.25 1.4 Optimized detectors (renaissance of the
TCD0.32 400 – 500 0.32 2.0
0.53 1000 - 2000 0.53 5.2
Source : Restek
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HETP vs. Velocity
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Analysis time as a function of Column ID
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Resolution
Effect Of K’ On Resolution
Before After IncreaseRs (%)k´ k´/(k´+1) k´ k´/(k´+1)
0.1 0.09 0.2 0.17 89
0.2 0.17 0.4 0.27 71
0.4 0.29 0.8 0.44 52
0.7 0.41 1.4 0.58 41
1.5 0.60 3.0 0.75 25
5.0 0.83 10.0 0.91 10
10.0 0.91 20.0 0.95 4
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Contribution of Nth , , K’On Resolution
Optimization Parameters
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Increase Capacity Speedk' α Nth
Resolution
length - -
I.D. -
Amount Of Stationary Phase
-
Temperature
Start Chromatogram end
u - - -
Optimum
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Optimization Targets
Quick Reference For Packed ColumnInside Diameter
(mm)Nitrogen (ml/min) Helium/Hydrogen
(ml/min)
2 8-15 15-30
3 15-30 30-60
4 30-60 60-100
Separation Speed
Flow 0/- +
Length + -
Temperature 0/- +
Loading 0/+ +
Mesh size (Particle Size) + 0
I.D. - 0
Influence Of Increasing several parameters
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Quick Reference For Capillary Column
Carrier Gas
IDmm
UCm/s
Flowml/min
Recommended Inlet Pressure
WCOT Columns Bar/25m
PLOT ColumnBar/25m
N2
0.150.250.320.530.53
15-2010-157-11
4-8 opt30-40 adv
± 0.2± 0.4± 0.5± 1.0± 5.0
1 – 1.30.4 – 0.50.2 – 0.250.05 – 0.080.35 – 0.4
--------
0.5-0.80.1-0.30.5-0.7
He
0.150.250.320.530.53
35-4022-2716-21
11-16 opt60-70 adv
± 0.4± 0.7± 0.9± 2.0± 9.0
2-2.50.7-0.90.4-0.50.1-0.150.6-0.7
--------
0.7-1.00.3-0.50.8-1.0
H2
0.150.250.320.530.53
50-6040-4529-34
20-25 opt70-80 adv
± 0.6 ± 1.0± 1.4± 3.0± 12.0
2-2.50.7-0.90.4-0.50.1-0.150.4-0.5
--------
0.6-0.80.2-0.30.6-0.8