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

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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