Gas Chromatography

1. Introduction

2. Stationary phases

3. Retention in Gas-Liquid Chromatography

4. Capillary gas-liquid chromatography

5. Sample preparation and injection

6. Detectors

(Chapter 2 and 3 in The essence of chromatography)

Capillary Gas-Liquid Chromatography

A. Separation efficiency and rate theory

B. Preparation of Capillary Column

C. Evaluation of Capillary Column

capillary

packed

Packed-bed and capillary GC

Capillary GC has much higher separation efficiency than packed-bed GC!

Rate theory-- Van Deemter Equation

(1+εp/εe)2 Dm

u2λ dp + qsk

(1+k)2df

2

Dsu+ +

dp2

Dmf(k) u

1. Packed-bed system

H = A + B/u + (CS + CM)u

λ:column packing factor (0.5~1.5)dp: average size of the filling particlesεp: intraparticle porosityεe: interparticle porosityDm: solute diffusion coefficient in mobile phase. k: capacity factor k = K (Vs/Vm)Ds: solute diffusion coefficient in stationary phase.qs:shape factor for the stationary phase coating coating (2/3 for a thin layer).df: thickness of stationary phase

2. Capillary system—open tubular system

2Dm

u2k

3(1+k)2df

2

Dsu+ d2

Dmu

H = B/u + (CS + CM)u

1+6k+11k2

96(1+k)2+

No eddy diffusion!

Hmin = 2*(BC)1/2

uopt = (B/C)1/2

H = B/u + Cu

d2

Dm

1+6k+11k2

96(1+k)2Cm =

2k3(1+k)2

df2

Ds

d2

Dm

1+6k+11k2

96(1+k)2+CS + CM =

H = B/u + (CS + CM)uThe ratio of CS and Cm contributions to the term of resistance to mass transfer is determined by the phase ration.

(Vm/Vs) = d/4df , when, d>>df

Hmin = 2*(BC)1/2

uopt = (B/C)1/2

The Effect of Carrier Gas

H = B/u + (CS + CM)uDAB =

1.00 x 10-3 T1.75

P[(sum vi)A1/2 + (sum vi)B

1/2] ( )

MWA

1MWB

1

DAB = kT/(6πηBrA)

gas

liquid

2Dm

u2k

3(1+k)2df

2

Dsu+ d2

Dmu

H = B/u + (CS + CM)u

1+6k+11k2

96(1+k)2+

T

u

df

d

k

Parameters affecting plate height

Polymer coatingFused silica tubeCoated stationary phase

Preparation of Capillary Column

1. Materialsa. glass: soda-lime (soft) alkaline

SiO2 67.7%, Na2O 15.6%, CaO 5.7%, MgO 3.9%, Al2O3 2.8%, BaO 0.8%, and K2O 0.6%

borosilicate (hard), acidicSiO2 67.7%, B2O3 13 %, Na2O 3.0%, Al2O3 2.0%, and K2O 1.%

b. fused silicaSiCl4 + O2 SiO2

Surface: Si—OH, O--SiH-O

Silanol Siloxane

2. Film Formation on Inner Surface of Tubes

(A) Uniform stationary film is essential for high-efficiency separation

Thin, smooth, and homogeneous film(1) Surface tension (wettability): the surface tension of stationary

phase should be smaller than that of glass or fused silica.

(2) The stability of the film depends on the viscosity of liquid and thickness of film (surface tension).

(B) Surface modification

(1) Improvement of wettability of glass surface: HCl (gas)(2) Deactivation: silylation

(C) Coating Techniques

Dynamic coating, and Static coating

Evaluation of Column Quality

1. Activity test for uncoated columns

2. Grob test for coated columns

Grob Test

Essence of Chromatography, Page 154

Old column

New column

(1) The height of the peaks(2) The shape of the peaks

3. Columns Thermal Stability

The bleed products from stationary phase consist primarily of low molecular weight impurities. Fused silica columns show very low levels of thermally induced catalytic phase decomposition

Capillary Gas-Liquid Chromatography

A. Separation efficiency and rate theory

B. Preparation of Capillary Column

C. Evaluation of Capillary Column