Chromatography

Gas

GSC GLC

Liquid

LSC LLC IEC GPC AC

Gas Chromatography

Mobile phase ：gas (usually He, N2, H2)

Stationary phase ：non-volatile liquid or solid particles

Analytes for GCHave a significant vapor pressureThermal stable

ex ： gas, most non-ionized small and medium (C25) organic molecules, many organometallic compounds.

Not for organic and inorganic salts, macromolecules

樣品形式： solid, liquid, gas

injectionport

exit

detector

septum

carrier gasin

column oven

column

computer orrecorder

detectoroven

injectoroven

Schematic diagram of a gas chromatography

Carrier gas

no reactivenon flammablenon-toxic

N2, He, H2

H

μAB

C

CBAH

N2→packed columnHe, H2→open tube column

N2

He

H2

Pla

te h

eigh

t (m

m)

Linear velocity (cm/s)

H2 and He both give optimal resolution at higher flow rates than N2

Column

flow0.1 ~ 0.53 mminner diameter

stationary phase(0.1 ~ 5μm thick)

outer wall of columnOpen tubular columns

Packed columncontain a fine solid support coated with a nonvolatile liquid stationary phase; or the solid itself may be the stationary phase.

Packed column Open tubular column

I.D. 2 ~ 6 mm 0.2 ~ 0.75 mm

L 0.5 ~ 5 m 15 ~ 100 m

Open tubular columns

Compared with packed columns, open tubular

columns offer ：

1. higher resolution

2. shorter analysis time

3. greater sensitivity

4. lower sample capacity

wall-coatedopen tubular column

(WCOT)FSOT: fused-silica, OTC

support-coatedopen tubular column

(SCOT)

porous-layeropen tubular column

(PLOT)

Decreasing thickness of stationary phase leads to1. decreased plate height2. decreased retention time3. decreased capacity for analyte

GSC

separation based on surface adsorption

Absorbent ：Molecular sieves ： for H2, O2, N2, CH4, CO (PLOT)

Charcoal ： for permanent gas C1 ~C4, stack gas (NOx, SOx)

Silica gel, alumina (PLOT)

Porous polymer

GLC

a solid support coated with a liquid stationary phase

Solid support for GLC ：Diatomaceous earths (diatom: single-cell algae)

graphite carbon, charcoal

Teflon

Liquid phase for GLC ：Chemical stable and unreactive toward analyte

Involatile and thermal stable

OHSiCl Si

R

R'

R"

O SiSiR

R'R"

silanol

Separation mechanism

(1) selective solute-S.P. interaction

(2) difference in vapor pressure of solute

S.P. 分類non-polar phase

polar phase

special phase

chiral phase

What is the chiral molecule？

對掌性異構物 (enantiomers):具有相同的物性及化性。Ex: boiling point 、 melting point 、 density 、 refractive indexes 、 ionization 、 reaction properties 。

Mirror

C

OH

CH2OHHOC

H

C

HHO

COHHOH2C

Chiral compound 的重要性

(1) 可運用於製藥、農藥、食物及飲料。(2) 瞭解具有生物活性分子的生物合成及代謝。(3) 使用的分離技術： HPLC 、 GC 、 CE …etc 。

R formS form

鎮靜效果畸胎原 Different biological effect

譬如：

N

O

ONH

O

O

*

thalidomide

莎痢竇邁

對掌固定相 Chiral Stationary Phase(CSP)1.Dalgiesh 1952 three-point interaction2. 暫時性的非對映異構錯合物

transient diastereomeric complex

流動沖堤方向R form

S form

Parameters influence on selectivity

The nature of the S.P.

The conc. of S.P.

Column T • isothermal temp. control

• programming temp. control

The choice & pretreatment of the solid support

Temperature and pressure programmingD

etec

tor

resp

onse C6 C7

C9air C8

Low T

C6 C7 C9

airC8 C10 C11 C12 High T

Det

ecto

r re

spon

se

C6 C7 C9

airC8 C10 C12C11 C13

time

T

Det

ecto

r re

spon

se

Retention index (I)

)(log)(log

)(log)(log)(100

''

''

ntNt

ntunknowntnNnI

rr

rr

n ： # of C atoms in the smaller alkane N ： # of C atoms in the larger alkanetr(n) ： adjusted retention time of smaller alkane tr(N) ： adjusted retention time of larger alkanetr(unknown) ： adjusted retention time of unknown

Retention index relates the retention time of a solute to the retention times of linear alkanes.

C8

Time (min)3.50.25

Det

ecto

rR

espo

nse C7

C9

xair

5.6 7.46.3

Kovats index for linear alkanes equals 100 times the

number of carbon atoms

0.25)-6.5log(0.25)-4.7( log0.25)-6.5log(0.25)-(6.3 log

8)-(9 8100 I

I = 842

Injection conditions for split, splitless, and on-column injection

Syringe for solid-phase microextraction.The fused silica fiber is withdrawn inside the steel needle after sample collection and when the syringe is used to pierce a septum.

Sampling by solid-phase microextraction and desorption of analyte from the coated fiber into a gas chromatography.

Purge and trap apparatus for extracting volatile substances from a liquid or solid by flowing gas.

Detectors

Thermal Conductivity detector

gas

e-

gas

e-

high thermal conductivitymain component entering detector

analyte appears, T.C., Temp , Wire Resistance , detector current “read-out”

Thermal conductivity detector ：104 linear response range

H2 and He give lowest detection limit

sensitivity increase with

increasing filament current

decreasing flow rate

lower detector block temperature

Flame ionization detector (FID)

column effluent

H2

air

cathode(collects CHO+ ions)anode

Carbon atoms (except carbonyl and carboxyl carbons) produce CH radicals, witch are though to produce CHO+ ions in the flame ：

CH + O → CHO+ + e-

Flame ionization detector ：H2 give best detection limit

Signal proportional to number of susceptible carbon atoms

100-fold better detection than thermal conductivity

107 linear response range

Insensitive to non-hydrocarbons

Electron capture detector (ECD)

electrodes

Radioactive-emitter

Ni63 +

+

insulator

-

-

- + gas - + gas+ + e- (standing current)e- + solute solute- (e- capture)solute- + gas+ solute + gas

time

Cur

rent

(I)

standing current

Electron capture detector ：Non-destructive

non-linear

selective to e- capturing solutes

detection limit 5 fg

Other detectorsElectron capture ： halogens, conjugated C=O, -C≡N, -NO2

nitrogen-phosphorus ： highlights P, N

Photoionization ： aromatics, unsaturated compounds

Sulfur chemiluminescence ： S

Nitrogen chemiluminescence ： N

Atomic emission ： most elements (selected individually)

Mass spectrometer ： most analytes

Infrared spectrometer ： most analytes.

Name Type Selective For ： Typical Min. Detectible Level (S/N=2)

Linear Dynamic Range

FID SelectiveMaterials that ionize in air/H2 flame

5 pg C/sec 107

TCD UniversalAnything with thermal cond. Different from carrier

400 pg/ml carrier 106

ECD Selective Gas-phase electrophores0.1 pg Cl/sec(varies w/structure)

104

PID Selective Compounds ionized by UV 2 pg C/sec 107

Thermionic Selective N, P, heteroatoms 0.4 pg N/sec ； 0.2 pg P/sec 104

ELCD Selective Halogens, N, S0.5 pg Cl/sec ； 2 pg S/sec4 pg N/sec

106 ； 104

104

FPD Selective P, S 20 pg S/sec ； 0.9 pg P/sec 103 ； 104

FTIR Universal Molecular vibrations 1000 pg of strong absorber 103

MSD Universal Tunable for any species 10 pg to 10 ng (depending on SIM vs. scan) 105

AED Universal Tunable for any species 0.1 – 20 pg/sec(depending on element) 104