Chapter 22

GC & LC

22.1 Gas Chromatography -1

1. Schematic diagram

22.1 Gas Chromatography -2

2. Columns : open tubular columns

22.1 Gas Chromatography -3A) m.p.(gas) - s.p.

1) s.p.: solid（ using adsorption） ex: SiO2

column ages: Si-O-H cause tailing peak.2) s.p.: liquid（ GLC, using partition） Table 22-1

Decrease thickness of stationary phase leads to

a) Resolution (H)b) tr c) Sample capacity

b.p.

22.1 Gas Chromatography -4

ex

22.1 Gas Chromatography -5B) The effects of column polarity on separation

Like dissolves like

(a)S.P: nonpolar

b.p. dependent

22.1 Gas Chromatography -6

-one:C=O

-ol: OH

S.P. : Polar

22.1 Gas Chromatography -7

C) Common solid s.p. :

a) Porous carbon : larger molecules bind more tightly than small ones, flexible molecules bind more than rigid ones

b) Molecular sieves : retain & separate small molecules : H2, O2, N2, CO2, CH4. (Fig. 22-5)

22.1 Gas Chromatography -8packed column vs. open tubular column

higher resolutionlower sample capacity

22.1 Gas Chromatography -9

3. Temperature programming

temp of column v.p. solute,

tr

sharpens peaksisothermal : constant temp.temp. programming (gradient) : raise the column temp. during the sepa

ration.

22.1 Gas Chromatography -10

4. Carrier Gas

22.1 Gas Chromatography -11

22.1 Gas Chromatography -12

5. Sample Injection-1

1) gasses, liquids, or solids

vaporized, not decomposition

2) injection time bands broader

3) injected by syringe (manual or automatic injection)

22.1 Gas Chromatography -12

22.1 Gas Chromatography -13

5. Sample injection-2 :

4) operation

a).on-column injection (50 )℃- best for quantitative analysis- thermally sensitive compounds- low resolution

22.1 Gas Chromatography -14b) split injection (350℃) (only 0.1-10% sample)

- concentrated sample

- high resolution

- dirty samples- could cause thermal decomposition

c) splitless injection (220℃) (80%)

- dilute sample

- high resolution

- solvent trapping (Tsolvent < 40℃)- cold trapping (Tsolute < 150℃)

22.1 Gas Chromatography -15

5. Detectors

Qualitative analysis :mass spectrometer, IR

Quantitative analysis :area of a chromatographic peak.

22.1 Gas Chromatography -16

a) Thermal conductivity detector:

-most general way

-responds to everything

-not sensitive enough for high resolution.

b) Flame ionization detector :

-most popular

-mainly responds hydrocarbons (C-H)

22.1 Gas Chromatography -17

c) Electron capture detector :

- for compounds containing atoms with high electron affinities.

- sensitive for halogen, C=O, NOx, & orgaometallic compounds.

d) Other detectors : p 476

22.2 Liquid Chromatography -1

1. open, gravity-feed column 2. closed column (under high pressure)

packed with micron-size particles. (HPLC)

3. stationary phase :

① adsorption : silica (SiO2xH2O), alumina (Al2O3xH2O),

② molecular exclusion, ③ ion-exchange, affinity

22.2 Liquid Chromatography -2compete with ▲ for binding on s.p.

the more strongly bind to s.p.eluent strength

22.2 Liquid Chromatography -3

4. Eluent strength : Table 22.2

The more polar solvent

eluent strength

tr

5. Gradient elution : increased the eluent strength during the separation in liquid chromatography.

22.3 High-Performance Liquid Chromatography (HPLC) -1

22.3 High-Performance Liquid Chromatography (HPLC) -21. Through a closed column, and needs high

pressure.

2. s.p. particles size (s.p. m.p. faster,

i.e. C in van Deemter eqn.)

resolution

22.3 High-Performance Liquid Chromatography (HPLC) -3

22.3 High-Performance Liquid Chromatography (HPLC) -4

22.3 High-Performance Liquid Chromatography (HPLC) -53. Stationary phase

a) Normal-phase chromatography : polar s.p. and less polar solvent. Eluent strength is increased by adding a more polar solvent.

b) Reversed-phase chromatography : low-polarity s.p. and polar solvent. Eluent strength is increased by adding a less polar solvent.

22.3 High-Performance Liquid Chromatography (HPLC) -6

c) Bonded stationary phase. polar vs. nonpolar p.461

d) Optical isomersD- & L-amino acids

22.3 High-Performance Liquid Chromatography (HPLC) -7

d) Optical isomers separation for ant-inflammatory drug Naproxen

4. Columna) Guard columnb) Injection valve

22.3 High-Performance Liquid Chromatography (HPLC) -8

22.3 High-Performance Liquid Chromatography (HPLC) -9

5. Solvents a) Isocratic elution :

elution with single solvent or a constant solvent mixture

b) Gradient elution : solvent is changed continuously from a weak eluent strength to a strong eluent strength by mixing more and more of a strong solvent to a weak solvent during the chromatography.

22.3 High-Performance Liquid Chromatography (HPLC) -10

A : KH2PO4(aq)

B: CH3CN(l)

22.3 High-Performance Liquid Chromatography (HPLC)-11

Reversed-phase column :eluent strength , solvent polarity , tr

22.3 High-Performance Liquid Chromatography (HPLC)-12

The gradient can be used to resolve all peaks by reducing the time from 2 h to 38 min.