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Chapter 22. GC & LC. 22.1 Gas Chromatography. Schematic diagram. 22.1 Gas Chromatography. Columns : open tubular columns. 22.1 Gas Chromatography. m.p.(gas) - s.p. s.p.: solid ( using adsorption ) ex: SiO 2 column ages: Si-O-H cause tailing peak.

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chapter 22

Chapter 22

GC & LC

22 1 gas chromatography
22.1 Gas Chromatography
  • Schematic diagram
22 1 gas chromatography3
22.1 Gas Chromatography
  • Columns : open tubular columns
22 1 gas chromatography4
22.1 Gas Chromatography
  • m.p.(gas) - s.p.
    • s.p.: solid(using adsorption)ex: SiO2

column ages: Si-O-H cause tailing peak.

2) s.p.: liquid(GLC, using partition)

a range of polarities (Table 22-1), “like dissolves like”

Decrease thickness of stationary phase leads to

      • Resolution (H)
      • tr
      • Sample capacity
22 1 gas chromatography6
22.1 Gas Chromatography

Like dissolves like (a) S.P: nonpolar, b.p. dependent (b) S.P: polar

B) The effects of column polarity on separation

slide7

How changing the S.P. can affect separation

Figure 22-4 Resolution of trans fatty acids in hydrogenated food oil improves when the stationary phase is changed from DB-23 to HP-88 (aryl group)

P.484

22 1 gas chromatography8
22.1 Gas Chromatography

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 : inorganic materials with nanometer-size cavities that retain & separate small molecules : H2, O2, N2, CO2, CH4. (Fig. 22-5)

c) Guard column

Collect nonvolatile components that would otherwise be injected into a column and never be eluted.

22 1 gas chromatography9
22.1 Gas Chromatography

packed column vs. open tubular column

higher resolution

lower sample capacity

22 1 gas chromatography10
22.1 Gas Chromatography
  • Temperature programming

 temp of column  v.p. solute,

 tr

 sharpens peaks

isothermal :constant temp.

temp. programming (gradient) :

raise the column temp. during the separation.

22 1 gas chromatography 9
22.1 Gas Chromatography -9

Figure 22-6 (a) Isothermal and (b) programmed temperature chromatography of linear alkanes through a packed column with a nonpolar stationary phase.

slide13

22.1 Gas Chromatography

  • 5. Sample Injection
      • 1) gasses, liquids, or solids
      •  vaporized, not decomposition
      • 2) injection time   bands broader
      • 3) injected by syringe (manual or automatic injection)
slide14

22.1 Gas Chromatography

Figure 22-7 Injection port operation for (a) split, (b) splitless, and (c) on-column injection into an open tubular column.

22 1 gas chromatography15
22.1 Gas Chromatography

split injection (350℃) (only 0.1-10% sample)

Routine method

concentrated sample

high resolution

dirty samples

could cause thermal decomposition

splitless injection (220℃) (80%)

For quantitative analysis and for analysis of trace components of mixture

high resolution

solvent trapping (Tsolvent < 40℃) for dilute sample

cold trapping (Tsolute < 150℃) for high-boiling solutes

on-column injection(50℃) (100%)

best for thermally unstable solutes.

22 1 gas chromatography16
22.1 Gas Chromatography

5. Detectors

Qualitative analysis :mass spectrometer, IR

Quantitative analysis :area of a chromatographic peak.

22 1 gas chromatography17
22.1 Gas Chromatography

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)

c) Electron capture detector :

-for compounds containing atoms with high electron affinities.

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

22 1 gas chromatography19
22.1 Gas Chromatography

d) Mass Spectrometric Detection and Selected Reaction Monitoring :

- A mass spectrometer is the single most versatile detector.

- Total Ion Chromatogram (TIC)

- selected ion monitoring (SIM) at on value of m/z

- selected reaction monitoring (SRM) = tandem mass =

MS/MS

- Multiple reaction monitoring (MRM)

slide20

QQQ Mass Spectrometer

Precursor ion (parent ion) vs. Product ions (daughter ion)

Solid phase extraction (SPE)

22 2 liquid chromatography
22.2 Liquid Chromatography

1. open, gravity-feed column

2. closed column (under high pressure) packed with micron-size particles. (HPLC)

3. stationary phase :

a. adsorption : silica (SiO2xH2O), alumina (Al2O3xH2O),

b. molecular exclusion,

c. ion-exchange, affinity

22 2 liquid chromatography24
22.2 Liquid Chromatography

compete with▲for binding on s.p.

the more strongly bind to s.p.eluent strength 

22 2 liquid chromatography25
22.2 Liquid Chromatography

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.

slide28

22.3 High-Performance Liquid Chromatography (HPLC)

1. Through a closed column, and needs high pressure.

2. s.p. particles size 

microporous particles of silica

with diameters of 1.5-10 um

s.p.  m.p. faster,

i.e. C in van Deemter eqn.

 resolution 

22 3 hplc30
22.3 HPLC

3. 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 hplc31
22.3 HPLC

c) Bonded stationary phase.

polar vs. nonpolar

d) Optical isomers

D- & L-amino acids

for drug industry

see p.494 for R = polar or nonpolar

22 3 hplc32
22.3 HPLC

d) Optical isomers separation

ex: for ant-inflammatory drug Naproxen

slide33

22.3 HPLC

  • 4. Column
      • Guard column
      • Injection valve
22 3 hplc34
22.3 HPLC

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 hplc35
22.3 HPLC
  • Figure 22-20 Isocratic HPLC
  • separation of a mixture of aromatic
  • compounds at 1.0 mL/min on a
  • 0.46×25 cm Hypersil ODS column
  • (C18 on 5-μm silica) at ambient
  • temperature (~22℃):
  • benzyl alcohol;
  • phenol;
  • 3’, 4’-dimethoxyacetopheneone;
  • benzoin;
  • ethyl benzoate;
  • toluene;
  • 2,6-dimethoxytoluene;
  • o-methoxybiphenyl.

A : KH2PO4(aq)

B: CH3CN(l)

22 3 hplc36
22.3 HPLC

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

slide37

Detectors

- Ultraviolet detector

- Electrochemical detector

redox reaction

- Fluorescence detector

LC-MS

- ESI (Electrospray ionization)

- APCI (atmospheric pressure chemical ionization)

slide38

Figure 22-23 Atmospheric pressure chemical ionization interface between liquid chromatography column and mass spectrometer.

P.500