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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.