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 -3 A)m.p.(gas) - s.p. 1)s.p.: solid （ using adsorption ） ex: SiO 2 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) t r c)Sample capacity
b.p. 22.1 Gas Chromatography -4 ex
22.1 Gas Chromatography -5 B) 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 : H 2, O 2, N 2, CO 2, CH 4. (Fig. 22-5)
22.1 Gas Chromatography -8 packed column vs. open tubular column higher resolution lower sample capacity
22.1 Gas Chromatography -9 3.Temperature programming temp of column v.p. solute, t r sharpens peaks isothermal : constant temp. temp. programming (gradient) : raise the column temp. during the separation.
22.1 Gas Chromatography -10
4.Carrier Gas 22.1 Gas Chromatography -11
22.1 Gas Chromatography 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 Sample injection-2 : 4) operation a).on-column injection (50 ℃ ) -best for quantitative analysis -thermally sensitive compounds -low resolution
22.1 Gas Chromatography -14 b) split injection (350 ℃ ) (only % sample) - concentrated sample - high resolution - dirty samples -could cause thermal decomposition c) splitless injection (220 ℃ ) (80%) - dilute sample - high resolution -solvent trapping (T solvent < 40 ℃ ) -cold trapping (T solute < 150 ℃ )
22.1 Gas Chromatography 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 : adsorption : silica (SiO 2 xH 2 O), alumina (Al 2 O 3 xH 2 O), molecular exclusion, ion-exchange, affinity
22.2 Liquid Chromatography -2 compete with ▲ for binding on s.p. the more strongly bind to s.p. eluent strength
22.2 Liquid Chromatography Eluent strength : Table 22.2 The more polar solvent eluent strength t r 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) 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) 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 isomers D- & L-amino acids
22.3 High-Performance Liquid Chromatography (HPLC) -7 d) Optical isomers separation for ant-inflammatory drug Naproxen
4. Column a)Guard column b)Injection valve 22.3 High-Performance Liquid Chromatography (HPLC) -8
22.3 High-Performance Liquid Chromatography (HPLC) 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 : KH 2 PO 4 (aq) B: CH 3 CN (l)
22.3 High-Performance Liquid Chromatography (HPLC)-11 Reversed-phase column : eluent strength , solvent polarity , t r
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.