![Page 1: 1 Gas Chromatography (GC; GLC; GSC) “Basic Gas Chromatography” by McNair, Wiley, 1997 “Modern Practise in GC” by Grob, pp. 900 “Gas Chromatography” by](https://reader035.vdocuments.us/reader035/viewer/2022062407/56649da25503460f94a8f9e2/html5/thumbnails/1.jpg)
1Gas Chromatography (GC; GLC; GSC)“Basic Gas Chromatography” by McNair, Wiley, 1997“Modern Practise in GC” by Grob, pp. 900“Gas Chromatography” by Willett, pp. 250 (Wiley) Martin and Synge
– 1941 idea; 1952 instrument– 1969 Nobel prize
Manufacturers – Perkin Elmer, Hewlett Packard, Shimadsu, Phillips, Carlo
Erba, Varian, etc– price? inexpensive; many per laboratory
Separation technique — pure n’ simple– partitioning between two phases
![Page 2: 1 Gas Chromatography (GC; GLC; GSC) “Basic Gas Chromatography” by McNair, Wiley, 1997 “Modern Practise in GC” by Grob, pp. 900 “Gas Chromatography” by](https://reader035.vdocuments.us/reader035/viewer/2022062407/56649da25503460f94a8f9e2/html5/thumbnails/2.jpg)
2Schematic GC apparatus Liquid sample of
ca. 0.1l volume injected via a syringe into heated injector port where it is rapidly volatilised and swept by a stream of flowing (carrier) gas thru a column & out via a detector.
D SI GNALI NJECT OR PORT
COLUMNOVEN
CARRI ERGAS
![Page 3: 1 Gas Chromatography (GC; GLC; GSC) “Basic Gas Chromatography” by McNair, Wiley, 1997 “Modern Practise in GC” by Grob, pp. 900 “Gas Chromatography” by](https://reader035.vdocuments.us/reader035/viewer/2022062407/56649da25503460f94a8f9e2/html5/thumbnails/3.jpg)
3Impurities in styrene 60m Innowax, 2ml/min He, 1l split 80:1, 80C (9min), 5C/min to 150C
![Page 4: 1 Gas Chromatography (GC; GLC; GSC) “Basic Gas Chromatography” by McNair, Wiley, 1997 “Modern Practise in GC” by Grob, pp. 900 “Gas Chromatography” by](https://reader035.vdocuments.us/reader035/viewer/2022062407/56649da25503460f94a8f9e2/html5/thumbnails/4.jpg)
4Schematic gas chromatograph Carrier gas (high purity, unreactive, cheap): N2, He, H2
Flow control» constant, reproducible flow rate
Injection port (sample inlet, microlitre syringe) Oven — thermostatted at constant T or linear rate Column Detector Data processing
» retention time (volume)» peak area» recorder, integrator, microprocessor, computer, etc
![Page 5: 1 Gas Chromatography (GC; GLC; GSC) “Basic Gas Chromatography” by McNair, Wiley, 1997 “Modern Practise in GC” by Grob, pp. 900 “Gas Chromatography” by](https://reader035.vdocuments.us/reader035/viewer/2022062407/56649da25503460f94a8f9e2/html5/thumbnails/5.jpg)
5Powerful analytical tool — why? Very large separating power
– para (138.4C), ortho (144.4C) & meta (139.1C) xylene High speed of analysis
– no sample pre-treatment usually Quantitative analysis
– excellent High sensitivity
– 58 ppm of phenylacetylene (#11) in styrene sample Qualitative analysis the Achilles heel!
– Just because peak at 18 min is labelled -methylstyrene Simple to use and operate
– unskilled, automatic, low cost
![Page 6: 1 Gas Chromatography (GC; GLC; GSC) “Basic Gas Chromatography” by McNair, Wiley, 1997 “Modern Practise in GC” by Grob, pp. 900 “Gas Chromatography” by](https://reader035.vdocuments.us/reader035/viewer/2022062407/56649da25503460f94a8f9e2/html5/thumbnails/6.jpg)
6Qualitative analysis Identification based on
retention times (volumes)
Not conclusive even by comparing two or more different columns
If analytes known then reasonable supposition
Unambiguous?– GC + MS or– GC + IR
Mixture of unknown alcohols
knowns
n-amyl
![Page 7: 1 Gas Chromatography (GC; GLC; GSC) “Basic Gas Chromatography” by McNair, Wiley, 1997 “Modern Practise in GC” by Grob, pp. 900 “Gas Chromatography” by](https://reader035.vdocuments.us/reader035/viewer/2022062407/56649da25503460f94a8f9e2/html5/thumbnails/7.jpg)
7Quantitative analysis 5.00 ml of a soln containing an internal standard, S, of
concentration 100 g/ml were added to a soln of unknown, X. Chromatography of the mixture gave an area ratio of (AX / AS) = 0.81 ± 0.01.
Calibration of known weight ratio mixes gave:– weight ratio, W = (WX / WS) 0.20 0.40 0.80– area ratio, A = (AX / AS) 0.23 0.46 0.91
Calculate weight of X in unknown.» By least-squares: A = 1.132 W + 0.005 so if A = 0.81 then
W = 0.711 but WS = 500 g WX = 356 g
![Page 8: 1 Gas Chromatography (GC; GLC; GSC) “Basic Gas Chromatography” by McNair, Wiley, 1997 “Modern Practise in GC” by Grob, pp. 900 “Gas Chromatography” by](https://reader035.vdocuments.us/reader035/viewer/2022062407/56649da25503460f94a8f9e2/html5/thumbnails/8.jpg)
8Detectors — key components Flame ionization family
– the parent FID — workhorse, quasi-universal, reliable– flame photometric FPD — #6 sulphur/phosphorus detector– alkali flame AFID or nitrogen/phosphorus NPD or TID
Electron capture – ECD — #5 halothane in blood analysis– very high sensitivity, very selective
Thermal conductivity– TCD or HWD or katharometer– robust, universal, low sensitivity
Mass spectrometer MSD — expensive but worth it– excellent for identification
![Page 9: 1 Gas Chromatography (GC; GLC; GSC) “Basic Gas Chromatography” by McNair, Wiley, 1997 “Modern Practise in GC” by Grob, pp. 900 “Gas Chromatography” by](https://reader035.vdocuments.us/reader035/viewer/2022062407/56649da25503460f94a8f9e2/html5/thumbnails/9.jpg)
9Flame ionisation detector(s) FID (basic design)
– mix H2 and carrier, burn in clean dust-free air
– collect ions formed– current eluting cpds
AFID (N/P sensitive)– surround jet by alkali salt– surface catalysed reactions
FPD (collect photons emitted)– Sulphur mode 394 nm– Phosphorus mode 526 nm
AI R
HYDROGEN
CARRI ER
SI GNAL
COLLECT ORELECT RODE
FLAME
![Page 10: 1 Gas Chromatography (GC; GLC; GSC) “Basic Gas Chromatography” by McNair, Wiley, 1997 “Modern Practise in GC” by Grob, pp. 900 “Gas Chromatography” by](https://reader035.vdocuments.us/reader035/viewer/2022062407/56649da25503460f94a8f9e2/html5/thumbnails/10.jpg)
10Flame ionization detector MDQ — 5 picograms / second Response — quasi-universal Linearity — excellent (over 106) Stability — flow and temperature insensitive Temperature limit — 400 C Carrier gas — Nitrogen, helium or hydrogen Summary
– Rugged– non-responsive to water and air (“inorganics”)– destructive and – very widely used
![Page 11: 1 Gas Chromatography (GC; GLC; GSC) “Basic Gas Chromatography” by McNair, Wiley, 1997 “Modern Practise in GC” by Grob, pp. 900 “Gas Chromatography” by](https://reader035.vdocuments.us/reader035/viewer/2022062407/56649da25503460f94a8f9e2/html5/thumbnails/11.jpg)
11Flame photometric detector MDQ — 1 nanogram S (394 nm); 0.1 ng P (526 nm) Response — effectively only S and P compounds Linearity — moderate (104) Stability — good Temperature limit — 400 C Carrier — nitrogen Summary
– very selective– flame needs clean hydrogen/air supply– expensive but invaluable for pesticide and air pollution work
![Page 12: 1 Gas Chromatography (GC; GLC; GSC) “Basic Gas Chromatography” by McNair, Wiley, 1997 “Modern Practise in GC” by Grob, pp. 900 “Gas Chromatography” by](https://reader035.vdocuments.us/reader035/viewer/2022062407/56649da25503460f94a8f9e2/html5/thumbnails/12.jpg)
12Flame photometric detector Sulphur mode; 394 nm
– large solvent peak– small hydrocarbon peak
(pentadecane) for 4,000 ng– dodecanethiol (IS) 20 ng– methyl parathion 20 ng
Phosphorus mode; 526 nm– tiny solvent peak– tributyl phosphate (IS) 20 ng– methyl parathion 20 ng
Same sample in both cases
![Page 13: 1 Gas Chromatography (GC; GLC; GSC) “Basic Gas Chromatography” by McNair, Wiley, 1997 “Modern Practise in GC” by Grob, pp. 900 “Gas Chromatography” by](https://reader035.vdocuments.us/reader035/viewer/2022062407/56649da25503460f94a8f9e2/html5/thumbnails/13.jpg)
13Hot Wire Detector (TCD)
Tungsten-rhenium filaments– Current of 0.3 A at 16 V
Temperature of filament?350 C but depends on
thermal conductivity of gas flowing over hot wire
Resistance of wire changes as T changes– Pre & post column detection
CURRENTCARRI ERGAS FLOW
COLUMNGAS FLOW
SI GNAL
![Page 14: 1 Gas Chromatography (GC; GLC; GSC) “Basic Gas Chromatography” by McNair, Wiley, 1997 “Modern Practise in GC” by Grob, pp. 900 “Gas Chromatography” by](https://reader035.vdocuments.us/reader035/viewer/2022062407/56649da25503460f94a8f9e2/html5/thumbnails/14.jpg)
14Thermal conductivity detector
MDQ — 10 nanograms (about 50 ppm) Response — universal (all except the carrier) Linearity — moderate (104) Stability — flow and temperature sensitive Carrier — hydrogen or helium Temperature limit — 400 C Summary
– non-destructive and simple to operate (portable)– moderate stability and sensitivy– used for fixed gas analysis, eg, H2, N2, O2, CO2, Ar, etc
![Page 15: 1 Gas Chromatography (GC; GLC; GSC) “Basic Gas Chromatography” by McNair, Wiley, 1997 “Modern Practise in GC” by Grob, pp. 900 “Gas Chromatography” by](https://reader035.vdocuments.us/reader035/viewer/2022062407/56649da25503460f94a8f9e2/html5/thumbnails/15.jpg)
15Electron capture detector Radioactive source emits
-particles (fast electrons) which are converted into slow electrons by collision with N2 carrier gas
These are captured by molecules to form a slower moving anions
Reduction in current as compound flows through detector
amplifi er signal
63Ni or 3H
+
carr ier gas
![Page 16: 1 Gas Chromatography (GC; GLC; GSC) “Basic Gas Chromatography” by McNair, Wiley, 1997 “Modern Practise in GC” by Grob, pp. 900 “Gas Chromatography” by](https://reader035.vdocuments.us/reader035/viewer/2022062407/56649da25503460f94a8f9e2/html5/thumbnails/16.jpg)
16ECD: organohalogen pesticides
Column DB-210+ 15 m x 0.53 mm id; film 1.0 m He carrier; 100-220C at 3C/min. 600pg each
– 2-lindane; 4-aldrin; 9-dieldrin; 13-DDT
![Page 17: 1 Gas Chromatography (GC; GLC; GSC) “Basic Gas Chromatography” by McNair, Wiley, 1997 “Modern Practise in GC” by Grob, pp. 900 “Gas Chromatography” by](https://reader035.vdocuments.us/reader035/viewer/2022062407/56649da25503460f94a8f9e2/html5/thumbnails/17.jpg)
17Electron capture detector MDQ — very high sensitivity (picogram range) Response — very selective (halogenated compounds only)
Linearity — Poor ( 500 to 104) Stability — fair Temperature limit — 220 C (3H) or 350 C (Ni) Carrier — nitrogen or argon + 10% methane Summary
– easily contaminated, carrier must be dry– non-destructive– requires license for radioactive source
![Page 18: 1 Gas Chromatography (GC; GLC; GSC) “Basic Gas Chromatography” by McNair, Wiley, 1997 “Modern Practise in GC” by Grob, pp. 900 “Gas Chromatography” by](https://reader035.vdocuments.us/reader035/viewer/2022062407/56649da25503460f94a8f9e2/html5/thumbnails/18.jpg)
18ECD; biphenyls at 30 ppb eachMDQ: 10 fg lindane in 2l injection
![Page 19: 1 Gas Chromatography (GC; GLC; GSC) “Basic Gas Chromatography” by McNair, Wiley, 1997 “Modern Practise in GC” by Grob, pp. 900 “Gas Chromatography” by](https://reader035.vdocuments.us/reader035/viewer/2022062407/56649da25503460f94a8f9e2/html5/thumbnails/19.jpg)
19The column Two kinds
– capillary (WCOT: 0.2 to 5 m film thickness, PLOT) » 0.3mm id 50m 300,000 plates 0.01ml 2 ml/min
– packed » 3mm id 2m 3,000 plates 10ml 40 ml/min
Liquid phase– low vapour pressure over operating range & thermally stable – chemically inert to solutes– good solvent for solutes used and low viscosity
Temperature– isothermal– programmed (linear, reproducible)
![Page 20: 1 Gas Chromatography (GC; GLC; GSC) “Basic Gas Chromatography” by McNair, Wiley, 1997 “Modern Practise in GC” by Grob, pp. 900 “Gas Chromatography” by](https://reader035.vdocuments.us/reader035/viewer/2022062407/56649da25503460f94a8f9e2/html5/thumbnails/20.jpg)
20Packed columns (SS, glass)
¼ or ½“od; coiled, U-shaped Solid support
– uniform pore diameter (10m or less)– large inert surface area (AW, treated with DMCS)– regularly shaped, uniformly sized (mesh nos.)– eg Chromosorb W/AW/DMCS 100-120 mesh
Preparation (5% X on Y):– slurry 5g liquid phase X with 100g solid support Y in
small quantity of suitable solvent– Rotovap off solvent, pack column– Leave overnight at highest safe temperature in oven
with flow of carrier
![Page 21: 1 Gas Chromatography (GC; GLC; GSC) “Basic Gas Chromatography” by McNair, Wiley, 1997 “Modern Practise in GC” by Grob, pp. 900 “Gas Chromatography” by](https://reader035.vdocuments.us/reader035/viewer/2022062407/56649da25503460f94a8f9e2/html5/thumbnails/21.jpg)
21Effect of column temperature Increasing the column temperature reduces retention times– biggest effect on longest
times Conflict: analysis time
versus resolution Temperature programming
sidesteps problem– initial, final, rate of climb
and timings
![Page 22: 1 Gas Chromatography (GC; GLC; GSC) “Basic Gas Chromatography” by McNair, Wiley, 1997 “Modern Practise in GC” by Grob, pp. 900 “Gas Chromatography” by](https://reader035.vdocuments.us/reader035/viewer/2022062407/56649da25503460f94a8f9e2/html5/thumbnails/22.jpg)
22Solute classes
Based on H-bonding capability
– Weak bond I Polyalcohols, amino alcohols, etc II AlcoholsIII Ethers, ketonesIV Aromatics, olefins, halocarbons V Saturated hydrocarbons
![Page 23: 1 Gas Chromatography (GC; GLC; GSC) “Basic Gas Chromatography” by McNair, Wiley, 1997 “Modern Practise in GC” by Grob, pp. 900 “Gas Chromatography” by](https://reader035.vdocuments.us/reader035/viewer/2022062407/56649da25503460f94a8f9e2/html5/thumbnails/23.jpg)
23“Liquid” phase — the heart of the GC
‘Polarity’
Squalane — the standard phase with zero polarity
Silicone gum SE30/OV-1 100-300C 220 Dexsil 300 50-400C 470 Di-nonylphthalate 0-150C 790 OV-210 silicone 20-275C 1500 Polyethylene glycol (CarboWax) 60-225C 2300 OV-275 silicone 100-275C 4200
![Page 24: 1 Gas Chromatography (GC; GLC; GSC) “Basic Gas Chromatography” by McNair, Wiley, 1997 “Modern Practise in GC” by Grob, pp. 900 “Gas Chromatography” by](https://reader035.vdocuments.us/reader035/viewer/2022062407/56649da25503460f94a8f9e2/html5/thumbnails/24.jpg)
24RTX-200 (trifluoropropylmethyl polysiloxane)
![Page 25: 1 Gas Chromatography (GC; GLC; GSC) “Basic Gas Chromatography” by McNair, Wiley, 1997 “Modern Practise in GC” by Grob, pp. 900 “Gas Chromatography” by](https://reader035.vdocuments.us/reader035/viewer/2022062407/56649da25503460f94a8f9e2/html5/thumbnails/25.jpg)
25
Stabilwax (Carbowax PEG 20M)
![Page 26: 1 Gas Chromatography (GC; GLC; GSC) “Basic Gas Chromatography” by McNair, Wiley, 1997 “Modern Practise in GC” by Grob, pp. 900 “Gas Chromatography” by](https://reader035.vdocuments.us/reader035/viewer/2022062407/56649da25503460f94a8f9e2/html5/thumbnails/26.jpg)
26Specialised applications Pyrolysis
– brake lining dust Headspace analysis
– black peppercorns or cola can Multicolumn techniques
– dual– back-flushing– heart-cutting
Hyphenated– GC + MS– GC/FTIR
Preparative GC
![Page 27: 1 Gas Chromatography (GC; GLC; GSC) “Basic Gas Chromatography” by McNair, Wiley, 1997 “Modern Practise in GC” by Grob, pp. 900 “Gas Chromatography” by](https://reader035.vdocuments.us/reader035/viewer/2022062407/56649da25503460f94a8f9e2/html5/thumbnails/27.jpg)
Pyrogram
![Page 28: 1 Gas Chromatography (GC; GLC; GSC) “Basic Gas Chromatography” by McNair, Wiley, 1997 “Modern Practise in GC” by Grob, pp. 900 “Gas Chromatography” by](https://reader035.vdocuments.us/reader035/viewer/2022062407/56649da25503460f94a8f9e2/html5/thumbnails/28.jpg)
27Headspace analysis of 0.1% cpd in water
![Page 29: 1 Gas Chromatography (GC; GLC; GSC) “Basic Gas Chromatography” by McNair, Wiley, 1997 “Modern Practise in GC” by Grob, pp. 900 “Gas Chromatography” by](https://reader035.vdocuments.us/reader035/viewer/2022062407/56649da25503460f94a8f9e2/html5/thumbnails/29.jpg)
28Multi-column techniques
Backflushing to vent» speeding up analysis of A, B by not bothering with C, D
Heart-cutting» analyse for B in the presence of large amounts of interfering A
Dual column for difficult separations» 1st column can separate A & B but not C & D; 2nd col vice-versa
A B C D SV D C B A * DD C B
A B C D SV B A DD C
A B C D SV
D C
DD + C B A
V e n t m o s t o f A
V e n t D + C