《仪器分析 Instrumental Analysis》课程教学资源（教材讲义）15_Gas Chromatography

Gas Chromatography (Chapter 27) Two major types Gas-solid chromatography (stationary phase:solid) Gas-liquid chromatography (stationary phase:immobilized liquid) Retention Volume: VR=tR·F VM=tM.F retained non-retained average volumetric flow rate (mL/min) F can be estimated by measuring flow rate exiting the column using soap bubble meter (some gases dissolving in soap solution) but measured VR and VM depend on pressure inside column temperature of column CEM 333 page 15.1

Gas Chromatography (Chapter 27) Two major types • Gas-solid chromatography (stationary phase: solid) • Gas-liquid chromatography (stationary phase: immobilized liquid) Retention Volume: VR = tR ×F retained 1 4 2 4 3 VM = tM ×F non-retained 1 4 2 4 3 average volumetric flow rate (mL/min) F can be estimated by measuring flow rate exiting the column using soap bubble meter (some gases dissolving in soap solution) but measured VR and VM depend on • pressure inside column • temperature of column CEM 333 page 15.1

VR and VM depend on average pressure inside column Column has resistance to flow At inlet,P=high,F=low P.F=constant At outlet.P=low.F=high/ Pressure drop factor j used to calculate average pressure from inlet pressure Pinlet and outlet pressure Poutlet 3(Pinlet /Poutlet)-1 j= 2(Pinlet /Poutlet)-1 Corrected Retention Volume: VR=j.tR-F VM =j.tM.F Specific Retention Volume: Vg=,8x 273 M. column correction for temperature mass of stationary phase partition ratio cs/cm K 273 一× Tcolumn density of stationary phase Vg -semi-useful parameter for identifying species eluting often scales with vapor pressure (constant polarity analytes) CEM 333 page 15.2

VR and VM depend on average pressure inside column Column has resistance to flow At inlet , P = high, F = low At outlet, P = low, F = high ö ø ÷ P×F = constant Pressure drop factor j used to calculate average pressure from inlet pressure Pinlet and outlet pressure Poutlet j = 3 Pinlet / Poutlet ( ) 2 -1 [ ] 2 Pinlet ( / Poutlet) 3 -1 [ ] Corrected Retention Volume: VR 0 = j×tR ×F VM 0 = j×tM ×F Specific Retention Volume: Vg = VR 0 - VM 0 Ms ´ 273 Tcolumn correction for temperature 1 4 2 4 3 mass of stationary phase partition ratio cs/cm Vg = K rstationary ´ 273 Tcolumn density of stationary phase Vg - semi-useful parameter for identifying species eluting - often scales with vapor pressure (constant polarity analytes) CEM 333 page 15.2

GC Instrumentation (Fig 27-1): Soap-bubble meter Recorder Syringe Detecto Two-stage Injector troller 00 Carrier Column Column oven Carrier gas:He(common).N2.H2 Pinlet 10-50 psig F=25-150 mL/min packed column F=1-25 mL/min open tubular column Column: 2-50 m coiled stainless steel/glass/Teflon Oven: 0-400 C average boiling point of sample accurate to <1 C Detectors: FID,TCD,ECD,(MS) CEM 333 page 15.3

GC Instrumentation (Fig 27-1): Carrier gas: He (common), N2, H2 Pinlet 10-50 psig F=25-150 mL/min packed column F=1-25 mL/min open tubular column Column: 2-50 m coiled stainless steel/glass/Teflon Oven: 0-400 °C ~ average boiling point of sample accurate to <1 °C Detectors: FID, TCD, ECD, (MS) CEM 333 page 15.3

Sample injection: direct injection into heated port (>Toven)using microsyringe (i)1-20 uL packed column (ii)10-3 uL capillary column Syringe Septum P=0.25 psi mL- connector Column Fig 27-3 rotary sample valve with sample loop Eluent Eluent to column column (b) Fig27-4 CEM 333 page 15.4

Sample injection: - direct injection into heated port (>Toven) using microsyringe (i) 1-20 mL packed column (ii) 10-3 mL capillary column Fig 27-3 - rotary sample valve with sample loop Fig 27-4 CEM 333 page 15.4

Split injection: routine method 0.1-1%sample to column remainder to waste Splitless injection: all sample to column best for quantitative analysis only for trace analysis,low [sample] On-column injection: for samples that decompose above boiling point no heated injection port column at low temperature to condense sample in narrow band heating of column starts chromatography CEM 333 page 15.5

Split injection: routine method 0.1-1 % sample to column remainder to waste Splitless injection: all sample to column best for quantitative analysis only for trace analysis, low [sample] On-column injection: for samples that decompose above boiling point - no heated injection port column at low temperature to condense sample in narrow band heating of column starts chromatography CEM 333 page 15.5

GC Detectors: Need Sensitive (10-8-10-15 g solute/s) Operate at high T(0-400 C) Stable and reproducible ·Linear response Desire ·Wide dynamic range ·Fast response ·Simple(reliable) ·Nondestructive Uniform response to all analytes CEM333 page 15.6

GC Detectors: Need • Sensitive (10-8-10-15 g solute/s) • Operate at high T (0-400 °C) • Stable and reproducible • Linear response Desire • Wide dynamic range • Fast response • Simple (reliable) • Nondestructive • Uniform response to all analytes CEM 333 page 15.6

Flame Ionization Detector (FID) detector -Collector holder Insulator nu Ha-air flame Inside oven wall of en Fig 27-6 ·Rugged Sensitive (10-13 g/s) Wide dynamic range (107) Signal depends on C atoms in organic analyte-mass sensitive not concentration sensitive Weakly sensitive to carbonyl,amine,alcohol,amine groups Not sensitive to non-combustibles-H2O,CO2,SO2,NOx ·Destructive CEM 333 page 15.7

Flame Ionization Detector (FID): Fig 27-6 • Rugged • Sensitive (10-13 g/s) • Wide dynamic range (107) • Signal depends on # C atoms in organic analyte - mass sensitive not concentration sensitive • Weakly sensitive to carbonyl, amine, alcohol, amine groups • Not sensitive to non-combustibles - H2O, CO2, SO2, NOx • Destructive CEM 333 page 15.7

Thermal Conductivity Detector(TCD) Flow out Flow in (a) Fig 27-7 Thermal conductivity of He,H2 much larger than organics Organics cause T rise in filament ·Rugged Wide dynamic range(105) ·Nondestructive Insensitive (10-8 g/s)-non-uniform CEM333 page 15.8

Thermal Conductivity Detector (TCD) Fig 27-7 Thermal conductivity of He, H2 much larger than organics Organics cause T rise in filament • Rugged • Wide dynamic range (105) • Nondestructive • Insensitive (10-8 g/s) - non-uniform CEM 333 page 15.8

Electron Capture Detector (ECD): Insulato Electrode Electrode Fig 27-8 Electrons from B-source ionize carrier gas Organic molecules capture electrons and decrease current ·Simple and reliable Sensitive (10-15 g/s)to electronegative groups (halogens, peroxides) Largely non-destructive Insensitive to amines,alcohols and hydrocarbons Limited dynamic range(102) Important Other Detectors: AES,AAS,chemiluminescent reaction(S),mass spectrometer, FTIR CEM 333 page 15.9

Electron Capture Detector (ECD): Fig 27-8 Electrons from b-source ionize carrier gas Organic molecules capture electrons and decrease current • Simple and reliable • Sensitive (10-15 g/s) to electronegative groups (halogens, peroxides) • Largely non-destructive • Insensitive to amines, alcohols and hydrocarbons • Limited dynamic range (102) Important Other Detectors: • AES, AAS, chemiluminescent reaction (S), mass spectrometer, FTIR CEM 333 page 15.9

Column Stationary Phases: Packed liquid coated silica particles (<100-300 um diameter)in glass tube best for large scale but slow and inefficient Capillary/Open Tubular wall-coated (WCOT)<1 um thick liquid coating on inside of silica tube support-coated(SCOT)30 um thick coating of liquid- coated support on inside of silica tube best for speed and efficiency but only small samples diameter 150-400μm WCOT SCOT support particles immobilized liquid 1 um (diatomaceous earth)30μm CEM 333 page 15.10

Column Stationary Phases: Packed • liquid coated silica particles (<100-300 mm diameter) in glass tube • best for large scale but slow and inefficient Capillary/Open Tubular • wall-coated (WCOT) <1 mm thick liquid coating on inside of silica tube • support-coated (SCOT) 30 mm thick coating of liquid￾coated support on inside of silica tube • best for speed and efficiency but only small samples WCOT SCOT diameter 150-400 mm immobilized liquid 1 mm support particles (diatomaceous earth) 30 mm CEM 333 page 15.10