10/27/11 1 Lecture 22– Oct 28 Chem 4101 – Fall 2011 Gas Chromatography 1- Principles 2- Instrumentation 3- Applications Sections 27A, B, C, D, F Suggested exercises: 27-4, 27-14, 27-15, 27-16, 27-23, 27-24, 27-5, 27-8, 27-9, 27-19, 27-25 Lecture 22– Oct 28 Chem 4101 – Fall 2011 Instrumentation Figure 27-1, Sections 27B Lecture 22– Oct 28 Chem 4101 – Fall 2011 Figures 27-6, 27-21; Sections 27C 27F Open column with solid porous support GC chromatogram10/27/11 2 Lecture 22– Oct 28 Chem 4101 – Fall 2011 Mobile and stationary phases Thin film (1 µm) (Fused-silica, wall-coated open tubular column) Polydimethyl siloxane [R=CH3] or other polymers such as 5% Phenyl-polydimethylsiloxane [95%, R=CH3; 5%, R = Phenyl] Thermal stability up to 350 °C Mobile phase (Carrier gas) He (Ar, N2, H2) 1-25 mL/min Section 27C-4 Stationary Phase Lecture 22– Oct 28 Chem 4101 – Fall 2011 Equations and terminology Parameters Retention volumes Retained and non-retained Volumetric flow rate Measured flow rate (Eq. 27-3) Corrected retention volumes Pressure differential (F, j) Temperature differential (F) Retention and dead volumes, Equations 27-1, 27-2, 27-4 € tR=VRF € tM=VMF € VR=VR0j € VM=VM0j € j =3 ×PiP 2−1 2 ×PiP 3−1 Compressibility factor, Equation 27-5 Lecture 22– Oct 28 Chem 4101 – Fall 2011 van Deemter Plot-GC Figure 26-8, Sections 26C-3 € H = A +Bu+ CSu + CMu10/27/11 3 Lecture 22– Oct 28 Chem 4101 – Fall 2011 Figures 27-3 and -4, Sections 27B Sample Introduction Direct injection – -0.1 to 20µL. Injected volume: 1/100 or less of column. Temperature: At least 50 °C above the boiling point of the least volatile component Lecture 22– Oct 28 Chem 4101 – Fall 2011 Figure 27-5, Sections 27B Rotary Sample Valve Sampling! Delivery to the column!Reproducibility better than 0.5% Lecture 22– Oct 28 Chem 4101 – Fall 2011 GC Columns Section 27C FSWC = Fused silica, wall coated, open tubular column WCOT = Wall coated, open tubular column (metal, glass, plastic) SCOT = support-coated, open tubular column PLOT = porous-layer, open tubular column (= SCOT) Ideal requirements: (i) Boiling at > 100 °C above the maximum oven temperature (ii) Thermal stability (iii) Chemical inertness, (iv) Mobile phase that provides good capacity factor (k) and selectivity10/27/11 4 Lecture 22– Oct 28 Chem 4101 – Fall 2011 Stationary phases Section 27C-4 Poly-Siloxanes Poly-Ethylene glycols HO - CH2 - CH2 -(O - CH2 - CH2)n - OH Liquid, 0.30 µm thick film Blocking silanol groups prevents adsorption – (tailing) Silanization (page 802). Lecture 22– Oct 28 Chem 4101 – Fall 2011 Section 27C GLC Columns Stationary Phase Analytes Polar: -CN, -CO, -OH Alcohols, amines, carboxilic acids Medium: blends Ethers, ketones, aldehydes Non polar: hydrocarbon or dialkylsiloxane hydrocarbons Lecture 22– Oct 28 Chem 4101 – Fall 2011 Section 27C GLC Columns McReynolds Constants – See Analytical Chemistry Handbook (J.A. Dean)10/27/11 5 Lecture 22– Oct 28 Chem 4101 – Fall 2011 Analytes and stationary phases Section 27A, Figure 27-17 OV-1 OV-3 OV-17 Carbowax 20M OV-210 OV-275 Lecture 22– Oct 28 Chem 4101 – Fall 2011 Section 27B GC Detectors Ideal characteristics: 1. Adequate sensitivity and detection limit 2. Good stability and reproducibility 3. Linear response over several orders of magnitude 4. Adequate temperature range (e.g. up to 400 °C) 5. Short response time and independent of flow rate 6. High reliability and ease of use 7. Similar response toward all analytes 8. Non destructive Lecture 22– Oct 28 Chem 4101 – Fall 2011 Flame ionization detector (FID) Figure 27-8, Section 27B Amount of ions are proportional to the number of reduced C atoms. Limit of detection (10-13 g/s), Linear dynamic range 107 Destructive MASS SENSITIVE DETECTOR – (Not affected by dilution) Insensitive toward H20, CO2, SO2, CO, noble gases, and NOx10/27/11 6 Lecture 22– Oct 28 Chem 4101 – Fall 2011 Figure 27-47, Section 27C GC-MS Capillary column Ionization: Electron impact or Chemical Analyzer: Quadrupoles and ion traps (MS or MS/MS) Duty cycle: one scan per second. Total ion chromatogram or extracted ion current Lecture 22– Oct 28 Chem 4101 – Fall 2011 Applications Retention volumes and times – qualitative identification Purity Monitor purification procedures Determination of retention indexes (Kovats’ index) Peak heights or areas – quantitative information Response factors Standards for calibration curve Internal standards to improve reproducibility Isothermal and thermal gradients (Figure 27-19) Volatile, thermally stable species Derivatization may be
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