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Effect of Packing Particle Size on Plate Height

Effect of Packing Particle Size on Plate Height. Resolution between 2 adjacent peaks. The General Elution Problem. Small k′. Large k′. The General Elution Problem. 1. Poor separation of compounds with small capacity factors. 2. Excessive separation time and poor

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Effect of Packing Particle Size on Plate Height

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  1. Effect of Packing Particle Size on Plate Height

  2. Resolution between 2 adjacent peaks

  3. The General Elution Problem Small k′ Large k′

  4. The General Elution Problem 1. Poor separation of compounds with small capacity factors. 2. Excessive separation time and poor detectability of compounds with large capacity factors.

  5. Solutions to The General Elution Problem Alter k′ values during the separation: 1. Temperature Program (GC) 2. Gradient Elution (LC) 3. Coupled Columns (change the stationary phase) Temperature programming and gradient elution require “re-equilibration time” after the analysis of each sample.

  6. Temperature Programming: Separation of Normal Alkanes (C6 – C12) Ti = 100oC Tf = 200oC Tc = 130oC 25 12 0 0

  7. Gradient Elution: Substituted Benzenes Organic Water

  8. GAS CHROMATOGRAPHY

  9. GAS CHROMATOGRAPHY INSTRUMENTATION 1. Mobile Phase 2. Sample Injector 3. Column (Stationary Phase) 4. Detector

  10. GC MOBILE PHASES 1. He 2. H2 3. N2 4. CO2

  11. GC On-Column Injector

  12. GC Glass-lined Injector for a Packed Column

  13. GC Injector for a Capillary Column

  14. GC “Split” Injector for a Capillary Column

  15. GC “Split-less” Injector for a Capillary Column

  16. GC Stationary Phases PDMS: PolyDiMethylSiloxane Organic stationary phases must have sufficient molecular weight to achieve low volatility

  17. GC Stationary Phases Increase Polarity by adding phenyl rings or CN groups…

  18. GC Stationary Phases Or by de-shielding the oxygen and forming a wax. (Carbowax)

  19. GC Stationary Phases Decrease Polarity by replacing methyl groups with longer chain alkanes.

  20. GC Stationary Phases Types Non-Bonded: Liquid phase is used to coat the inside walls of the column to a thickness of about 0.1 – 1.0 μm Bonded: Silanol groups on the column wall form a chemical bond with the stationary phase

  21. GC Stationary Phases Types Preparation of Bonded Phases:

  22. GC Stationary Phases Types Advantage of Bonded Phases: 1. High Reproducibility 2. Low Bleed 3. Fast Equilibration 4. Temperature Stability 5. Easy to Back Flush 6. Long Life

  23. GC Stationary Phases Types What about Packed GC Columns?? Open Tubular Column Packed Column

  24. GC Stationary Phases Types FSOT: Fused Silica Open Tubular WCOT: Wall Coated Open Tubular SCOT: Support Coated Open Tubular WCOT and SCOT are less flexible and more fragile (made of glass) FSOT with bonded phase is most common N ≈ 400,000 H ≈ 0.1 mm L ≈ 50 m

  25. GC Stationary Phases Types Packed Column: H = A + B/u + Cu C dp2 (particle diameter)2 Open Tubular: H = B/u + Cu C  dc2 (column internal diameter)2

  26. Open Tubular Packed

  27. Packed GC Columns

  28. Open Tubular Columns tr dc [η/(Po Dm)]1/2 where: η mobile phase viscosity Po column outlet pressure Dm Diffusion coefficient of analyte in gas dc Internal column diameter Dm  MW-1/2

  29. Open Tubular Columns So: tr [η MW1/2]1/2 Gas η MW1/2 Ar 1138 CO2 995 N2 741 He 440 H2 90

  30. Open Tubular Columns with Different Gases

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