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Food Analysis Lecture 24 (4/22/2005)

Food Analysis Lecture 24 (4/22/2005). Gas Chromatography. Qingrong Huang Department of Food Science Read Material: Chapter 29, page 479 Final Exam: April 29. Gas Chromatography (1). First introduced in 1952, first commercial instrument: 1956;

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Food Analysis Lecture 24 (4/22/2005)

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  1. Food Analysis Lecture 24 (4/22/2005) Gas Chromatography Qingrong Huang Department of Food Science Read Material: Chapter 29, page 479 Final Exam: April 29

  2. Gas Chromatography (1) • First introduced in 1952, first commercial instrument: 1956; • good for thermally stable volatile compounds; • Sample preparation: • (1) Headspace methods: one of the simplest methods, only good for • volatiles in headspace at C>10-7 g/L; • - Direct headspace sampling; • - Headspace concentration techniques or purge and trap methods: • (2) Distillation methods: • (3) Solvent extraction: preferred for the recovery of volatiles from • food; use of two immiscible phases (water and an organic solvent) • (4) Solid-phase microextraction (SPME): new and rapidly growing

  3. SPME • Microextraction technique which employs a thin film of sorptive polymer on a glass fiber • Fiber • Having varying film thickness of polymer • Coatings are based on both absoption and adsorption mechanisms • Convenient, solventless extraction technique • Used to extract analytes from both liquid and solid matrices

  4. SPME Advantages • less solvent required • speed • less glassware is needed • better precision and accuracy • minimal solvent evaporation • readily automated

  5. SPME Device

  6. SPME Procedure Extraction Desorption

  7. Sample Injection • Direct Injection • Sample Derivatization

  8. Components of GC • Gas supply and regulators; • Injection port; • Oven; • Column; • Detector; • Electronic; • Recorder/data handling system.

  9. Diagram of GC System

  10. Gas Supply System • Carrier gas and gas for the detector • For detector: air and hydrogen • High purity gas • Gas lines, regulators, and fittings are good quality

  11. Injection Port • Providing a place for sample introduction, vaporization; • 20 °C above the maximum column oven temperature.

  12. OVEN • Control the temperature of column • Determined by the interaction of the analyte with the stationary • phase and the boiling point for separation of compounds • For temperature-programmed runs, 2-10 °C/min

  13. Column • Either packed or capillary column • Packaging Materials: • - Packed column: silane-treated diatomaceous earth • - Capillary column: hollow fused silica glass • Stationary phase: - polysiloxane-based (-Si-O-Si-) • -General rules: choose polar phase to separate polar compounds • and phenyl-based column to separate aromatic compounds.

  14. Detector • Thermal Conductivity Detector (TCD) • Flame Ionization Detector (FID) • Electron Capture (ECD) • Flame Photometric Detector (FPD) • Photoionization Detector (PID)

  15. Carrier Gas • In capillary chromatography, A term is small; • N2 is the most efficient carrier gas, but its minimum occur in low u; • Hydrogen is a better choice than He and N2

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