Gas Chromatography
Chromatography Chromatography Strengths of TLC Weaknesses of TLC TLC (analytical) GC (analytical) Column (preparative) Strengths of TLC Weaknesses of TLC
GC Basics
Gas-Phase Separation Partitioning between mobile gas and stationary column Highly effective separations
GC Injection Column Detector Chromatogram
GC Injection
GC Column
Column Material Nonpolar Polar For nonpolar material vDW Follows bp For polar material Follows polarity
GC Detector FID TCD
GC Chromatogram Retention time Area under peak
GC Parameters and Retention Time Length of column Type of column Temperature profile Gas flow rate
Important GC Questions What is each peak? (identity) Characterization Determination of Unknown How much of each compound? (Quantity) Absolute quantity Relative quantity (product distribution)
Identity Retention time corresponds to Rf Spike with authentic sample
Gas Chromatography/Mass Spec Identifying components in mixtures Separation then identification GC-MS
Quantitation Area under peak corresponds to amount of compound causing signal Use standard plot to determine absolute concentration Use percent of total area to determine product distribution Assumes same response factor
Our Experiment How does the mechanism affect the product distribution of an elimination reaction? Conduct two elimination reactions Collect the MIXTURE of products by distillation Analyze product distribution by GC
Practical Aspects