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