gas chromatography. chromatography – tlc (analytical) – gc (analytical) – column (preparative)...
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Gas Chromatography
Chromatography
• Chromatography– 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 – For nonpolar
material– vDW– Follows bp
• Polar– 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
OH+
Cl+
acid
base
Practical Aspectsthermometer
heat with stirring!
icebath!
thermometer
icebath!
heat with stirring!
REFLUX FIRST
DISTILL SECOND
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