intensive general chemistry chemical separations ii isabelle vu trieu [email protected]
TRANSCRIPT
Intensive General Chemistry
Chemical separations II
Isabelle Vu Trieu [email protected]://ull.chemistry.uakron.edu
Gas versus Liquid chromatography
Phase 1
Phase 2
A A A
A
A
A
A
AAA
A
Partition constant: K = aA(stationary)/ aA(mobile)
Mobilephase
Stationaryphase
Gas or Liquid
Chromatography - Principles
Retention time (tr) : time required for a given component to emerge from the column
Retention volume (Vr) : volume of mobile phase required for a given component to emerge from the column
Vr = tr x F
Flow rate
A typical chromatogram
Retention time
Hold-up timeAdjusted retention time
Qualitative / quantitative analysis
Qualitative– “Blind” method
– Indicate the presence /absence of a substance (not what it is)
– Only one piece of information (Tr)
Quantitative– Analysis based on:
• Peak height
• Peak area
– Calibration & standards• External standard
• Internal standard
GC instrumentation
Carrier gas
Injection port
Columns
wide bore
Higher capacity Better resolution
capillaryOpen (coated)
Detectors
Thermal conductivity– General purpose
– Non destructive
– Detect the change in resistance of a wire based on variations of the thermoconductivity of the gas evolving from the column
Flame ionization– Specific (combustible
sample only)
– Destructive
– Measure the current due to the production of ions when burning the sample in a flame
HPLC equipment
Sample injector
Sampling Loop system:
Columns:
Normal phase– Stationary phase is
polar• Ex: silica, alumina
– Mobile phase is non-polar
• Ex: hexane
Reverse-phase– Stationary phase is
non-polar• Ex: carbon chain
bonded to silica
– Mobile phase is polar• Ex: water, methanol
Columns are packed, typically 10-20 cm long, 5mm id
Detector: