Intensive General Chemistry Chemical separations II Isabelle Vu Trieu

Gas versus Liquid chromatography Phase 1 Phase 2 A A A A A A A A A A A Partition constant: K = a A(stationary) / a A(mobile) Mobile phase Stationary phase Gas or Liquid

Chromatography - Principles 4 Retention time (t r ) : time required for a given component to emerge from the column 4 Retention volume (V r ) : volume of mobile phase required for a given component to emerge from the column V r = t r x F Flow rate

A typical chromatogram Retention time Hold-up time Adjusted retention time

Qualitative / quantitative analysis 4 Qualitative –“Blind” method –Indicate the presence /absence of a substance (not what it is) –Only one piece of information (Tr) 4 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 capillary Open (coated)

Detectors 4 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 4 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: 4 Normal phase –Stationary phase is polar Ex: silica, alumina –Mobile phase is non- polar Ex: hexane 4 Reverse-phase –Stationary phase is non-polar Ex: carbon chain bonded to silica –Mobile phase is polar Ex: water, methanol Columns are packed, typically cm long, 5mm id

Detector: