This preview shows page 1. Sign up to view the full content.
Unformatted text preview: to
low-polarity bonded phase and more polar
mobile phase. 1/11/2012 CHEM2202 WTCHAN 22 Normal phase – polar stationary phase
Reverse phase – non-polar stationary phase 1/11/2012 CHEM2202 WTCHAN 23 In reverse phase chromatography, the more
polar solutes in a sample have less affinity for
the nonpolar stationary phase
Polar components spend less time in the stationary phase
and more time in the more polar mobile phase
Polar components will elute first
Compounds will come off the column in order of
decreasing polarity 1/11/2012 CHEM2202 WTCHAN 24 The general elution problem of liquid
chromatography: analytes in a sample have a
wide range of k’ values for any combination of
stationary and mobile phases
The solution to the general elution problem is to decrease the
values of k’ for the analytes while the elution is occurring.
In reverse phase chromatography, the affinity of the
mobile phase is increased by making the mobile phase less
polar. Thus, as the elution continues, an increasing amount
of a less polar solvent is mixed into the mobile phase.
This is called gradient elution.
gradient 1/11/2012 CHEM2202 WTCHAN 26 Common solvents for LC are water, acetonitrile,
methanol, and tetrahydrofuran 1/11/2012 CHEM2202 WTCHAN 27 According to European Directive 67/548/EEC as amended.
Highly flammable. Harmful by inhalation, in contact with skin and if swallowed. Irritating to eyes. 1/11/2012 CHEM2202 WTCHAN 28 Common characteristics of the solvents for LC
include: low viscosity, available in high purity,
UV-transparent, and miscible in each other 1/11/2012 CHEM2202 WTCHAN 29 In gradient elution, the polarity of the mobile phase
is varied continuously during the elution process by
combining two or more solvents in different
proportion in a pre-defined program 1/11/2012 CHEM2202 WTCHAN 30 1/11/2012 CHEM2202 WTCHAN 31 Melamine 三聚氰胺
1/11/2012 CHEM2202 WTCHAN 32 Determination of Melamine Residues in
Catfish Tissue by Triple Quadrupole LC-MSMS with HILIC Chromatography – US FDA
View Full Document