chapter 25 lc harris
TRANSCRIPT
LC
Liquid Chromatography• Mobile phase: liquid• Stationary phase: liquid or solid• Solute: liquid• Mechanism: stronger ads. longer tr
1. Classical Liquid Chromatography2. High Performance Liquid Chromatography
http://www.youtube.com/watch?v=kz_egMtdnL4
High Performance Liquid chromatography
Normal Phase LCpolar spless polar mp
Reverse Phase LCnonpolar spmore polar mp
Classification
A. Classical Liquid Chromatography
Column: glass tube (1-5 cm dia, 50-100 cm length)sp: solid particles (150-200 m dia)mp: liquid, gravity fed
Limitations:Slow flow ratesLong separation timesResolution not great
Use: preparative chemistry/biochemistry
Smaller particle size narrower peaks
Smaller particle size small H
High Performance Liquid Chromatography
Instrument
1. Solvent delivery system
2. Pump
3. precolumn4. Injection valve
5. Column6. Detector
High Performance Liquid Chromatography
1. Solvent ReservoirsIsocratic: single solventGradient elution: vary ratio of solvents
2. PumpSteady, reproducible, constant
3. Precolumn (Guard Column)Protect more expensive analytical columnIdentical to analytical columnHelps avoid stripping stationary phase from
analytical column
4. InjectionValvesSyringe/septum
5. Analytical Column
A. Stationary phase• Liquid on solid surface
High Performance Liquid Chromatography
Bonded phase packings
R: C8
C18
R: (CH2)n NH2
(CH2)nCN
Reverse Phase vs. Normal Phase
Normal Phase Chromatography
sp: polar
mp: less polar
Increase solvent strength: add more polar solvent
Reverse Phase Chromatography sp: nonpolar mp: more polar Increase solvent strength: add more nonpolar solvent
High Performance Liquid Chromatography
General Elution Problem in Chromatography
Much shorter time
High Performance Liquid Chromatography
DetectorsSensitiveLinear responseSmall volume cellsInsensitive to changes in T, solvent
A. UV-Vis
Must absorb radiation
B. Refractive Index
Universal
Less sensitive
T, P solvent sensitive
C. ElectrochemicalMust be able to be
reduced/oxidizedSelective
D. FluorescenceVery sensitiveSelectiveDerivatization
High Performance Liquid Chromatography
5. Detectors - Comparison
Detector Detection limits, ng
UV 0.1-1
RI 100-1000
Echem 0.01-1
Fluorescence 0.001-0.01
Qualitative and Quantitative Analysis
QuantitativePeak heightPeak areaCalibration with
standardsInternal
standard method
QualitativeLimited # of componentsAbsence of componentUse hyphenated
techniques
From Skoog, West, Holler,