Common Detectors for GPC/SEC Applications
A brief overview of the detectors used in GPC/SEC Chromatography with the purpose of showing detection principles and differences of the instruments now commercially available.
Detector Classes
Concentration Detectors (RI, UV, IR)
Molar Mass Sensitive Detectors (Viscometer, SLS, DLS)
Unspecific Detectors (ELSD, Corona)
Concentration Detectors
Refractive Index Detector (RI)
For Polychromatic light source: 
For Monochromatic light source: 
Classic UV Detector
Signal Response: 
Photodiode Array detector (PDA)
Signal Response: 
Comparison of Concentration Detectors
Polychromatic RI
Wide dynamic range, high linearity, good sensitivity
No dn/dc information
Monochromatic RI
Wide dynamic range, high linearity, good sensitivity and dn/dc values.
Classic UV
Highest sensitivity and selectivity.
Limited dynamic range
PDA
High sensitivity, delivers full absorbance Spectra
Limited dynamic range, selectivity not fully defined
Viscometers
Single Capillary (Ouano)
Signal: 
Where: K = Capillary Constant, Q = Flow Rate, eta = Viscosity
Differential Viscometer (Haney)
Signal: 
Differential Viscometer (Bures)
Combined Viscometer / RI (Bures)
External vs. Internal combination Viscometer / RI
Comparison of Viscometers
Single Capillary
Huge dynamic range, intrinsically linear, simple combination.
Poor sensitivity, highly sensitive to temperature and pump pulses.
Haney Bridge
High sensitivity, little influence of temperature or pump pulses.
Shows "Breakthrough" after sample peak, complex combination.
Bures Bridge
High sensitivity, little influence of temperature or pump pulses, no "Breakthrough" after sample peak, low band broadening.
Complex combination.
Combined Bures Viscometer/RI
Highest sensitivity, simple combination with other detectors
Static Light Scattering Detectors
Single Angle SLS Detectors
Multi Angle Light Scattering (Wyatt)
Multi Angle Light Scattering (Reed)
Comparison of SLS Detectors
Small Angle
Limited sensitivity, no extrapolation possible thus no Rg information, obsolete.
Right Angle SLS (RALLS)
Needs Viscometer and RI to obtain MW, no Rg information, questionable method.
MALLS (Wyatt)
Excellent sensitivity and linearity. Non optimal Flowpath.
MALLS (Reed)
Excellent sensitivity. Optimal Flowpath.
Unspecific Detectors
Evaporative Light Scattering detector (ELSD)
Solvent is separated from solute via evaporation, scattering of solute is then detected.
Response (Signal) is substance dependent, individual calibration necessary. Limited dynamic range. Good sensitivity.
Corona
Uses the "Corona" effect. Solvent is separated from solute via evaporation. The solute is then "wrapped" in a
layer of ionized nitrogen and detected.
Common Detector Combinations
UV-polyRI
Co-Polymer composition analysis
RI-Viscometer
MW via universal calibration, MHS-coefficients, Rh, Branching
RI-MALS
"Absolute" MW, Rg
RI-Viscometer-Single Angle SLS
MW via "Triple detection"
RI-Viscometer-MALS
Absolute MW, Structure analysis, Branching
Practical Aspects of Combinations
