Why is normalization of my MALS detector important for accurate molar mass and size measurements? - WKB319119
ENVIRONMENT
- DAWN
- microDAWN
- miniDAWN
- Wyatt multi-angle light scattering (MALS) detector
- ASTRA software
ANSWER
Normalization of a Wyatt MALS detector ensures accurate molar mass and size measurements by correcting for differences in angular sensitivity and geometry among its photodiodes. Each detector is calibrated against the 90° angle detector using sample-specific normalization coefficients. These coefficients are calculated using isotropic scatterers with known radii. Once normalized, variations in scattering intensity reflect only sample properties. This process improves the precision of radius of gyration and molar mass measurements.
ADDITIONAL INFORMATION
Why is normalization of my MALS detector important for accurate molar mass and size measurements?
The following video will go through step by step instructions on how to normalize your Wyatt multi-angle light scattering (MALS) detector. In addition, the video will also compare a Debye plot before and after a data file is updated with new normalization coefficients. The new normalization coefficients resulted in an increase in the R2 value for the first order polynomial and a decrease in the uncertainty of rms radius measurement. Overall, this video demonstrates why normalization is important to accurate molar mass and radius of gyration, Rg, measurements.
A Wyatt MALS detector can have up to 18 photodiodes and each photodiode has its own angular sensitivity to scattered light. These angular sensitivities, in combination with each detector’s geometric features, will affect the measured scattered light intensity differently. Correcting for differences in angular sensitivity and geometric effects will reduce error in molar mass and size measurements. In order to correct for these differences, normalization coefficients are used to relate each detector to the 90° angle detector. The 90° angle detector is calibrated in toluene and the calibration is independent of sample and solvent. Normalization coefficients are temperature and solvent specific and unlike the 90° detector, are calculated using sample analysis.
Ideally a sample that scatters light isotropically, with equal intensity in all directions, is used for normalization. Using an isotropic scatterer with a known radius allows ASTRA to calculate a set of coefficients so that each detectorttering intensity as the 90° detector. After normalization, differences in the light scattering intensity at each photodiode can be attributed solely to sample characteristics.
Wyatt has a list of recommended standards for normalization, which are also available at the polystyrene in toluene or THF, having an rms radius of about 5 nm. g/mol polysaccharide such as pullulan or dextran in water, or a PEO, also having a rms radius of about 5 nm.