MALS can also be combined with ion-exchange chromatography (IEX-MALS) and reverse-phase chromatography (RPC-MALS), which-unlike SEC-cannot be calibrated to assign a molar mass to any specific retention time. When that does not work, either due to analyte-column interactions or simply analytes beyond the useful size range of SEC, MALS can be coupled to a different separation technique, field-flow fractionation. SEC-MALS is only effective if good separation is achieved on the SEC column. For more details on the theory of MALS, please see our MALS Theory page. In addition, the analyte’s dn/dc value (specific refractive index increment) in the mobile phase must be known or measured (this is easier than it sounds!). Most of the constants used to determine M and R g are related to system optical properties such as laser wavelength and solvent (mobile phase) refractive index. Radius of gyration, R g, is calculated from the slope.Molar mass, M, is calculated from the ratio of R(0) and the concentration.angle is fit to determine R(0) (the y-intersect at angle θ = 0) and the slope. The MALS detector incorporates between 3 and 18 photodiodes positioned at different angles θ relative to the laser beam to measure the scattered light function R(θ). In UHP-SEC-MALS, the peaks are much narrower, so data are collected at roughly 10 times per second. In SEC-MALS, the function of the SEC column is to separate solution components by hydrodynamic size (due to column interactions, some components may elute in the opposite order, and components of the same size may elute at different times).Īs each component passes through the detectors, its concentration and light scattering properties are measured every second or so. Dynamic & Electrophoretic Light Scattering.
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