3.9 KiB
| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Absolute molar mass | 2/2 | https://en.wikipedia.org/wiki/Absolute_molar_mass | reference | science, encyclopedia | 2026-05-05T10:51:41.203455+00:00 | kb-cron |
== Applications == Light scattering measurements can be applied to synthetic polymers, proteins, pharmaceuticals and particles such as liposomes, micelles, and encapsulated proteins. Measurements can be made in one of two modes which are un-fractionated (batch mode) or in continuous flow mode (with SEC, HPLC or any other flow fractionation method). Batch mode experiments can be performed either by injecting a sample into a flow cell with a syringe or with the use of discrete vials. These measurements are most often used to measure timed events like antibody-antigen reactions or protein assembly. Batch mode measurements can also be used to determine the second virial coefficient (A2), a value that gives a measure of the likelihood of crystallization or aggregation in a given solvent. Continuous flow experiments can be used to study material eluting from virtually any source. More conventionally, the detectors are coupled to a variety of different chromatographic separation systems. The ability to determine the mass and size of the materials eluting then combines the advantage of the separation system with an absolute measurement of the mass and size of the species eluting. The addition of an SLS detector coupled downstream to a chromatographic system allows the utility of SEC or similar separation combined with the advantage of an absolute detection method. The light scattering data is purely dependent on the light scattering signal times the concentration; the elution time is irrelevant and the separation can be changed for different samples without recalibration. In addition, a non-size separation method such as HPLC or IC can also be used. As the light scattering detector is mass dependent, it becomes more sensitive as the molar mass increases. Thus it is an excellent tool for detecting aggregation. The higher the aggregation number, the more sensitive the detector becomes.
== Low-angle (laser)-light scattering (LALS) method == LALS measurements are measuring at a very low angle where the scattering vector is almost zero. LALS does not need any model to fit the angular dependence and hence is giving more reliable molecular weights measurements for large molecules. LALS alone does not give any indication of the root mean square radius.
== Multi-angle (laser)-light scattering (MALS) method == MALS measurements work by calculating the amount of light scattered at each angle detected. The calculation is based on the intensity of light measured and the quantum efficiency of each detector. Then a model is used to approximate the intensity of light scattered at zero angle. The zero angle light scattered is then related to the molar mass. As previously noted, the MALS detector can also provide information about the size of the molecule. This information is the Root Mean Square radius of the molecule (RMS or Rg). This is different from the Rh mentioned above who is taking the hydration layer into account. The purely mathematical root mean square radius is defined as the radii making up the molecule multiplied by the mass at that radius.
== Bibliography == A. Einstein, Ann. Phys. 33 (1910), 1275 C.V. Raman, Indian J. Phys. 2 (1927), 1 P.Debye, J. Appl. Phys. 15 (1944), 338 B.H. Zimm, J. Chem. Phys. 13 (1945), 141 B.H. Zimm, J. Chem. Phys. 16 (1948), 1093 B.H. Zimm, R.S. Stein and P. Dotty, Pol. Bull. 1,(1945), 90 M. Fixman, J. Chem. Phys. 23 (1955), 2074 A.C. Ouano and W. Kaye J. Poly. Sci. A1(12) (1974), 1151 Z. Grubisic, P. Rempp, and H. Benoit, J. Polym. Sci., 5 (1967), 753 Flow Through MALS detector, DLS 800, Science Spectrum Inc. P.J. Wyatt, C. Jackson and G.K. Wyatt Am. Lab 20(6) (1988), 86 P.J. Wyatt, D. L. Hicks, C. Jackson and G.K. Wyatt Am. Lab. 20(6) (1988), 106 C. Jackson, L.M. Nilsson and P.J. Wyatt J. Appl. Poly. Sci. 43 (1989), 99