Patrick Endres discusses how light scattering technology with high sensitivity facilitates the analysis of synthetic and biopolymers
The multi-angle light scattering (MALS) technique has become the standard to determine molecular weight (MW) and size – measured in radius of gyration (Rg) of proteins, biopolymers, synthetic polymers and polysaccharides.
In contrast to some conventional light scattering detectors already available on the market, a new MALS detector – Tosoh LenS3 – is capable of directly determining absolute molecular weight and Rg without extrapolation. This is achieved by combining an extreme low angle (LALS – 10°) and an extreme high angle (HALS – 170°) with a right angle (RALS – 90°) to form a three-angle MALS detector (Fig.1.).
As opposed to a conventional flow cell, the new extended “flow chamber” allows maximum interaction of the incident beam with the molecules of interest, resulting in significantly higher scattering intensity. Coupling this smart design feature with a lower laser wavelength, 514nm, as opposed to a typical 660nm, LenS3 offers excellent detection sensitivity. As well as this, in contrast to a typical optical flow cell composed of a glass-like material, the new flow chamber is made with PEEK, a non-refractive material, substantially reducing the destructive stray-light effect in light scattering detection. Hence, the quality and stability of signals at extreme angles (LALS and HALS) are significantly improved.
Measurement at such angles on the detector allows MW determination as low as 200 Da (Fig. 2).
Addressing other limitations
In addition, the LenS3 addresses the two major limitations of the Zimm method by a new angular dependence calculation using the “angular dissymmetry plot”. Thanks to this new underlying theory, the strategic positions of the angles, and the superior sensitivity, LenS3 can now determine Rg values at much lower size range compared to some existing MALS instruments without requiring solute concentration or refractive index increment (dn/dc) values. Even with many more angles of observation, conventional detectors can only determine Rg down to 10nm. With the LenS3 detector, determination of Rg as low as 2nm is now possible.
In summary, the LenS3 MALS detector is a novel innovation in light scattering technology. The new detector integrates the best of both MALS and LALS concepts to create a new paradigm in light scattering detection.
Patrick endres is a senior lab specialist with Tosoh Bioscience