It will explain and differentiate between the techniques and technologies used in SLS, MALS, RALS, and LALS. It assumes no prior knowledge of the light scattering theory or instrumentation and should be ideal for those new to light scattering and those looking to increase their knowledge in the area. The guide covers an introduction to the theory and background of molecular weight measurements by static light scattering. It is hoped that the information contained in here will help users to make an informed decision about the most appropriate light scattering technology to use.
SUMMARY
Static light scattering is a technique to measure the molecular weight using the relationship between the intensity of light scattered by a molecule and its molecular weight and size. These relationships are described by Rayleigh theory which states that the molecular weight of a molecule is proportional to the Rayleigh ratio of scattered light i.e. the ratio of scattered light intensity to incident light intensity. All static light scattering instruments detect the amount of light scattered by a sample to measure its molecular weight; however, as molecules grow in size, a second factor called angular dependence becomes significant. Angular dependence affects the intensity of scattered light and hence the calculated molecular weight. It must therefore be accounted for.• A RALS detector collects scattered light at 90°. It can measure molecular weight with high sensitivity for samples that scatter light isotropically i.e. equally in all directions; however it cannot measure molecular weight for anisotropic scatterers (those affected by angular dependence).
• A LALS detector collects scattered light at 7°. It can measure molecular weight for all molecules but has a lower signal-to-noise.
• By combining RALS and LALS detectors into a hybrid system the molecular weight of all samples can be measured while maximising signal-to-noise where required. It therefore offers the strengths of both LALS and RALS with none of their weaknesses.
• A MALS detector collects scattered light at many angles. This data is used to model the angular dependence to account for it in the molecular weight calculation. It can measure molecular weight for both isotropic and anisotropic scatterers and for anisotropic scatterers can also measure the radius of gyration.
• All static light scattered instruments must be calibrated before use. Calibration can either be performed using a molecular weight standard or a scattering standard and each has advantages and disadvantages that are described in the calibration section.
INTRODUCTION
Light scattering can be a confusing topic. There are a number of different techniques that come under the general heading of light scattering and a range of parameters that can be measured. The lines between these can become blurred, as some systems use more than one technique in a single instrument, so it is very easy to lose sight of the most important factors when considering which light scattering technology is right for your application. Static light scattering, also called classical light scattering, is a technique used to measure molecular weight and molecular radius of gyration. Within static light scattering, there are a number of different technologies with acronyms such as SLS, MALS, LALS and RALS and others. Each of these is subtly different and each has advantages and disadvantages. This white paper describes, in some detail, the principles and theories behind static light scattering. The theory, technique and the different technologies are described and compared. By reading this white paper, you should be able to understand the background to these measurements and make an informed choice on the most appropriate solution for your application. Each section provides a great deal of detail, but begins with a few key points to summarise the information contained so you can decide whether you need to read the detail in that section.>> Download the full White Paper as PDF
Malvern provides the materials and biophysical characterization technology and expertise that enables scientists and engineers to investigate, understand and control the properties of dispersed systems. These systems range from proteins and polymers in solution, particle and nanoparticle suspensions and emulsions, through to sprays and aerosols, industrial bulk powders and high concentration slurries. Used at all stages of research, development and manufacturing, Malvern’s instruments provide critical information that helps accelerate research and product development, enhance and maintain product quality and optimize process efficiency. Our products reflect Malvern’s drive to exploit the latest technological innovations. They are used by both industry and academia, in sectors ranging from pharmaceuticals and biopharmaceuticals to bulk chemicals, cement, plastics and polymers, energy and the environment. Malvern systems are used to measure particle size, particle shape, zeta potential, protein charge, molecular weight, mass, size and conformation, rheological properties and for chemical identification, advancing the understanding of dispersed systems across many different industries and applications. www.malvern.com Material relationships http://www.malvern.com/en/
Newsletters
Receive the latest analytical science news, personalities, education, and career development – weekly to your inbox.
