SEC-MALS analysis

What is SEC-MALS used for?

SEC-MALS is primarily used to determine the spread of different molecular weights in a solution and is therefore mostly used with large macromolecules. These might be in the form of biomolecules, such as proteins, or high-molar-weight polymers.

SEC-MALS helps determine molecule sizes, shapes, and conformations, making it an essential technique in the biopharmaceutical and medical fields. The method is also used in polymer characterization to determine the various molecular weights of the polymer chains, which gives insight into the progression of reactions and provides information on how molecular weight impacts the physical properties and applications of industrial polymers.

How does SEC-MALS analysis work?

SEC-MALS analysis begins by passing the solution through a chromatography column, which acts as a molecular filter and hinders the movement of the solution. This causes the individual components in the solution to be separated according to various factors, such as their physical size and molecular weight.

As the components leave the column, they are exposed to a laser. Upon passing through the sample, the light from the laser is scattered and picked up by a detector. The intensity of the scattered light is directly linked to the weight of the molecule, and can therefore be used to accurately determine the different spreads of molecular weights in the molecules. Through further calculations, this data can also provide information on things like levels of branching, conformation, and conjugation in the molecule.

Sample requirements and preparation

SEC-MALS is performed in a solution; therefore, any solid sample matter is dissolved in a suitable solvent appropriate for the column. Some samples, especially biomolecules, may need an additional buffer solution, which must be matched with the column. Large particulates can block the column, so solutions may need to be filtered to ensure they are free of solid debris before analysis.

Advantages and limitations of SEC-MALS analysis

The main advantage of SEC-MALS is that it can interpret a wide range of different molecular masses, which means it can be used to analyze even some of the largest macromolecules. This makes it stand out compared to conventional techniques, which historically struggle with very large molecules. It can also be used to provide additional information, such as conjugation, levels of branching, and stoichiometry, all things that cannot be measured with SEC alone.

The main limitation of SEC-MALS is its inability to easily distinguish between molecules of the same size. This makes it difficult to analyze some oligomers or isomers with very similar sizes. Furthermore, to achieve the best separation it is sometimes necessary to run several columns in succession to determine the best flow characteristics and calibrate the system accordingly. This trial-and-error operational style can sometimes lead to relatively long processing times.

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