Size-exclusion chromatography–small-angle neutron scattering system optimized for an instrument with medium neutron flux

Biomacromolecular solutions inevitably contain impurities in addition to the target biomacromolecules. This has been a major obstacle to achieving high-precision solution scattering measurements. To overcome this problem, small-angle X-ray scattering (SAXS) coupled with size-exclusion chromatography (SEC-SAXS) has been developed. This method involves injecting the solution eluted by SEC directly into a measurement cell and conducting SAXS measurements during the elution of the target biomacromolecule. This technique has resulted in a paradigm shift in biomacromolecule solution scattering. Currently, the application of the SEC-SAXS system to small-angle neutron scattering (SANS) is being advanced. However, since the target biomacro-mol-ecules in the sample solution are not only purified but also diluted by SEC and pass through the sample cell in a short time, this method is being implemented in SANS instruments at high neutron flux. Here, we developed a new type of SEC-SANS system that can operate effectively with a SANS instrument at medium neutron flux. Its key innovation is the design and optimization of a dedicated flow path that allows for the storage of only the target biomolecules eluted from SEC in the sample cell. This innovation enables long-duration measurements, termed the 'stopping mode', for SEC samples. Consequently, this method allows for acquiring high-precision solution scattering data for target biomacromol-ecules, enabling SEC-SANS measurements even with SANS instruments at medium neutron flux.