Small-angle X-ray scattering for macromolecules in solution is now widely used in structural biology and complement high-resolution structure determination obtained by X-ray crystallography or NMR. In the context of third-generation synchrotron sources, this increasing interest leads to developments in sample environments and automation.
The presence of an online puriﬁcation system is justiﬁed by the need for sample monodispersity. A combined system, unique in Europe, including an auto-sampler robot and online high-performance liquid chromatography (HPLC) has been developed and optimized at the SWING beamline of Synchrotron SOLEIL. In the sample changer mode, a few microlitres of sample can be injected between two air bubbles and circulated at a controlled speed of typically 40 µl per min. About 12 samples per hour can be measured in this mode by remote controlling the sample injections. In the HPLC mode, an initially polydisperse sample can be separated into each of its components before immediate data acquisition. The thermostated capillary flow through sample cell offers a visualization control and online UV–Vis absorption monitoring.
For kinetic experiments, a BioLogic SFM400 Stopped-Flow device equipped with a Quartz capillary cell is also available.
Concerning data reduction and first analysis, SOLEIL has developed a software application called Foxtrot especially dedicated to objects in solution. Foxtrot allows for 2D data reduction into 1D files, computation of absolute intensity and determination of radius of gyration and absolute 0-angle intensity as a function of frame number. This last feature is particularly attractive in combination with the HPLC and Stopped-Flow devices. The reduced data are available both through Hierarchical Data Format files, under the NeXus standard, and ASCII files. The application Foxtrot can be downloaded by our users for further data treatment in their home laboratory.