Anoxic SAXS

Anoxic SAXS (anSAXS) allows samples to be prepared and loaded within an anoxic chamber (<30 ppm O₂), which is directly connected to the X-ray sample cell, keeping samples and buffers fully anoxic through an experiment. Users can perform both batch and SEC-coupled SAXS, with the ability to spin down samples in a refrigerated centrifuge and collect UV-vis spectra anoxically. An in-line UV-vis cell (Avantes spectrophotometer) can be added to monitor the samples before or after the X-ray cell in real-time. A time series and full spectrum can be collected at any point during  sample elution.

AnSAXS samples can be shipped to CHESS or brought to the beamline frozen and thawed in the anoxic chamber. Sample and buffer considerations are the same as with conventional batch SAXS and SEC-SAXS. If planning to prepare buffer on site, house nitrogen is available for buffer sparging to reduce dissolved oxygen. Sample concentrations for anSAXS experiments are like that of conventional batch SAXS and SEC-SAXS, however, components that will be used during the experiment, such as centrifugal concentrators, buffer exchange columns, or other forms of non-standard tubing, must be arranged in advance to allow time for "degassing" within the chamber.

Temperature control is different for anSAXS than for conventional SAXS. Heat accumulation from mechanical components within the chamber has been minimized to a great extent, but the temperature within the chamber is often greater than the surrounding room. For batch anSAXS, the sample can remain on a cold block and at 4 °C within the refrigerated centrifuge until loading, when it is quickly transferred to the X-ray sample cell that is temperature controlled.