This project deals with fabrication of a stopped-flow device for time-resolved XAFS experiments. We have constructed a compact stopped-flow device for use at the BioCAT beamline. Two drive syringes and a stop syringe are embedded in a support frame for structural and thermal stability. Solenoid valves are connected to the syringes which have a fast response time. A Berger ball mixer, which has a mixing volume of 4 ml is directly mounted on the sample holder to further limit the dead volume. The total volume of the sample holder is 70 ml. The system is enclosed in a shroud with mylar windows. The temperature is controlled by regulating the flow of cold nitrogen helium gas into the system and the current of tape-heaters on the supporting frame. Test shows that temperature can be controlled within a few degrees for several hours. Automated driving systems were designed and fabricated. Servo-motors are used to provide an accurate and fast repetitive sample delivery. The separate motor drives for the stop syringe and driving syringes can satisfy these requirements and yet are versatile for different mixing proportions. A PC will be used to control the drive and stop syringes, and the solenoid valves. Initial tests of the stopped-flow are underway. One of the prerequisites of the device is its low level of metal contamination. The impurity of the system is found to be equivalent to 50 mM at Fe and Zn edges. The performance of the stopped-flow will be tested first using a simple metal ion reaction, such as the mixing of cyanide and ascorbate at low pH. The system will also be tested for biological reactions.
