Stopped-flow data capture

In addition to the continuous-flow reactors, we developed a stopped-flow apparatus to study slow reactions of the NO3 radical. In this apparatus, a series of solenoid valves is used to divert and isolate a flow of gas that contains the reaction mixture. These valves were designed and fabricated in this laboratory by the PI, and ensure that only glass is in contact with the flow. Concentrations of NO3 are then followed as a function of time after the flow is cut off, the data being captured by computer. Figure 1 shows the apparatus in schematic form, while Fig. 2 illustrates decay curves for [NO3] in the absence and presence of C2H4. 

Rgure 4 Analysis of time course to measure the flow time and the dead time. The first 10 ms of the traces In Figure 3 are shown as individual data points. The solid lines are the exponential fits to the data extrapolated back to true time zero. The flow period is the flat initial portion of the curve and, in principle, may have any length and depends on the time between triggering data capture and the flow stopping. The dead time is the time between t = 0, given by the point of intersection of the cun/es, and when flow stops. In this experiment the dead time and flow period are approximately the same, but need not be so. 

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