Question

How does one calibrate a stopped-flow apparatus? How do we know whether or not to trust a measurement from the stopped-flow method?

Answer 1

Solution:

Calibration of stopped flow apparatus:

The stopped-flow technique allows for the evaluation of solution-based kinetics on a milliseconds timescale with a very small volume of reactants used. The improved calibration is based on a test reaction generally used for dead-time determination. Hence need to obtained from the classical evaluation with the software provided for the runs carried out at set atm pressure. It is emphasized that data is created on the same database, which resulted in absorbance unit average deviation using the correct model for the evaluation, therefore the measurements are precise. It should be mentioned, moreover, that the usual evaluation presented is theoretically equivalent with Model 1 (First-order, no integration), which will resulted in an almost acceptable absorbance unit average deviation. The dierence is that the exponential curves are individually used to determine the points i.e. the constraint that the initial absorbances should be the same is not (and cannot be) taken into account. Therefore, more than half of the points must be removed to obtain an acceptable straight line. The fitted line presented in obtained figure will be calculated by omitting the three slowest and the six fastest runs. The calculated dead-time will be acceptable agreement with the value calculated from Model 1 at set atm pressure. In spite of this, Figure obtained may result in a misleading conclusion that the given instrument should not be used.

Using above calibration method we can trust for the calculations for stopped-flow method. If the calibrated values matched with set model pressure conditions then the instrument is in good condition and ready to use.