Figure 20.

(a) Camera-assisted titration of ammonia using bromocresol green. NH₃ is dissolved in the gas-flow reactor inside a temperature-controlled bath, and then mixed with varying proportions of acid. (b) The point of neutralisation is observed by a colour change from yellow to blue: The camera collects images which are analysed by a computer. The image is split into its “blue” and “yellow” components and the relative proportions compared. (A pixel is considered to be blue if (2r – 2b > 140); and yellow if (2b – 2r > 140) where b and r are the blue and red values of the pixel, respectively). The concentration of NH₃ dissolved within the reactor at each bath temperature can then be calculated from the pH at which the stream is neutralised.