3 The chemistry of colourimetric tests
In Section 2, the general approach was to add certain reagents to water which either changed colour on a strip or caused the sample to take on a degree of colouration itself.
So far though, you've concentrated on the hardware involved. Now, you will look at four of the parameters listed in Section 1.3 (ammonia, nitrate, sulfate and chemical oxygen demand), investigate a little about why their measurement is important and look at some of the chemistry exploited in colourimetric test kits (test strips, colour comparators or using photometric detection). You'll see that the reactions are based on standard reference methods, often dating from bygone days.