On a precipitation curve, where does maximal precipitation occur?

Maximal precipitation occurs in the zone of equivalence. This zone represents the optimal point at which the concentrations of antigen and antibody are balanced, allowing for the formation of the largest visible precipitate. In this region, the number of antigen-antibody complexes formed reaches its peak, resulting in the most effective precipitation reaction.

In the zone of antigen excess, there is an excess of antigen relative to the antibody, which can lead to fewer available binding sites for effective complex formation, thus resulting in less precipitation. Conversely, in the zone of antibody excess, the opposite is true; here, there may be more antibodies than antigens, which can also limit the formation of precipitate. Lastly, the zone of no precipitation indicates conditions where antigen and antibody do not adequately interact or the concentrations are below levels necessary for precipitate formation, resulting in no visible precipitate at all.