Soil-chemical processes studied by the stopped-flow technique with electrical-conductivity detection

The stopped-flow technique is a method to study the kinetics of chemical reactions at a time scale of milliseconds and seconds. We reviewed the application of the stopped-flow technique with electrical-conductivity detection to soil-chemical processes. The technique can provide rates and activation energies of reactions, in which charged species are consumed or generated, which take place in solution and, with some limitations, in suspension, that is, at the solid–liquid interface. It is therefore a valuable tool for gaining mechanistic insights, which are usually tested with additional approaches such as batch experiments and spectroscopic methods. Meaningful stopped-flow experiments require careful consideration of pre-conditions regarding the reaction, sample and measurement conditions. We have elaborated these preconditions, together with fundamentals of data acquisition and analysis, and the possibilities of the technique to disentangle complex chemical reactions with a series of stopped-flow experiments. Although the stopped-flow technique with conductivity detection is not a widely used method in soil chemistry research, we see great potential for its application, particularly in sorption processes of charged species such as organic anions or metal cations interacting with soil minerals or mineral-organic associations. Stopped-flow analyses of these processes can help to identify the number of successive processes and can thus elucidate the rapid reaction kinetics, including the rates and energies. Processes can thus be identified and parameterised and implemented in soil-chemical models.