In this section, the basics of experimental designs are introduced. Many definitions are given to introduce the most usual nomenclature and to avoid some common misconceptions. A practical and easy‐to‐follow approach was preferred instead of a more formal one, and literature references are given for more advanced or interested readers.

An ‘experiment’ is just a test or series of tests. Experiments are performed in all scientific disciplines and are an important part of the way we learn about how systems and processes work. The validity of the conclusions that are drawn from an experiment depends to a large extent on how the experiment was conducted. Therefore, the design of experiments plays a major role in the eventual solution of the problem that initially motivated the experiment and, as a consequence, what it is currently understood by ‘experimental design’ is an important tool for analytical chemists who are interested in improving the performance of an analytical procedure. The term ‘performance’ may be rather ambiguous although, in general, we relate it to an analytical property we are interested such as recovery, signal‐to‐noise ratio, uncertainty and robustness, and we assume that this property is influenced by an undefined number of experimental conditions such as pH, reagent concentrations, analytical method, instrumental conditions, analyst and so forth.