An analytical methodology has four cascading levels: technique, method, procedure, and protocol.

A technique is a scientific principle that rationalizes a specific phenomenon through chemical measurements.

A method is the adaptation of a technique for analyzing a particular sample of interest.

A procedure is a set of directions to perform the analysis.

A protocol is the strict guidelines to be adhered to while detailing the procedure.

Analytical methods can be categorized into classical and instrumental.

In classical methods, the component of interest –the analyte– is separated from the rest of the sample-matrix via wet chemical processes like precipitation, extraction, or distillation.

Alternatively, instrumental methods probe the physical properties of an analyte, such as conductivity, electrode potential, light absorption or emission, and the mass-to-charge ratio.

Analytical method selection is determined by the requirements of equipment availability, accuracy, precision, sensitivity, selectivity, robustness, ruggedness, cost, analysis time, and the scale of operation.