ABSTRACT
About half of the identification tests are based on a methodology in which a selective chemical reaction performed on the substance to be examined yields a colored entity or even a colored precipitate that is directly recognizable as positive. These reactions are most commonly referred to as colorimetric reactions, although the name is also incorrectly used for photometric and spectrophotometric determinations. Historically in a photometric analysis, an unknown sample is compared to a series of standards of known concentrations using a natural light photometer, whereas spectrophotometry uses a UVvisible spectrophotometer with monochromatic light. In colorimetric determinations, on the contrary, samples and standards are compared and judged visually.
