The color of every object we see is determined by a process of absorption and emission of electromagnetic radiation (light) by the molecules of which it is made.

Colorimetric analysis is based on the principle that many substances react with each other and form a product whose color is determined by the concentration of the substance to be measured.

When a substance is exposed to a beam of light of intensity lo a portion of the radiation is absorbed by the substance's molecules, and a radiation of intensity I lower than lo is emitted.

The photoelectric cell collects the radiation I emitted by the sample and converts it into an electric current, producing a potential in the mV range.

The microprocessor uses this potential to convert the incoming value into the desired measure unit and to display it on the LCD. In fact, the preparation of the solution to be measured occurs under standard conditions, which are memorized in the meter's microprocessor in the form of a calibration curve. This curve is the reference base for each measurement. In this way, it is possible to dose unknown concentrations of the sample and induce the colorimetric reaction, and thus obtain the mV related to the emitted intensity I (the color of the sample). Then by using the calibration curve, it is possible to determine the concentration of the sample that corresponds to the mV value.

The measurement process is done in two phases: setting the meter to zero, and the actual measurement. The first phase consists of collecting a sample of the substance to be measured in the calibration cuvette which is inserted into the meter. In this way, a reference value is set up, so that it is possible to establish how much the color of the substance has varied in the next phase, using the sample in the measuring cuvette that has been treated with the reagent.

The cuvette has a very important role because it is an optical element, and thus requires particular attention. First of all, it is important that both the measurement and the calibration cuvettes are optically identical to provide the same measurement conditions. It is also necessary that the cuvette's surfaces are not scratched and are clean, in order to avoid measurement interferences due to unwanted reflection and absorption of light. Furthermore, in order to maintain the same conditions during the resetting and the measuring phases, it is necessary to close the cuvettes if they contain volatile substances. The cuvettes used with the colorimeters have been designed to avoid any external light contamination when inserted into the meter.