The principle of the device is based on the measurement of the critical angle (the angle of total internal reflection) and the calculation of the refractive index

Potentiometric pH meters measure the voltage between two electrodes and display the result converted into the corresponding pH value. They comprise a simple electronic amplifier and a pair of electrodes, or alternatively a combination electrode, and some form of display calibrated in pH units.

An ion-selective electrode (ISE) is an example of an electrochemical sensor utilizing the principle of potentiometry, or measurement of the cell potential (i.e., ISE against a standard reference electrode) at near-zero current.

The principle of Karl Fischer titration is based on the oxidation reaction between iodine and sulphur dioxide. Water reacts with iodine and sulphur dioxide to form sulphur trioxide and hydrogen iodide. An endpoint is reached when all the water is consumed.

Spectrophotometry measures the amount of light that a sample absorbs at a particular wavelength.

Polarimetry measures the rotation of polarized light as it passes through an optically active fluid. The measured rotation can be used to calculate the value of solution concentrations;especially substances such as sugars, peptides and volatile oils. polarimeter consists of a polarized light source, an analyzer, a graduated circle to measure the rotation angle, and sample tubes

Conductivity is the ability of a material to conduct electric current. The principle by which instruments measure conductivity is simple two plates are placed in the sample, a potential is applied across the plates (normally a sine wave voltage), and the current that passes through the solution is measured. Conductivity (G), the inverse of resistivity (R), is determined from the voltage and current values according to Ohm's law.

it is a controlled flame test with the intensity of the flame color quantified by photoelectric circuitry. The intensity of the color will depend on the energy that had been absorbed by the atoms that was sufficient to vaporise them. The sample is introduced to the flame at a constant rate.

The Kjeldahl method is a method for determining the total nitrogen in a compound or mixture. Digestion of samples with concentrated sulfuric acid under catalyst conditions converts organic nitrogen to inorganic ammonium salts, and then converts ammonium salts to ammonia under alkaline conditions. It is distilled with water vapor and absorbed by excess boric acid solution, and then titrated with standard hydrochloric acid to calculate the amount of nitrogen in the sample.