Salinity measurement could be determined through several approaches including the refractive index using refractometers. The principle of the refractive index is based on the light refraction through liquids; the more dissolved solids in water, the slower light travels through it. The amount of bending (refraction) is related to how much salt is dissolved in the water.
Refractometers which are handheld devices measure the difference in light refraction between solutions. The amount of salt dissolved in a given quantity of water changes its refractive index, allowing water salinity to be measured optically.
Calibration: The calibration of the refractometer is done through placing two to three drops of distilled water on the prism before closing the cover plate and start reading. If the refractometer reads zero, no calibration will be needed. If the refractometer reads other than zero, the calibration screw should be turned the scale until it reads “0” and hence the calibration is complete.
Measurement: To check water salinity using a refractometer, 2-3 drops of water are placed on the optical prism of the held-level refractometer. Afterwards, the reading of the sharp-looked numbers that correspond with separating line between the two fields (light/dark) of the meter would measure the salinity in gram/liter of the water sample.
