Salinity is a measurement that has different meanings in different industries. Overall it is a measurement of salts in water. Salts can be measured by electrolytic conductivity (EC), refractometry, titration of chloride, or specifically for sodium chloride using a sodium Ion-Selective Electrode (ISE).
Salinity measurements can be broken down into two major forms. Those that are for oceanographic studies for seawater salinity and those for food or brine solutions in which there is a weight/weight or weight/volume relationship.
There are meters that offer seawater salinity scales. The seawater salinity scales are Practical Salinity Scale (PSU); 1978, Percent Scale (%); and Natural Seawater Scale(g/L); 1966.
Practical Salinity Units (PSU) - This is a practical scale based on the precise measurement of the electrical conductivity of a solution with a known salinity range. The relationship derived from the scale relates salinity, conductivity, temperature, and pressure and use a solution with a salinity of 35 ‰ as datum point. This is taken to have a conductivity of 42.914 mS/cm of 15 °C at standard atmospheric pressure.
NaCl % Percent Scale – The NaCl % scale is an older salinity scale used for seawater salinity. In this scale 100% salinity is equivalent to roughly 10% solids.
Natural Sea Water Scale (UNESCO 1966) - Salinity is based upon a conductivity ratio of sample to “standard seawater” at 15 oC and 42.914mS/cm being the corresponding conductivity of KCl solution containing a mass of 32.4356 g KCl / 1 Kg solution.
Salinity other than Seawater
Brine solutions and salinity as sodium chloride use a different scale than seawater. Salinity is expressed in a weight/weight (i.e. 10g/100g) or weight/volume (i.e. 10g/100ml). This is not the same as the NaCl % scale found on some conductivity meters. With that scale 100% NaCl is equivalent to Atlantic Seawater that is approximately 35 ppt (3.5 g/100 ml). Titrators and meters are available to measure salinity as w/w or w/v.
Hanna Instruments offers a variety of technologies to measure Salinity. Potentiometric measurements with portable and benchtop pH/ISE meters are available to use with the sodium ISE for direct ion concentration measurements. Potentiometric titrations systems are available for either direct measurement using the ISE mode or for performing a salt titration. Refractometers, testers, and chemical test kits are also available.