Salinometry

Salinometry is the measurement of salinity, the concentration of dissolved salts in a solution, most commonly seawater or freshwater samples. It is essential in oceanography, hydrology, climatology, and various industrial processes, and encompasses a range of instruments and techniques used to estimate salt content.

The most widely used method in marine science is conductivity-based salinometry. A salinity sensor measures the electrical conductivity of the sample, which increases with higher salt content. Temperature is measured and used to correct the conductivity reading, because conductivity is temperature dependent. The resulting value is converted to a salinity measure on a standard scale, typically the Practical Salinity Scale (PSS-78) or the TEOS-10 framework that distinguishes Absolute Salinity from Practical Salinity.

Other methods include refractometry, which relates the refractive index of a solution to its salinity, and densitometry, which uses density changes due to dissolved solids to infer salinity. Historically, chlorinity titration was used to estimate salinity through chemical analysis, and while less common today, it laid the groundwork for modern salinity scales.

Units and scales: Practical salinity is presented as psu (practical salinity units), a dimensionless quantity roughly equivalent to grams of dissolved salts per kilogram of seawater, with typical seawater near 35 psu. Absolute Salinity, used in TEOS-10, expresses salinity in more physically defined terms.

Applications and considerations: Salinometry enables real-time oceanographic profiling, climate studies, desalination and water-treatment processes, and quality control in the food and beverage industry. Accuracy depends on proper calibration, temperature compensation, prevention of sample contamination, and routine instrument maintenance. In low-salinity waters, measurements can be more challenging due to low conductivity.