Total dissolved solids (TDS) meters: which measurements can be used to monitor mineral content and salinity?

From drinking water monitoring to food-grade brines, via pharmaceutical processes and the environment, dissolved-salt analysers keep you within spec. Depending on your sample matrices and targets, they quantify salinity and TDS (total dissolved solids) via conductivity, measure chloride ions directly (ISE, titration), or use refractometry for rapid checks. IP67 handheld and benchtop instruments combine ATC, traceable calibration and data logging for uncompromising data quality.

What are the different types of sensors for dissolved salts, and how do they work?

By “dissolved salt”, we mainly mean NaCl and the major ions. Three approaches dominate, complemented by titration.

• Conductivity meters / salinometers / TDS meters: they measure electrical conductivity (µS/cm to mS/cm). 2-electrode cells cover low to medium salinities; 4-electrode designs limit polarisation for wider ranges; inductive sensors excel in very saline, fouling media. Choose a cell constant K=0.1 / 1.0 / 10 cm?¹ to match the range, ATC is essential, and calibrate against KCl standards. Conversion to TDS and salinity (PSU) is derived from conductivity using factors (typically 0.5–0.7 depending on the matrix).

• Chloride ISE probes: they specifically measure Cl? ions from mg/L to g/L with added ISA (ionic strength adjuster) and multipoint calibration. Beware of interferences (Br?, I?). Ideal when chloride must be measured separately from the rest of the salts.

• Refractometers: the refractive index varies with salt concentration. Fast for food brines and salt baths, with temperature compensation. Prefer dedicated NaCl scales; sugary or fatty matrices can bias the reading.

• Argentimetric titration (Mohr, potentiometric): add AgNO? to determine chloride precisely, even in coloured/turbid samples (potentiometric detection of the equivalence point). The reference for accuracy and regulatory compliance.

Selection criteria: measurement range, accuracy, wetted materials (stainless steel, graphite, PTFE) according to chemistry and temperature, management of ATC, traceability of the calibration, interface (portable, benchtop, in-line) and maintenance (mild acid cleaning, anti-fouling, guided calibrations).

Type	Principle	Applications
Conductivity meter / Salinometer	Measurement of conductivity, conversion to TDS/salinity	Water, processes, brines, aquaculture
Chloride ISE probe	Ion-selective potential for Cl? ions	Chlorides in pharma, environment, corrosion
NaCl refractometer	Refractive index vs concentration	Food brines, salt baths, rapid checks
Argentimetric titrator	AgNO? titration (Mohr/potentiometric)	Metrological reference, compliance

In which applications is a salinity meter used?

• Water & environment : salinity monitoring, saltwater intrusion control, monitoring reverse osmosis and softening, compliance with discharge limits.
• Food industry : formulation and control of brines, cheese making, cured meats, fish, pickles; sensory consistency and microbiological safety.
• Pharmaceutical & biotech : control of chlorides and ionic strength in purified waters, buffers, WFI (particle-free); process and cleaning control.
• Cosmetics & chemicals : bath monitoring, salt-containing surfactants, electrolytes; corrosion prevention and formulation stability.
• Aquaculture & aquarium keeping : salinity adjustment for animal welfare and system health.

Available types of sensors for dissolved salts

Dissolved salt detector

Frequently asked questions about salinity meters

What is the difference between conductivity, TDS and salinity?
Conductivity is measured directly. TDS and salinity are calculated using matrix- and temperature-dependent factors/algorithms.

How do I choose the cell constant (K) of a conductivity meter?
K=0.1 for low conductivities, K=1 for most waters, K=10 for highly saline brines or high-concentration in-line measurements.

Does a chloride ISE replace a salinometer?
No. The ISE measures Cl? specifically. The salinometer reflects all conducting ions. Choose according to your criterion (chloride vs total salts).

How important is temperature compensation (ATC)?
Essential: conductivity changes by ~2 %/°C. ATC normalises to 25 °C, ensuring comparability and compliance with methods.

Is the refractometer suitable for sugary matrices?
Use caution: sugars alter the refractive index. Use a dedicated NaCl scale, verify matrix effects, or prefer conductivity/titration.

What are good calibration and maintenance practices?
Calibrate regularly (KCl/NaCl), rinse with deionised water, clean gently (mild acid for scale), check ATC and log the data.