Sodium occurs both naturally and as an additive in food products. It is commonly added to food products in the form of sodium chloride (NaCl) but can also be added in other forms including sodium nitrite, sodium bicarbonate (baking soda), sodium benzoate, and monosodium glutamate (MSG). These compounds are added to foods to enhance flavor, act as a binder, and/or to inhibit microbial growth to extend the shelf life of a product.
Hanna Instruments offers a wide variety of instrumentation for measuring sodium. Products include portable and benchtop pH/ISE meters that can use a sodium Ion-Selective Electrode (ISE) for direct measurement.
Titration systems are also available that determine the chloride portion of sodium chloride. The argentometric titration for chloride is a very common measurement when determining the sodium content in food. In this titration sodium chloride reacts with silver nitrate to form a sodium chloride precipitate. When there is no more chloride present for the silver nitrate to react with then free silver ions are present. The silver/sulfide ISE can then detect the excess silver. The amount of sodium present is inferred by the chloride titration.
Below are the most common products used for measuring sodium.
Titration systems, with precision dosing pumps, are available to use with a silver ISE or a silver billet electrode in performing an argentometric titration. Options for titrators include versions with two analog inputs and two dosing pumps. This configuration allows a linked titration in which acidity can be measured then sodium. A complete system includes an auto sampler that has additional pumps for the acid reagent to automatically be added when the salt titration is performed.
Benchtop pH/ISE meters
Benchtop pH/ISE meters include two channel options in which a pH probe can be connected to one channel and the sodium ISE to the other. The benchtop meters have the ion charge and formula weight pre-programmed for use with the sodium ISE. The benchtop meters also have incremental methods pre-programmed including the known addition, known subtraction, analyte addition and analyte subtraction methods.
Portable pH/ISE Meters
Portable pH/ISE and dedicated sodium meters allow the flexibility to perform an ISE measurement in spaces where there is limited bench space; the meter can be stored in a carrying case when not in use.
A glass ion-selective electrode develops a voltage due to the ion exchange that occurs between the solution and the sensing membrane. The selective glass membrane blown on the tip of the sensor exchanges ions with the solution being measured. The charge imbalance between the membrane surface and internal cell of the sensor produces a voltage that changes in response to the sample’s ion activity. When the ionic strength of the solution is fixed by the addition of ISA, the voltage is proportional to the concentration of free ions in solution. When the ionic strength of the sample is fixed by the addition of ISA, the voltage is proportional to the concentration of sodium ions in solution and the electrode follows the Nernst equation.
This category also includes the probes used when inferring sodium concretion from a chloride titration.
Solutions for sodium determination include ISE standards and ISA for calibration and measurement.
Digital refractometers are available to measure sodium chloride in solutions used with food. The optical instruments employ the measurement of the refractive index to determine sodium chloride concentration in aqueous solutions.
The instrument intended for the food industry uses internationally recognized references for unit conversion and temperature compensation. It can display the measurement of NaCl concentration 4 different ways: g/100 g, g/100 mL, Specific Gravity, and °Baumé.
Accessories magnetic stirrers to ensure adequate mixing when using an ISE.