The measurement of sodium is very common in the food industry. With potentiometric sensors this is ether done directly with a sensor that measures sodium or indirectly by a sensor that can detect the excess of silver from a silver nitrate titration of chloride. The silver nitrate reacts with sodium chloride to form a silver chloride precipitate. When all of the chloride is precipitated then there will be an excess of silver ions that will be detected by the sensor (see figure below). Since the sensor is detecting chloride the titration is an indirect method of measuring sodium and assumes all chloride is from sodium and all sodium is in the form of sodium chloride.
Other halide titrations include chloride in brine solutions, wastewater, fertilizer and concrete due to the corrosive effect on iron rebar that is used for support.
There are two types of sensors available for performing the chloride titration with silver nitrate. They include the solid-state sensors, such as silver or chloride ion selective electrodes (ISEs), or a metal electrode such as the silver billet electrode. ISEs are expensive and can be problematic if left in solution for a long time due to the softening of the compressed sensing pellet. The silver billet is economical and does not soften with extended periods of time in solutions making it ideal for high throughput sampling.
The HI5148B uses a platinum pin, glass body, open junction with CPS technology and is refillable with 3.5M KCl or another electorlyte based on user requirments.
The HI5148 sensor is made with a silver rod known a a billet
CPS™ Sleeve Junction
Clogging Prevention System (CPS™) technology is an innovation in electrode technology. Conventional electrodes use ceramic junctions that clog quickly with precipitates from a halide titration. When the junction is clogged, the electrode does not function. CPS technology utilizes the porousness of ground glass coupled with a PTFE sleeve to prevent clogging of the junction. The ground glass allows proper flow of the liquid, while the PTFE sleeve repels dirt. As a result, electrodes with CPS stay fresh up to 20 times longer than conventional electrodes.
The glass body is ideal for laboratory use. The glass is resistant to many harsh chemicals and is easily cleaned. The glass body also allows for a fast transfer of heat to the internal reference electrolyte. The mV generated by the reference cell is temperature dependent. The faster the electrode reaches equilibrium, the steadier the reference potential.
Double Junction Reference
A double junction electrode has an internal compartment surrounding the reference wire. Silver ions are present in the electrolyte of the internal compartment, which houses the Ag/AgCl reference wire; the electrolyte outside this compartment is silver free. The double junction design allows for various eleclroytes to be used incluing KCl and potassium nitrate.
The HI5148B is a refillable probe. The fill cap should be removed prior to measurement. Removing the cap creates positive head pressure in the reference cell allowing for higher flow rate of electrolyte through the outer junction. A higher flow rate will result in a faster and more stable reading.
The HI5148B uses a BNC connector. This type of connector is universal in that it can be used on any titration system that has the female BNC probe input. Other type of connectors include DIN, screw type, T-type, and 3.5mm to name a few. These types of connectors tend to be proprietary for a particular type of meter and are not interchangeable.