At times, silver is used in the disinfection of pools and spas, as well as in water filters. Small quantities of silver act as a bacteriostatic agent preventing the growth of bacteria. The presence of silver in water is also indicative of pollution, mainly from film manufacturers, film processors, and surface finishers. Silver levels are closely monitored since its presence in drinking water can cause discoloration of the skin, eyes, and mucous membranes.
Hanna Instruments offers a wide variety of instrumentation for measuring silver. Products include portable and benchtop pH/ISE meters that use a solid-state silver Ion-Selective Electrode (ISE) for direct measurement. The silver ISE can be used as an indicator following the progress of a halide titration with silver nitrate. 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 silver chloride precipitate. When there is no more chloride for the silver nitrate to react with then free silver ions are present. The silver/sulfide ISE is used to determine the stoichiometric endpoint.
In addition to potentiometric devices, Hanna offers a photometric method that uses reagents to determine the silver concentration in a sample. This method uses an adaptation of the 1-(2-pyridylazo)-2-naphthol (PAN) method to measure silver concentrations up to 1.000 mg/L (ppm). The method is pre-programmed in portable and benchtop photometers and a spectrophotometer.
Below are the most common products used for measuring silver.
Titration systems with precision dosing pumps are available to use with a silver ISE in performing an argentometric titration. Options for titrators include having two analog inputs and two dosing pumps. This configuration allows for a linked titration in which acidity can be measured then silver. A complete system includes an auto sampler that has additional pumps for the acid reagent to be automatically 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 silver ISE to the other. The benchtop meters have the ion charge and formula weight pre-programmed for use with the silver 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 allow the flexibility to perform an ISE measurement in spaces where there is limited bench space and can be stored in a carrying case when not in use. The meter can accept other ISEs and has the ion charge and weight pre-programmed for the specific parameter.
The silver/sulfide ISE uses a silver/sulfide pellet. The pellet is practically insoluble in the test solutions being measured and produces a potential change due to changes in the sample’s ion activity. When the ionic strength of the sample is fixed by the addition of ISA, the voltage is proportional to the concentration of silver ions in solution and the electrode follows the Nernst equation.
The silver ISE is available as either a combination design that is complete with a reference cell or a half-cell that is used with a reference electrode. The ISE is a convenient way to measure silver.
Solutions for silver measurement include ISE standards and ISA for calibration and measurement. Other solutions include the CAL Check standards for verifying and, if needed, the calibration of portable photometers. Each CAL Check standard is supplied with a Certificate of Analysis stating the accuracy and traceability of the standard.
Spectrophotometers are available that have silica methods in several ranges pre-programmed into the meter. The spectrophotometer offers the highest precision due to the quality of the optical system that has a wavelength accuracy of +/- 1.5 nm. The spectrophotometer allows for custom methods to be used as well.
Benchtop photometers include multiparameter versions for water quality and environmental analysis. Each photometer is customized to have the parameters used by a specific industry. All benchtop have a digital pH electrode input allowing it to be used as a traditional pH meter.
Single parameter portable photometer is available and it has the Hanna CAL Check feature that allows for performance verification and, if needed, recalibration using the CAL Check standards. The portable meters are available as a meter only or as a kit. The kit version includes a rugged carrying case and CAL Check standards.
Accessories include spare cuvettes and caps for photometers, magnetic stirrers to ensure adequate mixing when using an ISE.