Fluoride is best known for preventing tooth decay. Water authorities often add fluoride to drinking water to maintain approximately a 1.0 mg/L (ppm) concentration. Fluoride can be found naturally in groundwater, particularly if a reservoir is in close proximity to seawater. While fluoride does help prevent tooth decay, too little can be ineffective while too much can stain teeth.
Hanna Instruments offers a wide variety of instrumentation for measuring free fluoride in potable water, soft drinks, wine, emulsified food products, plating, and pickling acids. Products include benchtop and portable pH/ISE meters that can use a solid-state fluoride Ion-Selective Electrode (ISE) for direct measurement. Both benchtop and portable meters have the ion charge and molecular weight pre-programmed in order to take ion concentration measurements along with multiple units of measure. The benchtop meters have incremental methods built-in. The incremental methods include the known addition method in which a known volume of a known standard is added to known volume of sample. The meter takes two reading, before and after the addition, and then performs the calculation to determine the unknown concentration of the original sample. This method is useful for low levels of fluoride.
Hanna offers a variety of colorimetric methods to measure fluoride by an adaptation of the SPADNS method found in the Standard Methods for the Examination of Water and Wastewater, 23rd edition. Available technologies include Spectrophotmeter, benchtop and portable photometers, as well as the Checker HC.
Below are the most common products used for fluoride measurement.
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 fluoride ISE to the other. The benchtop meters have the ion charge and molecular weight pre-programmed for use with the fluoride 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 labs with limited bench space and can be stored relatively easily. Two models are available including one dedicated to the fluoride measurement while the other can accept other ISEs and has the ion charge and weight pre-programmed for the specific parameter.
The Fluoride ISE is available as a combination electrode with both indicating half-cell and reference half-cell. It is also available as an indicating half-cell that will be used with a separate reference half-cell. The reference half-cell with the skirted cone geometry is the preferred version to use. The gel-filled model is specifically for the dedicated fluoride portable meter.
The Fluoride ISE is available as a combination version with both indicating half-cell and reference half-cell. It is also available as an indicating half-cell that will be used with a separate reference half-cell. The reference half-cell with the skirted cone geometry is the preferred version to use. The gel-filled model is specifically for the dedicated fluoride portable meter.
Solutions for fluoride measurement include ISE standards and TISAB for calibration and measurement. The calibration standards are available with or without TISAB. The TISAB is available as TISAB II or as the concentrated TISAB III. A kit version is available that includes calibration standards with TISAB and a bottle of TISAB II to be used with the sample.
Other solutions include the CAL Check standards for verifying and, if needed, the calibration of our 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 the fluoride method 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 treatment, wastewater treatment, and water conditioning. 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 photometers are available in two ranges. The portable photometers have a 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 include a rugged carrying case and CAL Check standards.
Checker HC, like chemical test kits, are reagent based with a color change that correlates with concentration. The handheld colorimeters, like portable and benchtop instrumentation, use the Beer-Lambert principle to determine the color change. The change in color is not as subjective as with using the naked eye.
Reagents include both low and high ranges for the photometers and Checker HC. For the photometers, the reagents are available in 100 or 300 tests versions.
Accessories include the replacement fluoride module for the combination ISE and magnetic stirrers for mixing. Also available are spare cuvettes and caps for the photometers and Checker HC.