Wiki Page, Community Fluoridation: Module 5 - Laboratory Analysis Part 2

Wiki Page
2017-07-06T15:13:24-06:00

Methods of analyzing fluoride

The colorimetric method is a simple method. The basic parts are

a source of radiant energy or light source,

the adsorption body, which we refer to as the sample, and

an energy detector to measure how much of the energy passes through the sample, and

Colorimetric

The colorimetric method (SPADNS[sodium-pair-a-sull-foe-fee-null-a-zoe-die-high-droxs-ee-nap-full-lean-die-sull-fon-ate]) of fluoride analysis can be used where no interference occurs or where the interferences are consistent (e.g., from iron, chloride, phosphate, sulfate, or color). The final fluoride test result can be adjusted for these interferences. State laboratory personnel, the state fluoridation specialist, and the water plant operator should reconcile the interferences and make the appropriate adjustment. The colorimetric method (SPADNS) of fluoride analysis is recommended for daily testing in school water fluoridation. If interferences are consistent (e.g., from iron, chloride, phosphate, sulfate, or color), the final fluoride test result can be adjusted for these interferences. State laboratory personnel and the state school technician should reconcile the interference and make the appropriate adjustment.

The colorimetric method compares reduction in the color of an indicator solution that is reduced by the presence of ions. There are competing ions that can introduce errors in measurement. Sometimes a more precise answer can be obtained by using a spectrophotometer instead of a colorimeter. This method can suffer from many operator errors in methodology.

Module 5-Water Testing from Enos C Inniss on Vimeo.

Ion selective electrode

Operators of surface water plants should use the ion electrode method of fluoride analysis because chemicals (e.g., alum) used in a surface water plant will cause fluctuating interferences in the colorimetric method (SPADNS) of fluoride analysis. A magnetic stirrer should be used in conjunction with the ion electrode method of fluoride analysis.

The specific ion electrode measures the activity of ions by measuring electrical potential. This is less influenced by competing ionic interference than the colorimeter and experiences fewer method errors that are operator related.

Now, it's time for a quiz! Click next at the bottom for Module 5 - Quiz 2.