What are the two approved methods for the detection of fluoride in samples?

The two approved methods for the detection of fluoride in samples are indeed Ion-Selective Electrode and SPADNS. The Ion-Selective Electrode method is particularly effective because it allows for direct measurement of fluoride ions in a variety of water samples and offers high sensitivity and specificity. It functions by using a membrane that selectively permits fluoride ions to pass through, generating a potential that can be correlated to fluoride concentration.

The SPADNS method, on the other hand, is a colorimetric technique that involves the formation of a colored complex when fluoride ions react with a specific reagent. This complex is then measured using a spectrophotometer, allowing for quantification of fluoride levels based on the intensity of the color.

Both methods are widely recognized for their reliability and accuracy in analyzing fluoride concentrations and are utilized in compliance with water testing regulations to ensure safe drinking water standards. Other methods mentioned in the other choices are not typically used for the specific detection of fluoride in water samples.