For fluoride interference, which substance is listed as an interferent that should be removed by distillation?

For fluoride interference, which substance is listed as an interferent that should be removed by distillation?

• A. Iron
• B. Aluminum
• C. Calcium
• D. Magnesium

Answer: (B)

When testing fluoride, some dissolved metals can react with or sequester fluoride, skewing the measurement. Aluminum is a well-known interferent because it readily forms fluoride-containing species that tie up fluoride in the solution. Distillation is used as a cleanup step to separate or remove aluminum-containing species so that the fluoride that is measured reflects the true concentration in the sample. The other metals listed—iron, calcium, and magnesium—can interfere in other ways or be addressed by different pretreatment steps, but aluminum specifically is the one identified for removal by distillation due to its strong interaction with fluoride.

When testing fluoride, some dissolved metals can react with or sequester fluoride, skewing the measurement. Aluminum is a well-known interferent because it readily forms fluoride-containing species that tie up fluoride in the solution. Distillation is used as a cleanup step to separate or remove aluminum-containing species so that the fluoride that is measured reflects the true concentration in the sample. The other metals listed—iron, calcium, and magnesium—can interfere in other ways or be addressed by different pretreatment steps, but aluminum specifically is the one identified for removal by distillation due to its strong interaction with fluoride.