Potentiometric determination of fluoride in geological and biological samples following pyrohydrolytic decomposition

Abstract

A method for the determination of fluoride in coal, coal fly ash, phosphate rock, limestone, mineral clay, fossilised materials, oyster tissue and vegetation using pyrohydrolysis for sample decomposition is proposed. A specific apparatus was constructed and the influence of vanadium pentoxide (V 2O 5) as a catalyst for the pyrohydrolysis reaction was investigated. It was verified that V 2O 5 does not influence the release of fluoride from the vegetation, oyster tissue, coal and coal fly ash matrices analysed. However, the catalyst was necessary for the phosphate rock, fossil bone, mineral clay and limestone samples. Certified and noncertified samples were analysed using an ion selective electrode (ISE) for the analyte detection. Precise (relative standard deviation—R.S.D.<7%) and accurate (recovery in accordance to certified values) results were obtained. The limit of quantification (LOQ) of the method was 5.0 μg g −1 of fluoride using 20 mg of sample and a final dilution to 10 ml. The sample frequency was five samples per hour.