Sensitive reversed-phase liquid chromatographic determination of fluoride based on its ternary systems with zirconium(IV) or hafnium(IV) and 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol

Abstract

Optimum conditions for the direct reversed-phase LC determination of fluoride based on the ternary M–F^––(5-Br-PADAP) complexes [M = Zr^IV or Hf^IV and 5-Br-PADAP = 2-(5-bromo-2-pyridylazo)- 5-diethylaminophenol] were evaluated. Chromatographic separation was performed with C₁₈ end-capped column with an eluent consisting of acetonitrile–water (85 +15 v/v) mixture of pH 4.0 ± 0.3 (flow rate 1 ml min^–1), and the eluate was monitored spectrophotometrically at λ_max = 585 nm. The calibration curves were linear over a wide range of fluoride concentrations: from 1 to 110 and 150 ng ml^–1 for the Zr^IV–F^––(5-Br-PADAP) and Hf^IV–F^––(5-Br-PADAP) systems, respectively (using a 20 µl loop). Under such conditions the detection limits were 0.8 and 0.7 ng ml^–1, respectively, and the quantification limit is 1.0 ng ml^–1 for both methods. When a 100 µl loop was used, the limits of both detection and quantification in the method based on the zirconium system were 0.2 ng ml^–1. Using the proposed method, fluoride was determined directly in tap water, saliva and an anti-cancer agent for prostatic cancer (Leuprolid).