Reaction of Lead(II) with 2,6-Bis(1-hydroxy-2-naphthylazo) pyridine as a Spectrophotometric Determination of Phosphate and Citrate

Abstract

A novel heterocyclic bis-azo dye, 2,6-bis(1-hydroxy-2-naphthylazo)
pyridine (PBN) has been used as a chromogenic reagent for
lead(II) to give a 1 : 2 (M : L) violet-coloured complex at pH 7.0-
8.5 absorbing maximum at 590 nm in a 50% aqueous ethanol medium.
Sandell's sensitivity of the colour reaction is 0.0093 μg
cm^-2 with molar absorptivity of 2.22 x 10⁴ L mol^-1 cm^-1. Job's
method of continuous variations showed the composition to be
Pb(II)-(PBN)₂. Phosphate and citrate ions decompose the lead(II)-
(PBN)₂ complex quantitatively replacing PNB molecules from the
complex. Using this ligand exchange reaction, the lead(II)-
(PBN)₂ complex has been used to determine 0.2-2.6 ppm of
phosphate and 0.4-7.4 ppm of citrate spectrophotometrically.