PA.FPNS: its synthesis and use in spectrophotometric determination of magnesium.

A new polymeric chromogenic reagent PA.FPNS has been synthesized by condensing polyallylamine (PA) with 3-(4-formylphenylazo)-4,5-dihydroxynaphthalene-2,7-disulfonic acid (FPNS) and its properties studied. In alkaline media, PA.FPNS reacts with magnesium to form a water-soluble blue complex, whose absorption maximum is at 604 nm. The molar absorptivity (varepsilon) of the complex is 5.2 x 10(4)l mol(-1) cm(-1), which is four times that of the FPNS-Mg complex, and Beer's law is obeyed over the range 0-0.35 mug ml(-1) magnesium. Compared to the corresponding low-molecular-weight FPNS and other chromogenic reagents, PA.FPNS offers considerably improved sensitivity and selectivity for magnesium, which may be attributed to incorporating FPNS into a water-soluble polymer and the effect of the polymeric chain on the reaction microenvironment. Also, a simple and sensitive spectrophotometric method for the determination of magnesium has been developed and applied to water and human fluid samples with satisfactory results.