Note on the Polarographic Determination of Zirconium

Abstract

We have found that a useful polarographic method for the determination of zirconium can be based on the findings that m-nitrobenzoic acid is polarographically reducible (1,4) and that this compound is a highly selective precipitant for zirconium (3,5). In principle, the method consists of precipitating zirconium with m-nitrobenzoic acid, dissolving the filtered and washed precipitate in hydrochloric acid, and measuring the height of the polarographic wave corresponding to the reduction of the m-nitrobenzoic acid (to the hydroxylamine stage) in a suitable supporting electrolyte. The method is accordingly an indirect one for zirconium, and depends on the specificity of m-nitrobenzoic acid as a precipitant. We have applied the method successfully to the determination of zirconi~~m in magnesium-base alloys. PROCEDURETo a 5-gm. sample of the alloy, about 25 ml. of water is added followed by sufficient 16 M nitric acid (about 35 ml., in small portions) to cause ready dissolution, except for the relatively small residue which contains the so-called "insoluble" zirconium. The mixture is filtered through paper (Whatman No. 42) and the residue washed with 2.0 M nitric acid. The filtrate and washings are caught in a 250 ml. volumetric flask, from which, after making up to the mark with 2.0 M nitric acid, one or more 25 ml. aliquot samples are taken. T o each of these is added aqueous ammonia (1 :I) to the Congo red end point, with care being taken to avoid precipitation of zirconium. There are then added 20 ml. of 2.0 M hydrochloric acid, 10 gm. of ammonium nitrate, water to give a volume of about 100 ml., and then, a t the boiling point with stirring, about 100 ml. of a hot 1% aqueous solution of m-nitrobenzoic acid (5). The mixture is boiled gently for five minutes and then filtered hot through a Gooch crucible. The precipitate is washed with hot water and then dissolved in 25 ml. of 6.0 M hydrochloric acid by placing the crucible and acid in the original beaker and warming the mixture. The crucible, after it is washed down with water, is re~noved from the beaker and the contents of the beaker are neutralized to theCongo red end point wit11 aqueous ammonia (1:l) and washed with water into a 250 ml. volumetric flask. One or more 25 ml. aliquot samples are then pipetted into 100 ml. volumetric flasks, and, to each, 50 ml. of a 0.20 M solution of potassium chloride, 10 ml. of 0.20 M hydrochloric acid (by pipette), and 1 ml. of 0.75% gelatin solution (as a ~naxinlum suppressor) are added. The solution is made up to volume with water, a portion is decanted into the polarographic cell, bubbled with purified nitrogen for 15 min., and then polarographed.The polarographic wave for the first reduction step of nz-nitrobenzoic acid For personal use only.

Determination of the Natural Dissolved Concentration of Zirconium in Seawater by Adsorptive Stripping Voltammetry

“…related to the reduction of zirconyl ion. Afterwards it was assayed by polarography in magnesium-base alloys with m-nitrobenzoic acid as a selective precipitant for zirconium [12]. The majority of the voltammetric methods for Zr(IV) are related to determinations in ores and alloys [13][14][15][16][17].…”