Polarography
is an attractive analytical technique if it can be applied without any preliminary separations. With this in mind, it was decided to investigate further the polarographic reduction of molybdenum(VI), titanium(IV) and niobium(V) in order to develop rapid polarographic methods for the determination of these efements in niobium, tantalum and tungsten base alloys.
Recently HEADRIDUZ
AND HURBARD~
reported that molybdenum can be dctermined in certain niobium base alloys by a simple polarographic method using 0.5 M hydrofluoric acid-o.5 M sutphuric acid as base electrolyte. That method does, however, require a Teflon dropping mercury electrode and these arc not commercially available. In addition it would be advantageous to determine not only molybdenum but also titanium and niobium in such ~~i6h-temperature alloys, and this is not possible with the fluoride base electrolyte. It was proposed to dissolve the alloys in a mixture of hydrofluoric and nitric acids, add sulphuric acid, heat to fumes of sulphur trioxide, and then dilute with a solution of an organic acid to give the base electrolyte for polarography, since the organic acids form soluble complexes with niobium, tungsten, etc.
Previous polarographic investigations on niobium(V) in solutions of citric acidsas, EDTAsee, and tartar& oxalic, lactic, malic and gluconic acid@ have been reported, and the polarography of titanium (IV) in EDTA solution has been studied", However, in these papers, little information is given on interfering elements and further investigations on these organic acid supporting electrolytes are reported in this paper.
EXPERIMENTAL
A Sargent model XV polarograph was used. A Meites-type H-cell was employed with a solution compartment for ea. 40 ml of solution. This compartment was connected to a saturated calomel electrode by means of an agar-saturated potassium chloride bridge.
Reagents
Citric, lactic, hydrofluoric, nitric and sulphuric acids, sodium hydroxide, thorium nitrate and the disodium salt of EDTA were all of analytic& reagent grade. Other organic acids were of the purest grade available. AunZ. Chirn. Ada, 35 (xgGG) 85-90