New Type of Flotation of Ion-association Compounds of Complexes of Multicharged Anions with Basic Dyes

Sparingly soluble Ion—association compounds Thrmed between multicharged anionic complexes ( formed from trace amounts of an element to be preconoentrated and determined) and hydrophobic basic dyes, accumulate at the phase boundary after shaking with a solvent of low polarity, This type of flotation (without surfactant and gas bubbling) depends on the acidity, the dyestuff and the flotation agent. The separated compound can be deter— mined with use of any suitable method, Combination of this separation technique with spectrophotometry allows a very sensitive determination, because 2—5 dye cations correspond to one atom of the element in the multicharged anion. Examples of separation and determination of the six pla— tinum metals (i—io pg) prove the effectiveness and preci-' sion of the proposed technique. Multicharged anionic complexes, containing an analyte element, form spa— ringly soluble ion—association compounds with singly—charged cations of some basic dyes. These products are not extracted by nonpolar organic solvents but after shaking an aqueous solution with these solvents, the compounds accumulate at the phase boundary or adhere to the wall of the separatory funnel. After careful removal of both liquid phases and washing, the precipitate adhering to the wall of the separatory funnel can be dissolved in a small volume of a polar solvent (acetone, methanol, etc). In the solution obtained the isolated trace element can be determined by any suitable method. However because of the intense colour of the basic dyes it is of great advantage to combine the flotation separation with spec tropho tome try. The use of a term flotation for the technique described (ref. i) is justified, because flotation consiSts of collecting solid particles, present in suspension, on the surface of gas bubbles or on organic solvent droplets in an aqueous phase. Accumulation and concentration of particles at the phase boundary is a common feature of flotation processes. The flotation of the present ion—association compounds takes place without addition of a surfactant, because they contain basic dyes with several aromatic rings, and thus form hydrophobic particles. The shaking of an aqueous suspension of the sparingly soluble ion—association compounds with a weakly polar organic solvent replaces the gas bubbling used in analytical precipitate or ion flotation with the participation of surfactants (refs. 2, 3). The present type of flotation can therefore be considered as a modification of precipitate flotation. Numerous elements form mu]ticharged anionic complexes able to associate with basic dyes. These include the anions of the heteropolyacids of silicon, germanium, phospborus(V) and arsenic(V), the bromide complexes of bismuth and tellurium(IV), the thiocyanate complexes of molybdenum and tungsten, and the iodide complexes of cadmium With suitable basic dyes all these anionic complexes form ion—association compounds which are the basis of very sensitive fiotation—spectrophotometric methods for determination of these elements (ref. 4). FLOTATION OF PLATINUM METALS IN TRACE AMOUNTS SuitaleanLonic. complexes and asip, dyes n hydrochloric acid (see Table i), in the presence of tin(II), platinum metals form multicharged anionic complexes with platinum—tin bonds (ref.5). For platinum, rhodium and iridium, their complexes with 5nCL,, and presumably also with chloride, have been found to be the most sUitable for the formation of ion—association compounds with basic dyes for flotation purpose refs. 6—il). Bromide and thiocyanate complexes have proved to be