SPECIATION OF MAIN-GROUP METAL-IONS BY ELECTROSPRAY MASS-SPECTROMETRY.1. INVESTIGATION OF AQUEOUS POLYSELENIDE SPECIES AND EFFECTS OF CATIONS AND PH

Polyselenide anion speciation in aqueous solution has been investigate d by electrospray mass spectrometry (ESMS). Two methods of control ove r this speciation are reported: countercation substitutions and pH adj ustments. The countercation has been found to affect the degree of dis proportionation or comproportionation. Solutions of sodium tetraseleni de displayed numerous Se-n(2-) arid HSen- species in neutral and basic solutions. In potassium solutions, the dominant species was Se-4(2-). H2O. Solutions of cesium pentaselenide also showed preference for high er-order polyselenides. The pH dependence has been analyzed in terms o f the percent Se-n(n = 2-5) present. Di-, tri-, tetra-, and pentaselen ide species were present over the entire pH range investigated, and tr ends in selenide species versus pH were developed. For example, at pH > 9, tetraselenide species were dominant.