AQUEOUS COMPLEXING OF NICKEL AND ZINC WITH 3-(N-MORPHOLINO)PROPANESULFONIC ACID AND THE SOLUBILITY PRODUCES OF NICKEL AND ZINC HYDROXIDES

Phosphate and carbonate buffers serve as excellent pH buffers at circu mneutral values of pH, except for systems requiring significant concen trations of heavy metals, which are severely restricted by the low sol ubilities of heavy metal phosphates and carbo nates. 3-(N-morpholino)p ropanesulfonic acid (MOPS; pK(a) 7.2) is a suitable replacement buffer at circumneutral values of pH. However, only limited data are availab le concerning aqueous complexing involving MOPS. Aqueous complexing of nickel and zinc with MOPS has been investigated by the solubility met hod, using the sparingly soluble solids Ni(OH)(2) and Zn(OH)(2). Log K -sp values of -15.9 and -16.6 have been determined for NI(OH), and Zn( OH), respectively. Experiments with MOPS indicate that there is neglig ible complexing between Zn and MOPS, but that significant Ni-MOPS comp lexing occurs, such that Ni2+ +OH- +MOPS(-) reversible arrow Ni(OH)MOP S degrees; log K = +7.0.