Aqueous complexing of nickel and zinc with 3-(N-morpholino)propanesulfonic acid and the solubility products of nickel and zinc hydroxides.
Phosphate and carbonate buffers serve as excellent pH buffers at circumneutral values of pH, except for systems requiring significant concentrations of heavy metals, which are severely restricted by the low solubilities of heavy metal phosphates and carbonates. 3-(N-morpholino)propanesulfonic acid (MOPS; pK(a) 7.2) is a suitable replacement buffer at circumneutral values of pH. However, only limited data are available concerning aqueous complexing involving MOPS. Aqueous complexing of nickel and zinc with MOPS has been investigated by the solubility method, 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)(2) and Zn(OH)(2) respectively. Experiments with MOPS indicate that there is negligible complexing between Zn and MOPS, but that significant Ni-MOPS complexing occurs, such that Ni(2+) + OH(-) + MOPSNi(OH)MOPS composite function: log K = +7.0.
Poulson
S R
SR
Drever
J I
JI