A procedure is developed for the simultaneous determination of up to 0.5 mu
g/mL of carbonate ions and 1 mu g/mL of tetraborate ions on the basis of t
he additive catalytic action of these anions on the complexation reaction o
f aluminum with Xylenol Orange in weakly acid solutions. Concentrations of
CO32- and B4O72- ions simultaneously present in solution were calculated by
the Vierordt method, which involves solving an overdetermined set of equat
ions by the least-squares method.