Selective collection and separation characteristics of precious metal ions (Au³⁺, Ag⁺, Pt²⁺) were found by using poly(2-acetoacetoxy ethyl vinyl ether) {poly(AAEVE)} as a pH-sensitive polymer under the coexistence of L-ascorbic acid. The phase-transition phenomenon was shown at pH = 9.1 in an alkaline aqueous solution containing acetone. Sixty mg of poly(AAEVE) was solved with a mixed solution of an acetone (1.2 mL) and 1 M sodium hydroxide aqueous solution (1.2 mL). The polymer solution (2.4 mL) and 0.1–1.0 g L−1 L-ascorbic acid 1 mL were added to 4 mL of an elements solution; they were then gently shaken in order to from a homogeneous solution. One M of acid 2.6 mL was added to the solution and the collection behavior of metals was examined. A sedimented phase of the polymer was produced with less than pH = 9.1. As a result of a detailed examination for 62 kinds of elements, each extraction percentage of 93%, 93% and 99% was obtained for gold(III), silver(I) and platinum(II). In addition, the collection percentage was found to be changed in accordance with the L-ascorbic acid concentration.