An investigation of the optimum composition of poly(vinyl chloride) matrix membranes used for selective calcium-sensitive electrodes

Abstract

Studies of the composition parameters of the poly(vinyl chloride) matrix membrane selective calcium-sensitive electrode showed that phosphate sensor and phosphonate mediator are interdependent constituents. The most practical electrodes examined were obtained from membranes containing 28·8 per cent. w/w of poly(vinyl chloride)plus 71·2 per cent. w/w of dioctyl phenylphosphonate and monocalcium dihydrogen tetra(didecylphosphate) in a 10 : 1 weight ratio. Membranes containing only didecylphosphoric acid sensor gave sluggish electrodes with short linear response ranges. Monocalcium di(didecylphosphate) sensor produced better electrode characteristics than didecylphosphoric acid, but the membranes showed evidence of the presence of finely divided material. In complementary work, no practically useful electrodes were obtained with any of cellulose acetate, ethylcellulose, collodion and pyroxylin as alternative matrix materials to poly(vinyl chloride).