A kind of novel organic/inorganic composites as ionophore in the membrane of calcium ion selective electrode, which were made of thioacetamide and attapulgite, had been prepared. Thioacetamide is a type of small organic molecule with functional groups including amino groups and carbon-sulfur double bonds. Attapulgite has been characterized by a high negative charge at its surface, a large specific surface area, and a large micropore volume due to the existence of intercrystalline cavities. Thioacetamide molecules can carry positive charges when their amino groups get protons from hydroxyl groups of attapulgite. So thioacetamide molecules with positive charges can be adsorbed on the negative surface of attapulgite by electrostatic interaction as well as hydrogen-bonding, to form a super-molecular host-guest structure. Considering the stagger arranged pores on the outer surface of attapulgite, we inferred that adsorbed thioacetamide molecules should be around the edge of pore mouth of the attapulgite. Experiments proved that the organic/inorganic complex structure promoted the ability of attapulgite adsorbing more calcium ions from the solution. Based on the attapulgite/thioacetamide composite as ionophore, the calcium ion selective electrodes were prepared using 7.0 wt% of ionophore, 43.0 wt% of polyvinyl chloride, and 50.0 wt% of dibutyl phthalate. The influence of the weight amount ratio of attapulgite to thioacetamide in the organic/inorganic composite on the calcium electrode performance had been investigated in our experiment. The experimental results showed that the prepared calcium electrode had a proximate Nernst response in the concentration range of 1.0×10^-1～1.0×10^-6 mol·L^-1. When the m_ATT:m_TAA was 0.315 in the ionophore, the prepared electrode showed a Nernstian slope of 15.2 mV·decade^-1 and a detection limit as 1.0×10^-6 mol·L^-1. Moreover, the usable pH range of the prepared electrode was from 6.0 to 10.0, and the electrode also exhibited a favorable stability with time. IR, UV and conductivity experiments etc. have been used to research the structure of the composite made of attapulgite and thioacetamide, and the working mechanism of the prepared electrode.

Key words: attapulgite, thioacetamide, organic-inorganic ionophore, polyvinyl chloride, calcium ion selective electrode