A novel uranyl ion-selective PVC membrane sensor based on 5,6,7,8-tetrahydro-8-thioxopyrido[4′,3′,4,5]thieno[2,3-d]pyrimidine-4(3H)one

5,6,7,8-Tetrahydro-8-thioxopyrido[4′,3′,4,5]thieno[2,3-d]pyrimidine-4(3H)one (TTPTP) is used as a novel ionophore in plasticized poly(vinyl chloride) (PVC) matrix membrane sensor for uranyl ions. The sensor displays a rapid and linear response for uranyl ions over the concentration range 1.0×10−1 to 2.0×10−5 mol l−1 uranyl ion with a Nernstian slope of 30 mV per decade. The sensor response is stable for at least 2 months and exhibits good selectivity for uranyl ion over many inorganic cations and some anions. The TTPTP-based sensor works well in the pH range 2.0–3.5 and successfully employed for determining uranyl ions in 10% non-aqueous medium. The sensor is used for the determination of uranium as uranyl ions in mixtures. The results are compared with those obtained by X-ray fluorescence method.