Novel Cesium Membrane Sensor Based on a Cavitand Mohammad Reza Ganjali, a * Parviz Norouzi, a Mehdi Emami, a Mahmoud Golmohammadi a and Arash Mouradzadegun b a Department of Chemistry, Tehran University, Tehran, Iran b Department of Chemistry, Shahid Chamran University, Ahvaz, Iran A PVC-based membrane sensor was prepared for Cs + ions, which was based on 7,11,15,28-tetraiodo- 1,21,23,25-tetramethyl-2,20:3,19-dimethano-1H,21H,23H,25H-bis[1,3]dioxocino[5,4-i:5 ¢ ,4 ¢ i ¢ ] benzo[1,2-d:5,4-d¢]-bis[1,3]benzodioxocin stereoisomer (cavitand). The proposed membrane electrode exhibits a linear dynamic range of 1.0 ´ 10 -1 -1.0 × 10 -5 M, with a Nernstian slope of 59.1 ± 0.3 mV per decade, and a detection limit of 5.0 ´ 10 -6 M. It has a very fast response time of <10 s and can be used for at least eight weeks without any considerable divergence in its potentials. The best sensor performance was obtained with a membrane containing 30% PVC, 62% dibutylphthalate (DBP), 6% cavitand, and 2% potassium tetrakis(p-chlorophenyl) borate (KTpClPB). The sensor could be used in a pH range of 4.3-9.5. Keywords: Cesium; Potentiometry; Cavitand; PVC membrane; Sensor. INTRODUCTION Cesium and the other alkali metal ions can be deter- mined by conventional spectroscopic methods such as atomic spectrometry and inductively coupled plasma mass spectrometry. 1 Potentiometry, using ISEs, is now widely used for simple and rapid measurements of alkali metal ions, particularly in clinical and environmental assays. Polymeric carrier-based ion-selective electrodes (ISEs), which are selective towards the alkali and alkaline earth metal ions such as sodium, potassium and lithium, have been the focus of numerous studies. 2 Some of these studies have been on the development of cesium ion-selective membrane sensors based on different ionophores, espe- cially calix[4]arenas and crown ethers such as 1,3-alternate thiacalix[4]biscrown-6,6, calix[4]crown ether–ester, and biscalix[4]arenes. 3-11 However most of these sensors suffer from low selectivities and relatively high detection limits. Recently, our group has reported a number of selec- tive and sensitive membrane sensors for some alkali and al- kaline earth, and some transition and heavy metal ions. 12-18 In this report we wish to introduce a highly selective mem- brane sensor based on a new cavitand that can be used for the fast monitoring of cesium ions. EXPERIMENTAL SECTION Reagents and Materials Reagent grade benzyl acetate (BA), dibuthyl phth- alate (DBP), ortho-nitrophenyloctyl ether (NPOE), potas- sium tetrakis(p-chlorophenyl)borate (KTpClPB), oleic acid (OA), tetrahydrofuran (THF), and high relative molec- ular weight PVC (all from Merck) were used as received. The nitrate and chloride salts of all cations used (all from Merck), were of the highest purity available and were used without any further purification except for a vacuum drying over P 2 O 5 . Doubly distilled de-ionized water was used throughout the experiments. Synthesis of Cavitand To synthesize 7,11,15,28-tetraiodo-1,21,23,25-tetra- methyl-2,20:3,19-dimethano-1H,21H,23H,25H-bis- [1,3]dioxocino[5,4-i:5¢,4¢i¢]benzo[1,2-d:5,4-d¢]-bis[1,3]- benzodioxocin stereoisomer (cavitand Fig. 1), 2,8,14,20- tetramethylpentacyclo [19.3.1.1 3.7 .1 9.13 .1 15.19 ]octacosa-1- (25),3,5,7(28),9,11,13(27),15,17,19(26),21,23-dode- caen-4,6,10,12,16,18,22,24-octol stereoisomer (A) should be lithiated. Before lithiating A, it was important to drive off reactive solvents (such as CH 2 Cl 2 ) entrapped in its crys- Journal of the Chinese Chemical Society, 2006, 53, 1209-1214 1209 * Corresponding author. Fax: +98 21 6495291; E-mail: Ganjali@khayam.ut.ac.ir