1RYHO7KDOOLXP,6HOHFWLYH0HPEUDQH(OHFWURGH%DVHGRQD3RGDO/LJDQG %XOO.RUHDQ&KHP6RF9RO1R Novel Thallium(I)-Selective Membrane Electrode Based on a Podal Ligand Mohammad Reza Ganjali, * Mohammad Reza Pourjavid, Arash Mouradzadegun, † Morteza Hosseini, and Farhang Mizani Department of Chemistry, Tehran University, Tehran, Iran † Department of Chemistry, Shahid Chamran University, Ahvaz, Iran Received March 6, 2003 A PVC-based membrane electrode for thallium(I) ions based on 1,21,23,25-tetramethyl-2,20: 3,19-dimetheno- [H, 2] H, 23H, 25H-bis-[1,3] dioxocino[5,4-i:5',4'-i] benzo [1,2-d: 5.4-d'] bis [1,3] benzodioxocin(II) has been prepared. The electrode displays a linear dynamic range of 1.0 × 10 -1 -1.0 × 10 -5 M, with a Nernstian slope of 59.8 ± 0.2 mV decad -1 , and a detection limit 5.0 × 10 -6 M. It has a very fast response time of <10 s and can be used for at least ten weeks without a considerable divergence in potentials. This electrode revealed comparatively good selectivity with respect to alkali, alkaline earth, and some transition and heavy metal ions and was effective in a pH range of 2.0-10.0. It was used as an indicator electrode in potentiometric titration of thallium ion with sulfide ion. Key Words : Podal ligand, Thallium(I) selective membrane, Potentiometry, PVC Introduction Thallium is toxic, especially as its monovalent cation. From the environmental and biological viewpoints, soluble univalent thallium compounds, e.g., thallium(I) sulfate, acetate and carbonate are very toxic because they are easily absorbed into the human body by skin contact or ingestion. 1 Thallium poisoning in the human body has to be checked quickly by analyzing urine and blood samples. Atomic absorption spectroscopy and polarography have already been recommended for the thallium(I) assay. A more compact instrumentation for the thallium(I) assay in human body fluids is the thallium(I)-selective membrane electrode. Ion-selective electrodes based on ionophores are well established for many inorganic cations and anions. During the last two decades, a large number of ionophores, especially a wide variety of neutral macrocyclic polyethers, has been developed and found widespread applications in potentiometric and optical sensors for the determination of respective ions in real samples. 2 The design and function of synthetic ionophores for ion-selective electrodes are based on such diverse parameters as the structure and cavity size of the ligand, the stability and selectivity of its metal ion complex, its solubility and the ability to extract the metal ion into membrane phase. Crown ether and calix[4]aren derivatives have been tested as thallium(I)-neutral carriers for ion-selective electrodes, 3-12 and the resulting thallium(I)-selective electrodes gave good results. However, since crown ethers and calix[4]arens generally have a high affinity for alkali-metal ions and in some cases silver, these thallium(I) electrodes suffer from severe interference by Na + , K + , Cs + and Ag + . In the present study, we wish to introduce a novel thallium(I) electrode by incorporation of a podal ligand as a suitable neutral ionophore for fast monitoring of thallium ion. Experimental Section Reagents. Reagent grade benzyl acetate (BA), dibuthyl phthalate (DBP), dioctyl phthalate (DOP), potassium tetrakis (p-chlorophenyl)borate (KTpClPB), sodium tetraphenyl borate (NaTPB), tetrahydrofuran (THF), and high relative molecular 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 vacuum drying over P 2 O 5 . Doubly distilled de-ionized water was used throughout the experiment. Synthesis of podal ligand. The podal ligand was synthe- sized in two steps as follow; Step 1. Synthesis of 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-dodecaen 4, 6, 10, 12, 16, 18, 22, 24-octol (I). Resorcinol (342 g, 3.11 mol) was dissolved in 620 mL of ethanol and 310 mL of 37% aqueous HCl. To this stirred solution was added slowly 137.1 g of CH 3 CHO. Immediately after the addition was complete, the reaction was cooled in a water bath to control the exotherm. The reaction mixture was then maintained at 80 ºC for 16 h, and the yellow needles that separated were collected and washed with cold 1 : 1 ethanol-water until the washing was light yellow to give material dried at 80 o C at 10 -1 Torr for 30 h (310 g, 73%). The physical properties of this compound corresponded to those reported, and the material was suitable for use in subsequent reactions. $905 6\QWKVLV RI WHWUDPHWK\O GLPHWKHQR++++ELV>@GLR[RFLQR>L L@EHQ]R>GG@ELV>@EHQ]RGLR[RFLQ,,7RD PL[WXUHVWLUUHGDW R &XQGHU$URI/RIGU\'062 DQG J PRO RI ILQHO\ JURXQG GU\ . &2 ZHUH * Corresponding author. Fax: +98-21-640-5141; e-mail: ganjali @khayam.ut.ac.ir