Lanthanum ions accelerate hydrolysis of phosphate ester binding by 13 orders of magnitude. This suggests that the phosphate diester in DNA may also suffer such destruction. Thus, lanthanum should be situated among the class of highly toxic metal ions that are potentially effective against micro-and higher-organisms. Lanthanum chloride manifests anti-tumor activity. Genotoxicity of lanthanum(III) in human peripheral blood lymphocytes has also been reported. Lanthanum chloride caused changes in

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... pid peroxidation, the redox system, and ATPase activities in plasma membranes of rice seeding roots. 1-3 Lanthanum oxide is widely used in the preparation of optical glasses, glass fibers for optical purposes, gasoline-cracking catalysts, polishing compounds and carbon arcs, and in the iron and steel industries to remove sulfur, carbon, and other electronegative elements from iron and steel. 4 Thus, because of the increasing interest in the bioinorganic and coordination chemistry and the increased industrial application of lanthanum compounds, determination of the lanthanum ions is very necessary. The main available methods for low-level monitoring of rareearth ions in solution are spectrophotometry, inductively coupled plasma mass spectrometry, and inductively coupled plasma atomic emission spectroscopy. Isotope dilution mass spectrometry, neutron activation analysis, and X-ray fluorescence spectrometry, etc., are also used in some laboratories. These methods are either low in sensitivity, or time-consuming, or involve multiple sample manipulations, or are too expensive for most analytical laboratories. Potentiometric detection based on ion-selective sensors, as a simple method, offers great advantages such as speed and ease of preparation and procedures, relatively short response times, reasonable selectivity, wide linear dynamic range, and low cost. These characteristics have inevitably led to electrodes for several ionic species, and the list of available sensors has grown substantially over the past few years. 5 Due to the critical importance of selective La(III) ion determination, especially in biological, industrial and water samples, there are a number of recent reports on the preparation of La(III) selective membrane electrodes based on a variety of ionophores. [6] [7] [8] [9] [10] [11] [12] [13] [14] Recently, we have reported a number of electrodes for anions and metal ions. [15] [16] [17] [18] [19] [20] [21] In this paper, we report a highly selective and sensitive solvent polymeric membrane electrode (PME) for La(III) ion based on the NPYFH (Fig. 1) . Experimental Reagents Reagent grade dibutyl phthalate (DBP), benzyl acetate (BA), acetophenon (AP), nitrobenzene (NB), sodium tetraphenyl borate (NaTPB), tetrahydrofuran (THF) and high relative molecular weight PVC were purchased from Merck and 943 A highly La(III) ion-selective PVC membrane sensor based on N′-(1-pyridin-2-ylmethylene)-2-furohydrazide (NPYFH) as an excellent sensing material was successfully developed. The electrode shows a good selectivity for La(III) ion with respect to most common cations including alkali, alkaline earth, transition and heavy metal ions. The proposed sensor exhibits a wide linear response with slope of 19.2 ± 0.6 mV per decade over the concentration range of 1.0 × 10 -6 -1.0 × 10 -1 M, and a detection limit of 7.0 × 10 -7 M of La(III) ions. The sensor response is independent of pH in the range of 3.5 -10.0. The proposed electrode was applied as an indicator electrode in potentiometric titration of La(III) ion with EDTA.