| Metal pollution is mainly caused by heavy metals and their toxic substances, which result in environmental pollution. But as mining, sewerage irrigation, exhaust emission, smelting, processing and commercial manufacturing activities increased, lots of heavy metals such as lead, cadmium, mercury, etc. are discharged into the environment. This pollution gets across food chains into biogeocenose and enriches in the body or biogeocenose. When their concentration exceeds a certain limit, they will result in strong toxicity to the organism. At present, the importance of controlling the level of environmental pollutants has generated increasing interest in the development of new methods for the detection of metals ions. Recently, the available methods are used to determine metals ions such as atomic absorption spectrometry, flame photometry, inductively coupled plasma atomic emission spectrometry, isotope dilutionmass spectrometry, neutron activation analysis, inductively coupled plasma mass spectrometry, X-ray fluorescence spectrometry, etc. However, these methods are time consuming, not suitable for large scale monitoring, involving multiple sample pretreatment and relatively expensive. Thus, it is necessary to develop a sensitive, economical and convenient method to determine metals ions. Ion-selective electrodes (ISEs) that offer many advantages, such as easy handling, non-destructive analysis, good accuracy, fast response time, good selectivity, high sensitivity, simplicity and low cost, etc., have been proposed as a convenient method for environmental analysis and ionic species determination. In the past few decades, a lot of ion selective electrodes based on different ionophores have been reported. Nowdays, using new materials in the ion selective electrode is a very active direction on the studies of the ion selective electrodes. In this paper, we emphatically focus on the design, synthesis of novel complexes and new materials which are used as ionophores of PVC membrane electrode and carbon paste electrode. At the same time, the proposed electrodes are applied to the detection of metal ions in real samples. 1. Studies on the 1-benzothiazol-3-benzoyl-thiocarbamide application on Sr (Ⅱ) ion selective electrodeA new selective strontium (Ⅱ) PVC membrane electrode based on the 1-benzothiazol-3-benzoyl-thiocarbamide (BTBTA) ligand as neutral ionophore has been developed. Its performance is compared with recently reported electrodes in many respects and shows significant superiority over them, such as linear concentration range (4.0×10-7 to 1.0×10-1mol/L), sensitivity (with a detection limit of 2.5×10-7 mol/L), good selectivity, stability and reproducibility. The response mechanism was discussed in view of the AC impedance and UV-visible spectroscopic techniques. It was used as an indicator electrode in potentiometric titration of strontium ion against EDTA. At the same time, the electrode was successfully applied to the determination of strontium ions in soil and tea.2. Studies on a new macrocyclic Schiff base ligand application on La (Ⅲ) ion selective electrodeA polymeric membrane selective electrode based on a neutral ionophore N, N'-bis-(3-carboxyl-salicylidene)-thiocarbohydrazide (H2L) Schiff base ligand for detection of lanthanum (Ⅲ) ion was proposed. The response performances of the electrode has significantly improved, such as linear range, detection limit, response time. In order to obtain a clue about the stability and selectivity of the resulting complexes, in preliminary experiments, the complexation of H2L with some cations was investigated conductometrically in a DMSO solution. The results showed that the change in conductance of La3+ was larger than that for other cations. Then, the response mechanism was discussed in view of the AC impedance technique. The electrode was successfully applied in the potentiometric titration of La3+ ions with EDTA and in determination of F- ions in mouth wash, toothpaste and sodium fluoride tablets preparations.3. Studies on Derivatized Multi-walled Carbon Nanotubes application on lead (Ⅱ) carbon paste electrodeFor the first time a novel derivatized multi-walled carbon nanotubes-based Pb2+ carbon paste electrode is reported. The introduce of carbon nanotubes in the electrode, have largely improved the performance of the lead sensor, such as Nernstian linear range from 5.9×10-10 to 1.0×10-2 mol/L, a detection limit of 3.2×10-10 mol/L, a wide pH range (2.5-6.5), a fast response time (25 s) at 25℃. Moreover, it also shows a high selectivity and a long life time (more than 3 months). The selectivity coefficients of Pb2+ carbon paste electrode were determined by the separate solution method (SSM). The electrode is selective towards Pb2+ ion over a number of other cations except for Cd2+ ion, as the selectivity coefficient value is slightly higher. To know the exact concentration of Cd2+ ion that can be tolerated in the determination of Pb2+ ion, some mixed run studies were carried out, and the proposed electrode could tolerate Cd2+ ion at the concentration≤1.0×10-4 mol/L. Importantly, the response mechanism of the proposed electrode was investigated by using AC impedance technique. Finally, the electrode was successfully applied for the determination of Pb2+ ion concentration in environmental samples, e.g. soils, waste waters, lead accumulator waste and black tea, and for potentiometric titration of sulfate anion. |
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