A Study On The Application Of Methyl Isobutyl Ketone/Water Interface To Environmental Monitoring

In order to avoid the hazard of mercury used in dropping mercury electrode (DME) on chemist's health and inherit the advantages of ploarography with DME as working electrode in the area of on-line environmental monitoring, such as the momentarily renew of the drop-let's surface and the high reproducibility of experimental results, selecting a suitable organic solvent to substitute mercury used in DME is one of the most important problems to solve in liquid/liquid interface electroanalysis field. Therefore, based on the advantage of DME, the dropping electrolyte electrode was introduced to the in-situ environmental monitoring in which the high sensitivity and high stability can not be always obtained simultaneously. A new method with good quality/price ratio was expected to meet the need of in-situ environ-mental monitoring and analysis.Aliphatic ketones had been selected as reagents to substitute the common toxic NB/w and 1, 2-DCE/w systems studied in the previous researches. Meanwhile, By the renovation of reagents and method, a three-electrode system with hanging or dropping electrolyte was used in this work, so that the complex three-electrode system used before to decrease the high im-pedance and capacitance of organic phase was simplified.In this paper, with the relatively lower toxicity, higher dielectric constant and applicabil-ity for three-electrode system in the former research, methyl isobutyl ketone (MIBK) was chosen as the organic phase to form liquid/liquid interface with aqueous solution in this paper. Then two kinds of electrode devices, hanging and dropping electrolyte, was used to establish five systems to study the detection of copper, cadmium, lead, and the pH of water body re-spectively. These researches could extend the application of electro analysis in in-situ envi-ronmental monitoring and analysis. The main experimental results are as follows:1. A novel method was used to measure the content of copper ion in aqueous solution in- directly based on the principle that the excess amount of I^- can be oxidized by certain amount of Cu²⁺ and produce certain amount of I₂. In this method, square-wave voltammetry, which have higher sensitivity and easier to realize quantitatively detection, was used. Mean while, the I₂ produced in aqueous solution was extraced by organic solvent whose volume smaller than the aqueous solution. The detection limit for the determination of Cu²⁺ in this method was found to be 5×10^-5mol/L, and the concentration ranged up to 1×10^-2 mol/L gave a linear limiting current versus concentration response. For the same simulated wastewater, this method showed high accuracy compared with the result tested by sodium diethyldithiocar-bamate extraction spectrophotometry. The recovery rate of this method was 90¹20%. This approach could be applied to the indirect determination of the oxidative heavy metals in the industrial wastewater.2. Based on the special property that quatemary ammonium salt can response to OH-, the mechanism of OH- transferring from aqueous phase to organic phase facilitied by the syner-gistic effect of quatemary ammonium salt and ionic liquid was stuided by using ionic liquid as basic electrolyte. The feasibility of this system on determination the pH of alkaline waste-water was also studied. When the content of quatemary ammonium salt above 50g/L, the transferring of OH- at the liquid/liquid interface have been saturated and the peak current will be determined by the concentration of OH-. At the range of room temperature, the facor of temperature have little impact on peak current which can be neglected. The peak potential of OH- is 0.6V vs.SCE, and pH ranged from 6 up to 12 gave a linear limiting current versus concentration response. Tested by actual phthalocyanine blue dye wastewater, this method showed good accuracy.3. As sodium laurate can react with H⁺ and produce the lipophilic lauric acid, thus drive H⁺ transferring from aueous phase to organic phase. The mechanism of system sodium lau-rate-[Bmim]PF₆-MIBK/acidic aueous solution and its feasibility for the detection of pH in acidic waste water was studied. The results showed that both ionic liquid [Bmim]PF₆ and so- dium laurate can push H⁺ to transfer and the latter playes the main role. At this interface sys-tem, the peak current of H⁺ appeared at 0.12Vvs.SCE. The main problem of this method was that sodium laurate is difficult to dissolve into MIBK, even ultrasonic vibration can't make it homodisperse in the organic phase muchly. So this method have no practicality and need fur-ther research.4. Making use of the property that chelating agent can chelate with heavy metal selec-tively, this part chosed dithizone as chelating agent to push Pb²⁺ transferring at the liq-uid/liquid interface and the mechanism and applicated feasibility of the wa-ter/MIBK-dithizone system in the in-situ detection of Pb²⁺ was stuided. Meanwhile, the drop-ping , instead of hanging, electrolyte was used, which made this method closer to in-situ monitorring. The results showed that the complex peak of Pb²⁺ appeared at 0V(vs.Ag/AgCl) and the factors of acidity, quiet time, size of droplet have little impact for the experiment. The purpose of quantitative determination could be realized by making chelating agent overdos-age and the concentration of Pb²⁺ ranged from 5×10^-6 up to 1×10^-2 mol/L gave a linear limit-ing current versus concentration response.5. In this part, an attempt of making use the complexing agent, ammonium pyrrolidine dithiocarbamate, which can complex with Cd²⁺ in aqueous solution, to study the transferring of Cd²⁺ at the liquid/liquid interface, thereby analyse the concentration of Cd²⁺ was con-ducted. But the results showed that this system is very unstable,the organic phase appeared as suspension liquid, acidity was hard to control, the surface of silver wire in this system was easy to by oxidized, these factors have made the experiment can't get satisfied reproducibility.