Enrichment And Determination Of The Ultra-trace Heavy Metals In Enviromental Water

The character of water samples with complication and extremely low level of pollutants needed treat before the analysis. Liquid-liquid extraction as a simple, mature technology of sample preparation methods for separation and enrichmen of the water samples with low content of heavy metals. By selecting a suitable extraction reagent and extraction solvent can improve the results of the enrichment. A highly selective, sensitive and water-solution reagent o-Carboxybenzenediazoaminoazobenzene (o-CDAA) synthesized coupled with neural network for dertemination of the cadmium(II) and nickel(II) simultaneously in the water. Temperature-collected ionic liquid replaced the traditional organic solvents with o-CDAA was used to extract the cadmium(II), mercury(II) and nickel(II) in the water.In the presence of borax buffer solution (pH10.2), cadmium (II) and nickel (II) reacts with o-CDAA to form red complex with maximum absorption at 525 and 540nm, respectively. Based on the difference in absorption spectrometry of the two above complex, sixteen calibration samples which were composed by cadmium and nickel were prepared to train the network. By choosing wavelengths, number of nerve cell in the hidden layers and the training function, the parameters of the network were optimized and the spectrophotometry coupled with BP neural network was developed for determination of trace cadmium and nickel. The method has been applied to determine the trace of cadmium and nickel in the waste water from battery factory. The recovery of Cd²⁺, Ni²⁺ was 93% and 106%, this indicates the method has good accuracy.Applied on temperature-controlled ionic liquid 1-isooctyl-3-methylimidazolium hexafluorophosphate ([i-C₈mim][PF₆]) as extraction solvent, o-CDAA as extraction reagents and nitric acid as back-extraction solvent, cadmium(II), nickel(II) and mercury(II) in the water were researched to extract and back-extract. By examining the extraction temperature, mixing time, ionic liquid dosage, the amount of nitric acid and other factors, the optimal experimental conditions were determined. In this condition, the enrichment factor was 500 times. Based on the extraction-system, cadmium(II), meucruy(II) and nickel(II) were determinated by ICP-OES. The results showed that one step extractions were all above 95% and the determination limits were 5ng/L, 50ng/L and 20ng/L. It was successfully applied to determinate the metals in the environmental water with satisfactory results.The ratio of cadmiud with o-CDAA was measured and determinated the composition of the complex with negatively charged by molar ratio method. Chloroform, 1-butyl-3- methylimidazolium trifluoromethyl sulfonamide salt and 1-butyl-3-methyl- imidazolium hexafluorophosphate were used to extract the complexes. The results indicated that the extraction process may exit anion exchange reaction. In addition, the visible absorption experiments further showed that the ionic liquid extraction process exit the anion exchange. Therefore, cadmium(II) in imidazolium hexafluorophosphate extraction system performanced anion exchange mechanism.