Determination Of Trace Amounts Of Bismuth Using Cloud Point Extraction And Determination By Hydride Generation Atomic Fluorescence Spectrometry

ObjectiveBismuth is a kind of rare metal in the form of free metals and minerals in nature. With their particular characteristics, bismuth compounds are also widely used in medicine, cosmetic preparations, alloys, semi-conductors, metallurgical additives and chemical pigment. With the increased use of bismuth, the waste discharge of bismuth has increased in the related industries simultaneously, which may reflect on the level of bismuth in natural water. As reported, the plants which have been watered using the water containing high concentration of bismuth may be caused perish even to death. As the exploitation and utilization of bismuth increases, the chance of human exposure to it has greatly increased. Therefore, it is important to develop a high selective and sensitive, environmental benign, economical technique for the determination of bismuth at trace levels in water, serum and urine samples. That plays an important role in the assessment of occupational and environmental exposure, healthy protection and clinical diagnosis. Since bismuth concentration in biological and environmental samples is very low, it is necessary to take the process of separation and preconcentration of ultra-trace amounts of bismuth before determination. In addition, the process of extraction can separate this element from matrix and reduce the interference, so the sensitivity and selectivity of determination can be greatly improved simultaneously.Cloud point extraction (CPE) is one kind of current enrichment technique, which is based on the clouding phenomenon of the micellar aqueous solution of surfactants over a certain temperature, concentrates and extracts the metal complex into the hydrophobic surfactant-rich phase by changing the experimental parameters. This preconcentration technique only uses a very little amount of nonionic or zwitterionic surfactants detergents in lieu of a large amount of toxic organic solvents. Thus, the cloud point extraction offers several advantages over conventional liquid-liquid extraction techniques in terms of lower cost, good concentration efficiency, environmentally lower toxicity and safety. This technique has been widely used for separation and analysis of biomacromolecule, traces metal elements and organic toxicants.This study aims at the determination of bismuth in drinking water, serum and urine samples by hydride generation atomic fluorescence spectrometry after cloud point extraction. A few drops of antifoam have to be added in order to restrain foam before the process of instrumental determination, which plays an important role in the implementation of this method. That will provide an environmental benign, high efficient, easy and green analytical method for determination of bismuth.MethodsThis study is based on the micelle-mediated extraction of the complex of Bi3+with dithizone and a kind of nonionic surfactant Triton X-114 as the extraction agent. After that, bismuth in the surfactant-rich phase was determined by hydride generation-atomic fluorescence spectrometry. The optimized conditions of lamp current, negative high-voltage and the carrier gas flow rate were chosen by means of orthogonal experimental design. During the process of cloud point extraction, the main factors affecting CPE efficiency, such as pH of sample solution, concentration of dithizone and Triton X-114, the dosage of antifoam, the time of ice-water bath, were optimized in detail. The proposed method is applied to determination of trace amount of bismuth in drinking water, serum and urine samples.Results1. As the experimental results shown, the optimized conditions were 30/30 mA of the lamp current(P/A),280 V of negative high-voltage,800 mL/min of the carrier gas flow rate,10.0 g/L of potassium borohydride solution,2.4×10-5mol/L of dithizone concentration, pH 5.6, Triton X-114 (0.32%, w/v), the equilibrium temperature of 55℃, cooling in ice-water bath for 30 min.2. Under optimum conditions, linearity was obeyed in the range of 0.025-2.0μg/L of bismuth and regression equation of working curve was If=21.51c-0.88 (r=0.9997). The coefficient of variation in this method was less than 7% (n=6) and the detection limit of the method was 0.015μg/L.3. Under optimum conditions and 0.015μg/L of the detection limit in the proposed method, it was applied to the determination of bismuth in drinking water samples with satisfactory results and the average recoveries between 94.0% and 94.8% were obtained.4. Under optimum conditions and 0.015μg/L of the detection limit in the proposed method, it was applied to the determination of bismuth in urine and serum samples with satisfactory results and the average recoveries between 89.4% and 89.9% in urine samples, between 92.0% and 97.5% in serum samples were obtained respectively.ConclusionWith dithizone as the complexing agent and a nonionic surfactant Triton X-114 as the extraction agent, this developed method has been used to measure the ultra-trace amount of bismuth in serum samples successfully. The use of antifoam makes the HG-AFS coupled with CPE possible for this element, which has not yet been reported. The method was high sensitivity and selectivity, low detection limit, but also did not use toxic and harmful organic solvents, which is harmless to the health of analysis and environmental protection. The innovative technique was applied to the determination of bismuth in drinking water, serum and urine samples with satisfactory results.