Study On Determination Of Trace Heavy Metals By Membrane Filtration Enrichment-Visible Diffuse Reflectance Spectrometry

In recent years, the diffuse reflectance spectroscopy coupled with enrichment technology has developed quickly to improve its sensitivity effectively. Based on the previous research work, a new filtration membrane enrichment technology combined with diffuse reflection spectroscopy was developed in this paper. It was aimed at solving the problem of low sensitivity of traditional visible spectrophotometry and it could be used for quantitative analysis of trace heavy metals successfully.In this work, the complexation agent1-(2-pyridylazo)-2-naphthol(PAN) was used to start the complexation reaction with heavy metal ions under the optimal conditions to form colored hydrophobic complexes.The complexes were filtered with membrane, and concentrated quantificationally on the surface of the membrane then measured by visible diffuse reflectance spectrometry. Linear relationship between the values of absorbance and mass concentration of cobalt was found in the range of0.2-3.0μg/L and3.0-10.0μg/L, with a detection limit(3S/k) of0.093μg/L. The proposed method was applied in the determination of trace cobalt in pond water and vitamin B12tablets samples, and the recoveries were between96.7%and105.0%, the relative standard deviations(n=3) range from1.40%to4.15%. The method developed was also applied to simultaneous detection of trace cobalt and zinc in the pond water where a surfactant of Brij-30was used.24mixture samples containing0.2-2.0μg/L Co2+and0.3-1.8μg/L Zn2+were designed and prepared for spectroscopic calibration with partial least squares (PLS). Leave-one-out cross-validation method was used for selecting the number of latent variables. It turned out that the root-mean-square errors of predictions (RMSEPs) of the independent prediction set containing six mixture samples were0.1663and0.1772μg/L, the average relative errors9.57%and9.92%for the two metals. With the developed method, Cd2+could be detected. It was found that the absorbance was linearly related to the concentration of Cd2+in the ranges from1.0to10.0μg/L, with a detection limit of0.387μg/L. The method was used to detect the trace cadmium in rice samples, the results showed that the recoveries were91.7%-98.2%and the relative standard deviations(n=3) range from4.72%to32.2%.