Simultaneous Visual Detection Of Ultra Trace Heavy Metal Ions-Lead And Cadmium

Heavy metal pollution is becoming worse and worse in recent years, so it is necessaryto develop a low cost, high sensitivity and easy processing technology to detect heavymetal ions. It is of great significance for the protection of environment, life and health ofanimals and plants. There are some now available methods to detect trace amounts ofheavy metals, for example, atomic spectroscopy, mass spectrometry, electrochemicalmethod and so on. However, these methods have some problems such as time-consuming,high testing costs, depending on large-scale equipment or instruments and requiringprofessional testing personnel. In a word, they are not suitable for on-site、 rapiddetection.Test strip has unparalleled advantages on detection of heavy metal ions, which isexpected to make a breakthrough on trace analysis of heavy metal ions. However, thereare still many unresolved problems on the existing test strips. Some strips have lowersensitivity than the national standard requiring; and some strips with high sensitivity needharsh reaction conditions and complicated steps, and make it difficult for promotion andpopularization. Therefore, building a simple, rapid, highly sensitive test strip is the mainway to promote the heavy metal analysis.As an ancient detection of heavy metal ions, colorimetric detection has someadvantages including simplicity, visualization of coloration, and is widely used in the fieldof bio-analytical. Silver staining technique is an important method for signal amplification,It is widely used in the field of tissue sections stained protein, nucleic acid analysis anddue to its low cost, rapidity and high sensitivity.This study combines two methods for the detection of heavy metal ions-lead andcadmium, the dithizone colorimetric method and silver staining technology. It constructs alive semi-quantitative test strip which can simply, rapidly and sensitively detect ultra traceheavy metal ions-lead and cadmium in food and drinking. The study not only meets heavymetal ions-lead and cadmium on-site detection requirements of people and environment,but also provides an important basis with the heavy metal ions-lead and cadmium pollution prevention and control. And it has important significance for scientific researchand practical application. The main contents of this paper include:(1) Preparation of highly sensitive colorimetric sensor for detecting heavy metal ions, lead andcadmium. The preparation solutions of colorimetric sensor were explored to establish the bestpreparation programs. The highly sensitive colorimetric sensors of lead and cadmium wereconstructed with dithizone as chromogenic agent, cellulose acetate membrane as the basementmembrane. It was also called colorimetric strip, for the reason that the sensor of basementmembrane was composed of cellulose acetate membrane. We explored the preparationconditions of the test strip and the optimal conditions were established.(2) With silver enhancement technique, the detection of ultra trace lead and cadmium wasachieved by the colorimetric strip. Dithizone colorimetric could combine with lead andcadmium specificly, and formed PbS-CdS. This detection signal has been greatlyenhanced by PbS-CdS induced silver staining reaction. The images after silver stainingwere scanned by flatbed scanner, and the gray values were analyzed with software. Basedon the gray values, Pb2+-Cd2+concentration could be determined. In addition, theselectivity, sensitivity and feasibility of the test strip were verified through a series ofexperiments. And testing conditions were optimized. Under optimal conditions, theminimum visual detection limit of the test strip for lead and cadmium is1nM, and grayvalues showed a good linear relationship with Pb2+-Cd2+concentration from1×10-7M to1×10-9M.(3) Under the optimal conditions, lead and cadmium in the water samples were detectedby prepared test strips. The water sample was collected from Donghu Lake in Wuhan andwas suitably acidified. The results of our testing system was compared with ICP-MS’results and showed highly accordance.