Simultaneous Determination Of Lead And Cadmium In Water By Reduced Graphene Oxide-Modified Glassy Carbon Electrode With Mercury Film Deposition

Objective Lead is a toxic heavy metal element,widely used in automotive batteries,alloys,dyes and other fields.Lead can cause damage to the nervous system,cardiovascular system,reproductive system,etc.The International Agency for Research on Cancer（IARC）classified inorganic lead as a class 2A carcinogen.Cadmium is a highly toxic heavy metal element.With the mining and smelting of cadmium-bearing ores,the production and use of nickel-cadmium batteries,coatings,electroplating and cadmium alloys,a large amount of cadmium is discharged into the environment.Cadmium enters the human body mainly through the digestive tract and respiratory tract,and travels to all parts of the human body along with the blood.The kidney is the main target organ of cadmium.Long-term exposure to low dose cadmium can lead to chronic cadmium poisoning.Heavy metals can be deposited into the human body through the food chain,causing a variety of diseases and even cancer.In recent years,heavy metal pollution has attracted extensive attention,and people are increasingly concerned about personal health and environmental safety.To strengthen the monitoring and early warning of heavy metals in water is an important content of environmental monitoring in China,so it is necessary to establish a sensitive and rapid detection method.This study aims to establish a new method based on rGO-electrodeposited mercury film modified glassy carbon electrode for simultaneous detection of lead and cadmium in water,and to provide a more sensitive method for monitoring lead and cadmium in water.Methods（1）GO was reduced and deposited on the surface of glassy carbon electrode（GCE）by linear cyclic voltammetry（CV）.Then mercury（Hg）was modified on the surface of the electrode by electrodeposition to obtain a glassy carbon electrode（rGO-Hg/GCE）modified by rGO-Hg film.Lead and cadmium were detected simultaneously by electrochemical deposition and differential pulse voltammetry（DPV）.（2）In order to obtain better detection results,three conditions of deposition potential,deposition time and pH value of buffer solution were optimized.（3）Under the optimal experimental conditions,the methodological indexes such as linear range,detection limit,accuracy,precision and interference experiment were studied and discussed.（4）The proposed method was applied to the detection of lead and cadmium in actual water samples,and the results were paired with the results of GFAAS by t-test to verify the practicability and accuracy of the method.（5）The uncertainty introduced in the experiment is evaluated to determine the key links that affect the results.Results（1）According to the typical CV curves of GO reduction and the images of scanning electron microscope,it is shown that rGO has been successfully prepared.Compared with GCE,the peak current of CV of rGO/GCE increased,indicating that GO was successfully reduced and deposited on the electrode surface.Compared with GCE,rGO/GCE and Hg/GCE,the peak current value of Pb²⁺and Cd²⁺on rGO-Hg/GCE is significantly higher,and the peak shape is more symmetrical.The dissolution potential is about-0.54V and-0.70V respectively,indicating that rGO-Hg/GCE has been successfully constructed.（2）The results of the optimized detection conditions were as follows:the deposition potential was-1.2V,the deposition time was 360s,and the buffer pH was 4.5.（3）Under the optimal conditions,there was a good linear relationship between the peak current of lead and cadmium ions and their concentrations in the range of 1.0～50.0μg/L.The standard lead curve equation Y=0.0154X+0.0355,the correlation coefficient r=0.993,the detection limit was 0.73μg/L,the standard recovery was 95.8%～105.6%,the relative standard deviation was1.98%～5.01%.The standard curve equation Y=0.0256X+0.0163,the correlation coefficient r=0.998,the detection limit was 0.99μg/L,the standard recovery was90.9%～100.7%,and the relative standard deviation was 3.33%～5.71%.Common ions in the water(such as Na²⁺,Ca²⁺,Mg²⁺,Cl^-,etc.)have no influence on the peak shape and current value of lead-cadmium stripping peak,indicating that the method has good selectivity.（4）The concentrations of lead and cadmium in the wastewater samples tested ranged from 1.52 to 20.21μg/L and from 1.69 to 20.02μg/L respectively.The t test showed that there was no significant difference in the concentration of lead and cadmium measured by the method compared with the national standard method.（5）The uncertainty of the water samples with Pb²⁺and Cd²⁺concentrations 7.97μg/L and 8.31μg/L was evaluated,and the extended uncertainty was 0.50μg/L and 0.42μg/L.Conclusion（1）This study established a new method for simultaneous determination of lead and cadmium content in water based on Reduced graphene oxide（rGO）-electrodeposited mercury film modified glassy carbon electrode.（2）The combined action of rGO and Hg provides more reaction sites for the reaction,enhances the electron transport capability of the modified electrode surface,significantly improves the peak current value,and improves the detection sensitivity.（3）The method is simple in operation,low in detection limit,high in sensitivity,good in accuracy and selectivity,and can be used for simultaneous determination of lead and cadmium in different water samples.