Study On The Rapid Determination Of Cadmium In Food By Catalytic Pyrolysis-atomic Absorption Spectrometry

With the rapid development of agriculture and industry in China,the pollution of agricultural environment has become more and more serious,and cadmium(Cd)has become the primary contaminant in agricultural soil.The traditional detection methods for Cd in agricultural products are mostly based on liquid injection atomic spectrometry,which has problems such as complicated sample pretreatment,cumbersome steps requiring chemical reagents,and cannot be used for emergency rapid detection.In this study,we developed an atomic absorption spectrometer(AAS)for solid injection analysis of Cd in foodstuffs with electrothermal evaporation(ETV)and catalytic pyrolysis as the core technologies,combined with a recyclable nitrogen and hydrogen gas generation system,and established a direct injection method for the rapid detection of Cd in foodstuffs.The results showed that the method is easy to operate,sensitive and does not require an external high-pressure gas source,and the analysis time is only 3 min.The main contents of this thesis and related research results are as follows.(1)Collaborated on the development of an integrated analysis tube to build the ETV-AAS instrument system.Using air as the source of oxygen and nitrogen,the mixture composition is controlled by a hydrogen generator,enabling precise control of the air or nitrogen-hydrogen mixture,thus eliminating the need for the previously commonly used external argon-hydrogen high-pressure gas cylinder.The ETV,catalytic pyrolysis and transfer line(integrated outlet tube)are integrated into an integrated analysis tube.The ETV-AAS instrument system was assembled by using Ni Cr wire as an electrothermal evaporator for ashing and evaporation of Cd;kaolin as a high temperature filler for catalytic pyrolysis for adsorption of interfering substances and pre-trapping and rapid transport of Cd;a high temperature integrated outlet tube for Cd transport and nitrogen-hydrogen flame atomization,and AAS as a detector.(2)Optimization and basic performance testing of the ETV-AAS instrument system parameters.The drying ashing,electrothermal evaporation,hydrogen flow rate and catalytic furnace conditions of the instrument system were optimized using a nickel boat injection,and the results showed that the air injection condition of 300 m L/min and drying and ashing times of 20 s and 55 s,respectively,could achieve effective ashing of the sample and pre-capture of a small amount of evaporated Cd,;when switched to a hydrogen flow rate of 300 m L/min the formation of a reducing nitrogen-hydrogen mixture atmosphere can release the Cd in the sample residue rapidly and merge it with the pre-captured Cd into the collimation tube for AAS determination.Preliminary matrix interference test results showed that common inorganic elements and organic matter in foodstuffs did not interfere significantly with this instrument.Under the optimal conditions,the limit of detection(LOD)of ETV-AAS was 0.2 ng/g,the linear range of the instrument was 0?200ng,the linear regression coefficient(R~2)of the standard curve could reach above 0.998,and the relative standard deviation(RSD)of the standard solution was below 6%.(3)The ETV-AAS assay for the rapid detection of Cd in food was established and validated with the confirmatory method.In this study,grain,vegetable,tea and meat were selected as the main food samples,and the conditions of drying ashing,electrothermal evaporation,hydrogen flow rate and catalytic furnace temperature of the ETV device were optimized for the real samples.Under the optimal instrument parameters,the LOD of this method was 0.1 ng/g and the method LOQ was 0.3 ng/g when the injection volume was 0.2 g,which can meet the requirements of most of the Cd contents in food products in the market.The spiked recoveries of multiple sample matrices were in the range of 98.8%?105%,and the RSDs of sample determination were in the range of 1.1%?11%with good stability.By comparing the signals of standard solutions and food samples with the same Cd content,it was found that the signal peak shapes were basically the same,indicating no significant matrix interference.Based on the above study,the method established in this study can be used for the determination of a variety of real food samples.Since the solid direct injection analysis does not require sample digestion treatment,the whole instrumental analysis time can be controlled to about 3 min,indicating that the method established in this study can determine the Cd content in foods rapidly and accurately.