Green And Safe Pretreatment Technology For Detection And Analysis Of Heavy Metal Ions In Food Solid Samples Based On Ionic Liquids

Heavy metals,as ubiquitous environmental pollutants,pose a great potential hazard to food safety and are food contaminants strictly controlled,so detection and analysis of heavy metal ions in food solid samples is important.Before detection and analysis of heavy metal ions in food solid samples,pretreatment of food solid samples is needed.The wet digestion is now the most widely used pretreatment technology.However,large amounts of acid solutions are used during the wet digestion,which are harmful to the health of the inspectors and cause certain pollution to the environment.This work is to develop a green and safe pretreatment technology for detection and analysis of heavy metal ions in food solid samples based on ionic liquids.A new green,safe and fast pretreatment technology was established to determine the content of Pb,Cd and Cr in such typical food solid samples as dried fungus,dried shiitake mushroom and dry tea based on the fact that they could easily and fast dissolved in ionic liquid1-butyl-3-methyl imidazole chloride?[Bmim]-Cl?.Firstly,the content of Pb,Cd and Cr in ionic liquid[Bmim]-Cl from three different factories was determined by graphite furnace atomic absorption spectrometry to evaluate whether it could be directly used as a solvent for pretreatment process.The results showed that the ionic liquid[Bmim]-Cl from some factories had high content of Pb,Cd and Cr and it could not be directly used as a solvent for pretreatment process.To remove such heavy metals as Pb,Cd and Cr,some dissolved sulfides were added to the ionic liquid[Bmim]-Cl under alkaline conditions and then filtered the obtained solution with a0.22?m microporous membrane.This method could effectively remove such heavy metals as Pb,Cd and Cr in the ionic liquid[Bmim]-Cl and the obtained ionic liquid[Bmim]-Cl could be used as a solvent for pretreatment process.Then a spike test on the aqueous solution of ionic liquid[Bmim]-Cl was performed by graphite furnace atomic absorption spectrometry according to the temperature programmed conditions in the current national standard.It was found that the ionic liquid[Bmim]-Cl had different degrees of inhibition on the determination signals of Pb,Cd and Cr.Addtion of HNO₃to the aqueous solution of ionic liquid[Bmim]-Cl and optimization of ashing temperature could effectively elimilate this inhibition.For the determination of Pb,when the concentration of ionic liquid[Bmim]-Cl in its aqueous solution was 0.06g/m L,the concentration of HNO₃ was above 4.08%,and ashing temperature was 600?,the interference of ionic liquid[Bmim]-Cl on Pb detection could be eliminated.For the determination of Cd,when the concentration of ionic liquid[Bmim]-Cl in its aqueous solution was 0.06 g/m L,the concentration of HNO₃ was above 6.8%,and ashing temperature was 650?,the interference of ionic liquid[Bmim]-Cl on Cd detection could be eliminated.For the determination of Cr,when the concentration of ionic liquid[Bmim]-Cl in its aqueous solution was 0.06 g/m L,and ashing temperature was 1300?,the interference of ionic liquid[Bmim]-Cl on Cr detection could be eliminated.Because the ashing temperature during determination of Pb,Cd and Cr in samples was relatively high,the equal amount of 2%phosphate was needed as matrix modifiers.Finally,the pretreatment conditions for such typical food solid samples as dried fungus,dried shiitake mushroom and dry tea were optimized and the content of Pb,Cd and Cr was determined by graphite furnace atomic absorption spectrometry.The optimized pretreatment conditions were to dissolve 0.3 g sample with concentrated 0.5m L HNO₃ and 3 g ionic liquid[Bmim]-Cl,the dissolution time was 2 min?5 min,and the heating temperature was 160?.Under these optimized pretreatment conditions,Experiments of detection for Pb,Cd and Cr showed favorable accuracy,their recovery reached 90.66%?115.133%,the detection limit of Pb was 0.685?g/L,the detection limit of Cd was 0.209?g/L,and the detection limit of Cr was 0.145?g/L.Compared with the wet digestion,this pretreatment technology could shorten the pretreatment time by 36-48times,and reduce the amount of acid solution was by 12-20 times.It was a green,safe and fast pretreatment technology for detection and analysis of heavy metal ions in food solid samples.