Metallothionein Isoforms For The Selective Biosorption And Preconcentration Of Cadmium At Ultra-trace Level

Metallothioneins(MTs)are a class of low molecular weight cysteine-rich metal-binding protein which are widely presented in the organism and have binding characteristics with certain heavy metals.It is clear that MTs can be used for the enrichment,removal and recovery of a certain precious metals.Cadmium is the third-largest toxic heavy metals only to mercury and plumbum,leading the threat of environment pollution and human health,and excessive intake or excessive contact will be serious harm to human and animal health.Therefore,finding appropriate separation and enrichment of trace cadmium and detection methods is very important scientific content for the environment and humans.Two isoforms of MT,e.g.,metallothionein isolated from rabbit liver(rMT)and recombined cyanobacteria metallothionein(SmtA),were immobilized on spherical SiO2 particles to evaluate their biosorption behaviors for cadmium.We found that effective sorption is achieved at pH 6.0-10.0 and cadmium binding on both MT isoforms follows Langmuir adsorption,and their adsorption dynamic fits pseudo-second-order kinetics model.SmtA exhibits a higher cadmium sorption capacity than rMTs both statically and dynamically.SmtA exhibits a higher cadmium sorption capacity and the cadmium retained on SmtA surface was recovered with a small amount of thiourea in nitric acid and quantified with graphite furnace atomic absorption spectrometry(GFAAS).A method employing SmtA@SiO2 as sorption medium for the on-line highly selective separation/preconcentration of trace cadmium with detection by GFAAS was thus developed.With a sample volume of 1 mL and an eluate volume of 50?L,an enrichment factor of 13.8 is obtained.Under the optimal conditions,accurate determination of cadmium in the range of 5-100 ng L-1 could be achieved,along with a limit of detection of 1.4 ng L"1 and a RSD of 3.2%(n=7,50 ng L-1).This procedure is validated by analyzing cadmium in certified reference materials,achieving satisfactory agreements between the certified and the obtained values.Spiking recoveries are also performed by using a series of environmental water samples.