An enzymatic procedure for the determination of mercury(ii) is described, based on inhibition of invertase using glucose oxidase and catalase co-immobilised on controlled-pore glass (CPG) coupled to a thermometric continuous-flow sensor system to follow the invertase activity. A small amount of invertase (0.66 U ml(-1)) was incubated for a short time in sucrose solution and 20 mul of the mixture were injected into the enzyme thermistor system to give a temperature change corresponding to 100% enzyme activity. Addition of a mercury(II) sample to the mixture caused a decrease in the invertase activity, that allowed the determination of mercury(II) concentrations in the 5-80 ppb range with RSD less than or equal to 0.74%. The analysis time was 2-6 min including incubation. The main advantages of this thermometric biosensor assay are as follows: simplicity, with no need for regeneration due to the use of a cheap, soluble sensing enzyme; robustness, with excellent reproducibility and repeatability; and long operational and storage stability of the enzymes involved in the detection system.
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