Flow injection analysis of mercury(II) based on enzyme inhibition and thermometric detection

An enzymatic procedure for the determination of mercury(ii) is described, b ased on inhibition of invertase using glucose oxidase and catalase co-immob ilised on controlled-pore glass (CPG) coupled to a thermometric continuous- flow sensor system to follow the invertase activity. A small amount of inve rtase (0.66 U ml(-1)) was incubated for a short time in sucrose solution an d 20 mul of the mixture were injected into the enzyme thermistor system to give a temperature change corresponding to 100% enzyme activity. Addition o f a mercury(II) sample to the mixture caused a decrease in the invertase ac tivity, 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 bio sensor assay are as follows: simplicity, with no need for regeneration due to the use of a cheap, soluble sensing enzyme; robustness, with excellent r eproducibility and repeatability; and long operational and storage stabilit y of the enzymes involved in the detection system.