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

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 μl 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 ⩽ 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.