A classical inhibition biosensor based on the glucose oxidase enzyme designed to determine zinc, lead, cadmium and mercury ions is described, characterised  and employed to be checked for each one of these heavy metal ions as well as to determine a ‘pool’ of metal ions in environmental aqueous matrices, i.e. river and sea waters. Experimental research was performed with special attention paid to the operating procedures for measurement and calculation. To this end, two alternatives to the classical procedure are proposed and discussed in order to shorten analysis time but without reducing analytical performances.