Bacterial sensors based on Acidithiobacillus ferrooxidans: Part II. Cr(VI) determination

The aerobic acidophilic bacterium Acidithiobacillus ferrooxidans oxidizes Fe2+ and S2O32− ions by consuming oxygen. An amperometric biosensor was designed including an oxygen probe as transducer and a recognition element immobilized by a suitable home-made membrane. This biosensor was used for the indirect amperometric determination of Cr2O72− ions owing to methods based on a mediator (Fe2+) or titration.Using the mediator, the biosensor response versus Cr2O72− was linear up to 0.4 mmol L−1, with a response time of, respectively, 51 s (2 × 10−5 mol L−1 Cr2O72−) and 61 s (6 × 10−5 mol L−1 Cr2O72−). The method sensitivity was 816 μA L mol−1. Response time and measurement sensitivity depended on membrane material and technique for biomass immobilization. For example, their values were 90 s—200 μA L mol−1 when using a glass-felt membrane and 540 s—4.95 μA L mol−1 with a carbon felt one to determine a concentration of 2 × 10−5 mol L−1 Cr2O72−.For the titration method, the biosensor is used to determine the equivalence point. The relative error of quantitative analysis was lower than 5%.