Cr(VI) quantification using an amperometric enzyme-based sensor: interference and physical and chemical factors controlling the biosensor response in ground waters

The development of an amperometric enzyme-based sensor for chromate (CrO(4)(2-)) quantification in ground waters was investigated. Crucial physical and chemical factors characterising ground waters were tested for their influence or interference on chromate quantification: pH (7.6-8.5), temperature (9-25 degrees C), ionic strength (0-0.2M), oxygen, metals, bicarbonate and sulphate. The biosensor's response was dependent on temperature and pH as sensitivity increased with temperature and was higher at pH 7.6 than at pH 8.5. Sensitivity decreased with ionic strength until 0.1M, and was stable for higher values. Dissolved oxygen did not allow chromate quantification when it was present, but O(2) could be eliminated by adding Na(2)SO(3) or bubbling nitrogen gas into the solution. Bicarbonate did not interfere with chromate quantification by the biosensor. Sulphate was detected with a detection threshold 80 times higher than that of chromate and a lower sensitivity. Several metals (V(V), W(VI), Mn(VII), Mo(VI)) similar to chromate due to their oxidative properties and structure (oxyanions) were tested as possible interfering compounds. The sensitivity of the biosensor for these metals was low and the detection level was 30 times higher than that of chromate. These metal concentrations are usually weaker than chromate concentration in polluted ground waters so that dilution of the sample should allow chromate quantification by the biosensor. This study shows that the cytochrome c(3)-based sensor can detect compounds other than chromate but with a lower sensitivity. Although non-specific for the detection of chromate, it can however be adapted and used for the quantification of chromate in ground waters containing low sulphate concentration.