FAST AMPEROMETRIC FIA PROCEDURE FOR HEAVY METAL DETECTION USING ENZYME INHIBITION

Abstract

The inhibition effect of heavy metals ions such as Hg(II), Cu(II), V(V), and Ni(II) on the activity of oxidase enzymes such as alcohol oxidase, glycerol 3-P oxidase, and sarcosine oxidase has been studied and used for the construction of calibration curves in flow-injection analysis. A platinum-based H₂O₂ probe was used to measure the enzymatic activity of the selected oxidase enzymes. The most sensitive detection system was obtained using the glycerol 3-P oxidase/Hg(II) couple. A calibration curve was obtained in the 0.05–0.4 ppm range, with a detection limit of 0.05 ppm, and a 50% of inhibition (I₅₀) of 0.2 ppm. The enzyme alcohol oxidase was used to construct calibration curves for Cu(II) and V(V). The detection limits were 2 and 0.5 ppm, respectively, with I₅₀ ppm for cu(II) and 2.7 ppm for V(V). Ni(II) was detected in the 1–6 ppm range, using the enzyme sarcosine oxidase; I₅₀ was 3.8 ppm. Relative standard deviations were ≤5% for each enzyme/ion metal couple. The analytical behavior was comparable to measurements in batch analysis.

The analysis time was in the range of 10–15 minutes, which makes the system suitable for fast analysis of heavy metals in the 0.1–10 ppm range. The method could be usefully adopted as “on-line control” or “screening field-test” for contaminated water samples (typically industrial effluents) according to the detection limits. This will reduce the number of samples to be analyzed by standard methods based on AAS or ICP/MS detection.

Keywords:

• Heavy metals
• FIA
• Amperometric detection
• Enzyme inhibition

ACKNOWLEDGMENTS

The authors wish to thank the ENEA for financial support. A.S.L. thanks the Tempus/Socrates project for the Fellowship received.