Abstract:
Trace metals play important roles in biological and ecological systems. In biology,
trace metals act as catalytic or structural cofactors and regulate biochemical
processes. In the environment, natural and anthropogenic sources of trace metals
mobilized into natural waters where they can create harmful and persistent pollution.
Trace metal chemistry in physiological and environmental systems can fluctuate
rapidly which makes it difficult to clearly define trace metals’ roles in these systems
with traditional analytical methods. Furthermore, these systems are often chemically
harsh and physically delicate (e.g. the brain), factors that add to the challenge of
analysis in real systems. Fast scan cyclic voltammetry (FSCV) is explored in the
context of rapid, minimally invasive and robust analysis of Cu2+ in aqueous samples
with carbon fiber microelectrodes (CFMs). Unique Cu2+-specific waveform was
generated with an optimized potential window and scan rate to provide sub-second
analysis of Cu2+. An array of electrochemical and spectroscopic techniques was
employed to discover the underlying mechanisms of the ultra-fast FSCV response.
Adsorption was explained as the fundamental mechanism for the rapid FSCV signal
and the thermodynamic properties of adsorption of Cu2+ onto CFMs were evaluated
with fast scan controlled adsorption voltammetry (FSCAV) in different matrices.
In aquatic systems and soils, metals commonly exist in complexed forms with
organic and inorganic ligands. It is generally the free, unbound metal that is the most
toxic, thus metal speciation is a critical factor when considering metal pollution. Free
Cu2+ concentrations and the solution formation constant (Kf), provide valuable
speciation information. We show that FSCV and FSCAV can be utilized to study
copper speciation. Mathematical relationships (Equation 1) were constructed from
experimental data to predict free Cu2+ concentrations and the overall Kf of a solution
with a range of model ligands, representing a range of Cu2+- ligand Kf expected to be
encountered naturally. These findings showcase the power of FSCV as a real-time
biocompatible, eco-friendly speciation sensor with excellent sensitivity and a
temporal resolution of milliseconds.
Equation 1:
log10(Kf) = 12.21 – (5.49 x 107) x [Cu2+]free + (0.12) x Current + (1.74 x 105) x
[Cu2+]free
2 x Current + (8.82 x 1011) x [Cu2+]free
2 – (4.21 x 10-4) x Current2
