(BiFE), mercury film (MFE) and bare

(BiFE), mercury film (MFE) and bare glassy carbon electrodes
for the measurement of 100gL
−1
tin, and the effect upon the
stripping signal if tin was added before (A) or after the addition
of catechol (B). In both cases, there was practically no signal
corresponding to tin observed at the bare GCE. The addition
of tin before catechol (A(b)) revealed well-defined single sig-nals in both recorded stripping voltammograms obtained at in
situ formed MFE and BiFE, at−0.60 and−0.59 V, respectively.
However, both electrodes exhibited relatively low signals corre-sponding to tin, with the signal at BiFE approximately twice as
large as that observed at MFE. Following addition of 150M
catechol to the measurement solution (A(c)), the signals for tin at
both MFE and BiFE increased significantly. It can be clearly seen
that the increase in the stripping signal is more pronounced at
BiFE and is accompanied with the appearance of a second oxida-tion peak at−0.34 V, corresponding to stepwise oxidation of Sn
0
to Sn
2+
and Sn
2+
to Sn
4+
, respectively, while the absence of the
second peak is obvious at MFE. In the case where catechol was
added to the measurement solution before tin (B(b)), there was
practically no change in the stripping voltammograms recorded
at both MFE and BiFE electrodes in comparison with the solu-tion containing only 10 mg L
−1
of bismuth or mercury ions,
indicating the appropriateness of catechol for performing anodic
stripping voltammetry at in situ formed BiFE. After addition of
100gL
−1
tin (B(c)) to the solution (following the addition of
catechol), both electrodes exhibited two distinct voltammetric
stripping signals corresponding to stepwise oxidation of tin, the
signal at MFE (at−0.57 V) being higher than that observed at
BiFE (also at−0.57 V). However, it is important to note that in
both cases, when tin was added before (A) and after (B) addition
of catechol, the signals corresponding to tin at BiFE remained
practically unchanged (slightly higher, when tin was added after
catechol), while the signals obtained at MFE were consider-ably higher if catechol was added first. Concerning practical
application, this characteristic suggests that the BiFE is more
convenient and reliable for measurement of tin, particularly in
real samples, since tin is already present in the sample solution,
and pre-treatment of the electrode in a blank solution containing
only mercury ions and catechol can be tedious. Nevertheless,
non-toxic character of BiFE also favors its wider application
instead of mercury analogues.
To gain more insights into the effect of catechol upon the in
situ formation of BiFE, we conducted cyclic voltammetric mea-surements in a model solution of 0.1 M acetate buffer, to which
catechol was first added, followed by the addition of 10 mg L
−1
bismuth ions (Fig. 2A), and inversely, with the addition of