sbornik_s_2011.pdf

XI. Workshop of Physical Chemists and Electrochemists´11 Brno
reduction and 1 oxidation peak on mercury electrodes 0. Nowadays, due to the toxicity of
liquid mercury, new non toxic electrode materials are still looked for. RF has been
successfully determined using glassy carbon electrode 0, modified gold electrode 0 or
diamond electrode 0.
The m-AgSAE is one of the modifications of silver solid amalgam electrodes, which
were introduced by Novotný and Yosypchuk in 2000 0. These electrodes are made from
non toxic silver amalgam and have been successfully used for voltammetric determination
of various compounds. This paper has been focused on application of mercury meniscus
modified silver solid amalgam electrode for voltammetric monitoring of riboflavin
reduction and its determination in pharmaceuticals.
8. EXPERIMENT
The stock solution of RF had to be stored in the dark and all analysis had to be
provided in a covered polarographic cell due to the light instability of RF. All
measurements were provided by computer controlled Eco-Tribo Polarograph PC-ETP in
3-electrodes set up (m-AgSAE or HMDE as a working electrode, saturated argentchloride
as a reference and platinum wire as an auxiliary electrode). DPV with optimized
parameters (Ein = 100 mV, Efin = -800mV, v = 20 mV.s -1 Eacc= 100 mV, tacc depends on
concentration of RF, height of pulse -50 mV, width of pulse 80ms) was found as a suitable
method for RF determination. The optimal conditions for the m-AgSAE`s surface
regeneration was found as 30 potential jumps between 0 and -1500 mV.
9. RESULTS AND DISCUSSION
It was found that RF provides 1 reduction and 1 oxidation peak on m-AgSAE as well
as on HMDE in wide range of pH (3-12), which consists with literature 0,0. The highest
reduction response on both used working electrodes was observed in medium of pH 5 that
is why the 0.05M acetate buffer of pH 5 was used for all subsequent analysis. It was also
found, using direct current voltammetry, that heigh of the reduction peak increased
linearly with the scan rate, which shows that the reduction is realized in adsorbed state.
Some statistical parameters were determined for the reduction of RF. The relative
standard deviation of 11 repeated measurements was calculated as RSDM(11) = 2.73 % (m-
AgSAE) resp. 1.36 %(HMDE). The relative standard deviations of 5 repeated
determinations were calculated for various concentrations levels using ADSTAT 0 (Tab.
1). The limit of detection is equal to 4.89×10 -9 (tacc = 5 s) for m-AgSAE and 5.16×10 -10
(tacc = 120 s) for HMDE. The linear dynamic range was found as 1×10 -8 to 1×10 -6 for m-
AgSAE and 2×10 -9 to 1×10 -6 for HMDE. The example of concentration dependence
obtained on m-AgSAE is shown in Fig. 2.
Tab. 1: Comparison of relative deviations and relative standard deviations of repeated
determinations obtained on m-AgSAE and HMDE
Added
[M]
5×10 -8
m-AgSAE HMDE
Found RD RSDD(5) Added Found RD RSDD(5)
[M] [%] [%] [M] [M] [%] [%]
4.95×10 -8 -1 0.65 1×10 -8 1.04×10 -8 +4 3.65
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