Desenvolvimento de procedimentos analíticos limpos para a determinação de cloreto e demanda química de oxigênio em águas.
Fecha
2004-12-17Autor
Silva, Claudineia Rodrigues da
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The work here described deals with the development of clean analytical methods for
determination of chloride and chemical oxygen demand in water samples.
A flow injection spectrophotometric method was developed for
determining chloride in water samples based on a solid phase reactor (SPR)
containing Hg(SCN)2. The solid reagent was immobilized in epoxy resin. The solid
phase reactor was regenerated using an intermittent flow of a solution containing
0.12% m v-1 Hg(SCN)2 and this strategy was needed for baseline stabilization. The
analyte chloride displaces thiocyanate from the SPR and this latter reacts with Fe(III)
forming a red complex measured at 480 nm. The lifetime of the reactor was
estimated in 1000 injections, and both the reagent consumption and the waste
generation were appreciably reduced. The obtained results were in agreement with a
standard method at a 95% confidence level. The relative standard deviation was
2.25% for 10 successive injections of a 8.0 mg L-1 Cl- solution, and the analytical
frequency was 100 determinations h-1.
Two metallic electrodes, copper and nickel, were built for determination
of chemical oxygen demand (COD). The copper electrode was used in voltammetric
measurements in the 0.25 to 0.70 V potential range (vs. Ag/AgCl). The analytical
curves were obtained using reference solutions containing from 477 to 2800 mg L-1
glucose.The detection limit was estimated in 152 mg L-1 and the relative standard
deviation was < 0.5% (n = 4) for a sample containing 2800 mg L-1 glucose.
Voltammetric measurements for COD determination using the Ni
electrode were made in the potential range of 0.25 to 0.50 V (vs. Ag/AgCl). The
analytical curve was obtained using solutions containing from 48 to 469 mg L-1 of
COD. The detection limit was estimated in 7.7 mg L-1 and the relative standard
deviation was <2.0% (n = 3) for a sample containing 469 mg L-1 glucose.
The voltammetric methods employing Cu/CuO e Ni/NiO electrodes
were applied for COD determination in residual waters of food industry and the
obtained results were compared with those obtained using a standard method. The
conventional methods are usually based on toxic reagents and the time of analysis is
around 4 h. The residual solution is either stored or its discard is expensive. The
main advantage of the proposed voltammetric methods is that no toxic reagent is
used and the time of analysis is shorter, i.e. around 30 min.