Sulfite induced autoxidation of Ni(II), Co(II) and Cu(II) / tetra, penta and hexaglycine complexes. Chemiluminescent determination of S(IV) and acetaldehyde / Autoxidação dos complexos de tetra, penta e hexaglicina de Ni(II), Co(II) e Cu(II) induzida por S(IV). Determinação de S(IV) e aldeídos por quimiluminescência

AUTOR(ES)

Luciana Batista de Carvalho

DATA DE PUBLICAÇÃO

2007

RESUMO

The autoxidation of Ni(lI) and Co(lI) complexes with tetra, penta and hexaglycine, in borate medium, is accelerated by sulfur (IV) species (H2S03, HS03- and SO32-). The formation of Ni(llI) and Co(lIl) complexes was followed spectrophotometrically at 325 and 265 nm, respectively. The autoxidation rate of Ni(II)/Gn complex increases with S(IV) concentration and is maximum at pH ~ 8.5. The process is autocatalytic with Ni(lIl) or Co(llI) acting as initiators, formed by spontaneous oxidation by oxygen. The dependence of the observed rate constant with S(IV) concentration showed evidences of back or parallel reactions with formation of mixed ligand complex prior to the oxidation step. The autoxidation of Cu(II)/penta and hexaglycine complexes at pH = 9, in the presence and absence of S(IV), is very slow. The presence of S(IV) and of small amounts of Ni(lI) or Co(lI) increases significantly the effectiveness and reaction rate (induction period = 0.5 s). The mechanism involves a radical chain and redox cycling of the metal íon complexes. Acetaldehyde and formaldehyde partially inhibit the autoxidation reaction of Ni(II)/G4 in the presence of S(IV) and luminol. The developed chemiluminescent method can be used for determination of formaldehyde [(5.0.10-5 - 1.0.10-2) mol L-1] and acetaldehyde [(1.0.10-4 - 0.10) mol L-1), being not possible their isolated detection. The S(IV) induced autoxidation of Ni(OH)2 in the presence of luminol, occurs with radiation emission, allowing S(IV) detection in the range 5.0.10-8 to 1.0.10,-5 mol L-1, with detection limit of 1.3.10-8 mol L-1.

ASSUNTO(S)

cobre(ii) nickel(ii) copper(ii) cobalt(ii) sulfite espectrofotometria spectrophotometry níquel(ii) sulfito cobalto(ii)

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