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VOL. 72 (3), 463-487, 2006 SPECTROPHOTOMETRIC CHARACTERISATION OF THE...
Both PPi and Pi interact with Cu(II) in solution and modify its
absorption spectrum in a concentration-dependent fashion (Fig. 1).
The presence of both Pi and PPi increase the absorbance of Cu(II)
in solution with a maximum at ca 250 nm. The presence of PPi
decreases the absorbance of Cu(II) with a minimum at ca 290 nm.
The wavelength of 280 nm was chosen for the assay in order to avoid
interferences due to the presence of organic molecules, mainly
aromatic rings and nitrogenous bases. The aim of this was to
minimize the matrix effects in the sample when comparing one
measurement with a calibration curve prepared with standards.
FIGURE 1. Influence of pyrophosphate and orthophosphate on the absorption
spectrum of Cu(II). All determinations were carried out at pH 9.4 and 37ยบ C.
The blank was a solution 0.5 mM of CuSO4 in water. The continuous lines
correspond to the spectra of 0.5 mM CuSO4 with 1, 0.5 and 0.1 mM Na4P2O7
respectively for a, b and c. The broken line d corresponds to the spectrum of
0.5 mM CuSO4 with 10 mM Na3PO4. Formation of the Cu(II)-PPi complex
decreased the absorption of Cu(II): it was minimum at 290 nm. Formation of the
Cu(II)-PPi and Cu(II)-Pi complexes increased the absorption of Cu(II): its
maximum was seen at 250 nm.
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