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M. FE DE LA TORRE Y COLS. AN. R. ACAD. NAC. FARM.

Cu(II) at 280 nm was observed, possibly due to the formation of
complexes between this cation and the EDTA. The presence of 2%
SDS restores the behaviour of the system for the concentrations
tested (data not shown).

FIGURE 8. Variation in the A280 of Cu(II) in the presence of PPi, and
interferences produced by the presence of 5% SDS or 50 mM Na3PO4. The
blank contained 0.5 mM CuSO4 and 10 mM Na4P2O7 in 100 mM AMPSO/NaOH,
pH 9.4, at 37º C. The continuous line corresponds to the best fit in the absence of
interferences. The broken lines delimit the margins of confidence for 95% of the
curve. The presence of 5% SDS ! or 50 mM Na3PO4 ! did not significantly
change the behaviour of the system (P > 0.05), which can be described by the

same empirical equation.

Interference by nucleotides

The influence of nucleotides in the medium at concentrations of
1.0 and 5.0 mM was studied using ATP. The presence of ATP
decreases the absorbance of Cu(II), possibly by forming complexes
with the polyphosphate tail. The addition of SDS 2% allowed this

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