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M. FE DE LA TORRE Y COLS. AN. R. ACAD. NAC. FARM.
A280,tot=eCu’ ([Cu]’sample-[Cu]’blank) + eCuP2O72([CuP2O72–]sample-[Cu(P2O7)26–]blank+[Cu(P2O7)26–]sample-[CuP2O72–]blank)
FIGURE 6. Correspondence between expected and real behaviour for the
Cu(II)/PPi system. Plotting of the experimental (!) and calculated (', dotted
line) values of A280 for the addition of PPi, with [Cu]tot = 0.50 mM, and containing
the blank 0.50 mM CuSO4 10.0 mM Na4P2O7 in 100 mM AMPSO/NaOH pH 9.4
at 37º C.
where the values of the concentrations of the absorbent species are
[Cu]’blank = 4.14e-5, [CuP2O7]blank = 2.38e-4 and [Cu(P2O7)26–]blank = 2.21e-4.
Owing to the impossibility of finding an easy mathematical
expression affording A280 as a function of [PPi]tot we decided to
describe the behaviour of the system by means of an empirical
equation. The simplest expression providing the best fit with a
minimum number of parameters was a modified hyperbolic decay:
A280 = p(1) [PPi]tot + p(2) p(3)
p(3)+ [PPi]tot
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