3.4. Concentration of chelating agent
As previously mentioned there is a strong relationship between the
pH and the interaction between analyte and chelating agent. Taking
into account that DDTC is not a selective reagent, it is necessary to select
a sufficient amount of this reagent to assure the complexation of analyte
[22,23]. It is important to mention that several elements are present in
wine samples and they could be extracted (even that unintentionally)
within the analyte. Once all optimization was performed using red
wine, probably all competing elements were also complexed and an
evaluation of interfering ions was not required. The effect of DDTC was
evaluated varying its concentration from 0 to 2% (m/v) solution. In this
case, 10mL of sample (with suitable dilution)was used followed by addition
of 500 μL of DDTC solution. The best results (not showed) were
obtained using 1.5 and 1% DDTC solution for Cu and Fe complexation,
respectively.