3.5. Effect of salt addition
The salt addition into aqueous samples can improve significantly the
extraction of several analytes using DLLME. The addition of electrolytes
to the solution causes a greater solubility of analytes in the organic
phase, increasing the extraction efficiency [24–26]. The salt amount
(as NaCl) added to the sample was evaluated ranging from 0 to 10%
(m/v). Ten milliliters of sample (with suitable dilution) was used
followed by addition of 500 μL of DDTC and NaCl solutions. For Cu,
the salt addition did not increase the signal and its addition was
not required. However, using 5% NaCl solution, the signal for Fe extraction
was increased (results not showed). Thus, only for Fe extraction, it
was necessary the addition of 500 μL of 5% NaCl solution previously to
the extraction