For CPE from acid digests, on-line neutralization was exploited to induce phase separation without an external heating device. Sodium hydroxide concentration was defined to yield an amount in the sample zone slightly lower than the acid from the sample, aiming at a partial neutralization and heat release. The neutralizing solution contained also NaCH3COO aiming at on-line formation of a buffer with a pH suitable for complex formation. By taking into account these aspects, concentrations were defined as 1.4 mol L−1 NaOH and 1.6 mol L−1 NaCH3COO. This solution (R2) was handled by an additional micro-pump (Fig. 1, P4) and pH 5.5 was achieved in the sample zone with one pulse of P4 per sampling cycle, which corresponds to 80 μL of R2 in the sample zone. This pH was suitable for complex formation, which was maximum within pH 4.5 and 6.0 due to the compromise between protonation of the ligand and metal hydrolysis. This value is in agreement with that observed in previous studies [23] and [24].