Partitioning of salicylic and acetylsalicylic acids by aqueous two-phase systems : mechanism aspects and optimization study.

Abstract

Emerging contaminants such as drugs and pharmaceuticals have attracted attention in recent years due to their adverse effects in humans and the environment. They are difficult to monitor, since they are present at very low concentrations in environmental matrices. Acetylsalicylic acid (ASA) and salicylic acid (SA) are the most highly consumed drugs worldwide. In this investigation, an extensive study of acetylsalicylic acid and salicylic acid partitioning was carried out in aqueous two-phase systems (ATPSs) formed by a polymer, salt, and water. In the univariate analysis, the length of the tie line and the nature of the polymer and electrolyte that form the ATPS were found to have strong effects on the partition coefficients (K) of ASA and SA, while pH had a significant effect on the partition coefficient of ASA only. In all conditions, the analytes partitioned preferentially to the top phase (K >>1), indicating a preferential interaction of the analytes with the components of this phase. A multivariate study of the optimal SA partition conditions was carried out through a central composite design, showing that the optimal ATPS for SA partitioning is composed of [PEO1500] = 29.06 %wt and [Li2SO4] = 11.94 %wt at pH 6.1. Under these optimal conditions, the expected value for K is ±940. Eight replicates of this system reported a real value of K = 949 (±47). Thus, the ATPS was demonstrated to be an efficient system for the extraction of SA and ASA, with high K values.