Formation of diphenylethylenediamine/sodium dodecyl sulfate/Na2CO3 aqueous two-phase system and its response and selectivity towards aromatic amino acids

Developing a simple and effective method for detecting and separating amino acids has practical significance. Aqueous two-phase system (ATPS) has the advantages of mild preparation conditions, good stability, and high biocompatibility. In this study, an ATPS exhibiting distinct responses and selectivity profiles toward Phe, Trp, and Tyr was constructed using (1S, 2S)-(-)-1,2-diphenylethylenediamine (DPED), sodium dodecyl sulfate (SDS), and sodium carbonate (Na₂CO₃). It is found that the amino acids can trigger the transformation of the DPED/SDS/Na₂CO₃ ATPS into a single-phase system, but the critical concentrations required for this phase transition vary significantly among the amino acids: Phe and Trp induce the transition at very low concentrations, whereas Tyr requires a much higher concentration (8–13 times greater than Phe and Trp under optimal conditions). This stark contrast enables the DPED/SDS/Na₂CO₃ ATPS to serve as a sensitive and visually distinguishable platform for differentiating Tyr from Phe and Trp. Moreover, the DPED/SDS/Na₂CO₃ ATPS exhibits selective phase partitioning: Phe and Trp preferentially concentrate in the top phase, while Tyr predominantly distributes into the bottom phase. This distinct partitioning behavior allows for the efficient separation of Phe and Trp from Tyr, highlighting the system’s dual functionality for both detection and purification of Tyr from Phe and Trp. These findings indicate the potential of using this system to develop methods for separating and detecting the amino acids.