Stability of clavulanic acid in PEG/citrate and liquid–liquid extraction in aqueous two-phase system

β-Lactamases are enzymes responsible for the hydrolysis of β-lactam antibiotics, being produced by several pathogenic bacteria. Clavulanic acid is a commercially and clinically important β-lactamase inhibitor, its extraction being possible by the application of aqueous two-phase system. In this study, clavulanic acid stability was investigated at different molar mass PEG (400, 1 000 and 20 000 g mol−1) and at different citrate concentrations (5 and 20%) PEG/citrate aqueous-two phase systems (ATPS), under different pH values (4.0–8.0). Clavulanic acid extraction was also evaluated. Low citrate concentration and PEG 20 000 (g mol−1) ATPS, at pH 6.0, were shown to be the systems that presented the highest clavulanic acid stability. Based on this, a factorial design 22 was used to evaluate CA extraction, being PEG (20, 25 and 30%) and citrate (5, 10 and 15%) concentrations the parameters evaluated. Clavulanic acid was extracted into the PEG-rich phase (133.66 mg L−1), the highest values of the partition coefficient and yield being K = 5.92, Y = 103.53%, respectively The ATPS was not only effective on clavulanic acid extraction, but also its degradation was minimal. These results clearly indicate that ATPS can be successfully applied as a first step for the purification of clavulanic acid.