Fresh nitrocefin buffered solution at a concentration of 2 mM and volume of 1 mL was injected into the filter column. After 6h, the nitrocefin elution was collected and a sample of 50 µL was placed in clear UV-Star 96-well plates (Greiner flat-bottom). The plate was transformed to Biotek Synergy H1 plate reader (Biotek, Winooski, VT, USA) and the absorbance was recorded at λ= 380 nm, detecting the non-reacted nitrocefin. A similar analysis was performed using penicillin and amoxicillin, dissolved in DIW at a concentration of 60 µM. 100 µL of each antibiotic-solution was added to the column and elution solutions were collected in 5 µL drops, in time intervals of 0, samples they were mixed with 95 µL organic solvent to quench the spontaneous hydrolysis reactions (acetonitrile for amoxicillin, methanol in the case of penicillin). The samples were injected sequentially into the LC-MS analysis as described above.