Fig 1.
(A) MS full-scan analysis showing the detection of ampicillin (m/z 350 Da) and its hydrolysis products ampicillin-penicilloic acid (m/z 368 Da) and penilloic acid (m/z 324 Da). Ampicillin and ampicillin-penicilloic acid were chosen for collision fragmentation into the specific products m/z 350→160 Da and m/z 368→324 Da. (B) Separations and quantifications were performed by LC-MS using an Agilent series 1100 LC system with an Zorbax Eclipse XDB-C18 column and a nonisocratic mobile phase that consisted of a continuous gradient of ammonium formiate and methanol at a temperature of 60°C and with an HCT Ultra mass spectrometer as detector. Specific masses with the specific CID products were eluted by 7.5 and 12 min. (C) MAAST linearity for the detection of ampicillin ranges from 0.1 to 100 μg/liter (coefficient of variation, <20%). (D) Kinetic analysis of bacterial ampicillin hydrolysis shows the decreasing amount of ampicillin and inverse gain of ampicillin-penicilloic acid. Ampicillin is completely degraded after 120 min. The drug/metabolite ratio allows a secure differentiation of ampicillin susceptibility and resistance after 30 min of incubation.