FIG 4.

Representative LC-MS/MS chromatograms for cefepime, meropenem, piperacillin, and tazobactam. (a) Total ion chromatogram (TIC) for human plasma with lithium heparin in a single sample spiked with the lowest calibration standards (LLOQ) for cefepime, meropenem, piperacillin, and tazobactam. (b) Typical chromatogram for human plasma with lithium heparin spiked with cefepime at the LLOQ (0.5 μg/ml). (c) Typical chromatogram for human plasma with lithium heparin spiked with meropenem at the LLOQ (0.1 μg/ml). (d) Typical chromatogram for human plasma with lithium heparin spiked with piperacillin at the LLOQ (0.1 μg/ml). (e) Typical chromatogram for human plasma with lithium heparin spiked with tazobactam at the LLOQ (0.25 μg/ml). (f) Typical chromatogram for human plasma with lithium heparin spiked with ²H₆-meropenem (2.5 μg/ml). (g) Typical chromatogram for human plasma with lithium heparin spiked with ²H₅-piperacillin (2.5 μg/ml).