A highly selective molecularly imprinted solid phase extraction (MISPE)-pulsed elution (PE) method coupled with electrospray mass spectrometry (MS) was developed for the rapid screening and determination of cephalexin in α-aminocephalosporin antibiotics. This method involved the solid phase extraction of cephalexin using a molecularly imprinted polymer micro-column, and pulsed elution with 1% trifluoroacetic acid in methanol, which contains sulindac as an internal standard for enhanced precision in MS detection. An LC/MS spectrometer was operated in the positive electrospray mode, and the selected-ion-recording (SIR) function was employed to detect the molecular ions of cephalexin, cefradine, cefadroxil and sulindac at m/z 348, 350, 363 and 357. Linearity was achieved in the cephalexin concentration range from 0.3 to 25 μg/ml (or 5-500 ng) (R 2 = 0.998). The detection limit was estimated at 0.04 μg/ml (or 0.8 ng) of cephalexin. Advantages of the newly developed MISPE-PE-MS, over the previously reported MISPE-DPE-FPE-UV, were evidenced in terms of detection limit, analysis time, solvent consumption, and simplicity of method development.

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Journal of Pharmaceutical and Biomedical Analysis
Department of Chemistry

Wu, S.G. (Stanley G.), Lai, E.P.C, & Mayer, P.M. (Paul M.). (2004). Molecularly imprinted solid phase extraction-pulsed elution-mass spectrometry for determination of cephalexin and α-aminocephalosporin antibiotics in human serum. Journal of Pharmaceutical and Biomedical Analysis, 36(3), 483–490. doi:10.1016/j.jpba.2003.05.001