Determination of beta-lactam antibiotics in milk using micro-flow chemiluminescence system with on-line solid phase extraction.

In this paper, a chemiluminescence (CL) micro-flow system combined with on-line solid phase extraction (SPE) is presented for determination of beta-lactam antibiotics (penicillin, cefradine, cefadroxil, cefalexin) in milk. It is based on the enhancement effect of beta-lactam antibiotics on the luminol-K3Fe(CN)6 CL system. The micro-flow system was fabricated from two polymethyl methacrylate (PMMA) plates (50 mm x 40 mm x 5 mm) with the microchannels of 200 microm wide and 150 microm deep. C18-modified silica gel was packed into the microchannel (length: 10 mm; width: 1 mm; depth: 500 microm) to serve as SPE device. Extraction and preconcentration of the analytes were carried out using on-line SPE micro-flow system and the selectivity of CL detection was improved. The detection limits were 0.5 microg mL(-1) of penicillin, 0.04 microg mL(-1) of cefradine, 0.08 microg mL(-1) of cefadroxil and 0.1 microg mL(-1) of cefalexin. The proposed method was also applied to analyze the beta-lactam antibiotics in milk. Experimental results were in good agreement with those obtained by high performance liquid chromatography (HPLC) method with UV detection.