Off-line and On-line Enrichment of α-Aminocephalosporins for Their Analysis in Surface Water Samples Using CZE Coupled to LIF

This study examines the potential of application of capillary zone electrophoresis (CZE) coupled to laser-induced fluorescence (LIF) detection involving derivatization with fluorescamine for the separation and determination of α-aminocephalosporins in surface water samples. Via their α-amino group, the non-fluorescent cefadroxil and cefalexin are capable of forming a highly fluorescent derivative via their reaction with fluorescamine. This reaction permits the selective and sensitive detection of aliphatic primary amines when combined with CE/LIF, which was achieved with a low-noise diode laser emitting at a wavelength of 375 nm (P cw = 5.6 mW) in combination with a fiber optic-coupled detection cell. Different types of solid phase extraction cartridges were investigated to select the optimum solid phase providing maximum recovery for the studied antibiotics, which were extracted from spiked Lahn river water samples. Highest recovery (cefalexin 109.4 ± 3.9 % and cefadroxil 92.6 ± 4.0 %) was reached with a polymer-based solid phase (Oasis HLB cartridge), with which a tenfold off-line enrichment was obtained. On-line enrichment was achieved by sweeping and large volume sample stacking (LVSS). The high complex formation constant between the formed derivative and 2-hydroxypropyl-β-cyclodextrin (2-HP-β-CD) and the low electric conductivity of the extract after the off-line enrichment constitute an ideal basis for additional analyte enrichment by sweeping and LVSS. The enrichment efficiency obtainable with this on-line enrichment step (after having filled the complete capillary with the sample solution) in comparison to field-amplified sample stacking (FASS) reaches approximately an additional 25-fold improvement. With the developed method, combining off-line and on-line enrichment with optimized fluorescence detection, detection limits as low as 4.9 and 7.5 ng L⁻¹ are obtained for cefalexin and cefadroxil, respectively, with a starting sample volume as low as 50 mL. The high repeatability and accuracy of the proposed strategy permits its application to the analysis of α-aminocephalosporins in surface water samples. Its applicability can be extended to other environmental compartments and other types of primary amino group containing compounds. In addition, it provides equivalent sensitivity to other methods using more expensive equipment like HPLC–MS/MS.