Large volume sample stacking of cationic tetracycline antibiotics toward 10 ppb level analysis by capillary...

This paper aimed to build up a sensitive CE method for the analysis of tetracyclines (TCs) antibiotics (including tetracycline, chlorotetracycline, oxytetracycline, and doxycycline) with conventional UV detection. Here, the large volume sample stacking was applied to achieve in capillary preconcentration of the targets. To achieve large volume sample stacking, the essential step was a large volume of sample (around 83.3% of total capillary length from inlet to detection window) hydrodynamically loaded. Then, the reserved voltage was added in order to push the sample matrix out of the capillary. Due to different pH between sample solution (pH 4.6) and BGE (pH 11.0), the cationic TCs would turn into negatively charged while the sample matrix was removing from the capillary. Finally, the anionic TCs were stacked at the inlet for the subsequent separation. Although the loss of sample existed during their charge transformation, the LODs could be improved around 40 times than that obtained by normal hydrodynamic injection CE method. Here, the LODs were in the range of 8.1-14.5 μg/L, around 10 ppb that close to the level by electrochemiluminescence or laser-induced fluorescence detection of TCs by CE. The precision was characterized by RSDs of migration times and peak areas, which were in the range of 0.19-0.24% and 0.97-2.54%, respectively. The recoveries of the developed method were in the range of 95-112% by spiking TCs in the tap water. The proposed inline preconcentration CE method could be a simple, speed, and sensitive method for the quantitative analysis of TCs.