Sample injection is a crucial step in CE. In past, many efforts have been focused on concentrating the analytes into a sharp sample plug. In 2006, pressure-assisted electrokinetic injection (PAEKI) was proposed as a new preconcentration technique for anions. In this study, we expanded the applicability of PAEKI to online preconcentrate positively charged analytes. l-Arginine, l-lysine, and imidazole were chosen as target analytes for method development. The enhancement factor of PAEKI was over 3000-fold. When CZE was coupled with a Q-TOF system, PAEKI delivers a detection limit of 18-28 pg/mL and a dynamic calibration range over four orders of magnitude. The RSD was less than 6.4% (n = 4) on both peak area and migration time, indicating a good repeatability.