This study established a highly effective and reliable method for the separation and quantitative
determination of five pharmacodynamic active components of I. sonchifolia using microemulsion
electrokinetic chromatography (MEEKC). The MEEKC conditions were investigated. The optimal
running buffer (pH 9.25) consisted of 80 mmol/L Brij-35, 0.8% (v/v) n-heptane, 8% (v/v) 1-
butanol, 25% (v/v) acetonitrile, 10 mmol/L sodium dihydrogen phosphate–10 mmol/L sodium borate
at 25 kV voltage. The regression equations showed good linear relationships, with 0.61–7.76 µg/mL
limit of detection and 2.04–25.85 µg/mL limit of quantitation. The established method was also accurate,
with intra-day and inter-day relative standard deviations less than 4.78% and less than 6.27%, respectively.
Recovery values ranged from 98.61% to 104.76%. The proposed method was successfully applied to determine
the five compounds in Kudiezi injection samples. A MEEKC method without adding neutral markers was further established
for dissociation constant (pKa*) measurement, and reliable pKa* values were obtained.