Multistep Plunger Injection Assisted Micellar-to-Solvent Stacking for the Determination of Alkaloids From Medicinal...

A simple, rapid, and efficient multistep plunger injection-assisted micellar to solvent stacking method was developed for the determination of cationic analytes from medicinal plants. In this method, a three-step sequential injection protocol was used, where sodium dodecyl sulfate (SDS), sample, and methanol (MeOH) solutions were introduced in succession to achieve an effective enrichment. The background solution contained 30 mM sodium dihydrogen phosphate and 30 mM citric acid. To achieve optimal enrichment efficiency, we systematically optimized several key parameters: surfactant type, SDS concentration, sodium dihydrogen phosphate concentration in the sample matrix, MeOH concentration, SDS injection time, MeOH injection time, and sample injection time. The optimal stacking conditions were as follows: injection of 10 mM SDS for 30 s, injection of the sample solution for 60 s, and injection of 40% MeOH for 10 s. This method exhibited an excellent linear relationship, as evidenced by the correlation coefficients (R²) ranging from 0.994 to 0.999. The intra-day and inter-day precision of this method was less than 3.701%, and the recovery rates of the analytes ranged from 92.70% to 107.79%, indicating satisfactory accuracy and reliability. Compared with conventional injection techniques, the sensitivity enrichment factors of the four analytes ranged from 42 to 44. The proposed method was validated for its applicability in detecting four alkaloids (fumarine, allocryptopine, tetrahydropalmatine, and corydaline) in Rhizoma corydalis samples.