Determination of phenolic acids in plant extracts using CZE with on‐line transient isotachophoretic preconcentration

A novel transient ITP – CZE for preconcentration and determination of seven phenolic acids (caffeic acid, cinnamic acid, p ‐coumaric acid, ferulic acid, protocatechuic acid, syringic acid, and vanilic acid) was developed and validated. Effects of several factors such as control of EOF , p H and buffer concentration, addition of organic solvents and CD s, and conditions for sample injection were investigated. Sample self‐stacking was applied by means of induction of transient ITP , which was realized by adding sodium chloride into the sample. The CZE was realized in 200 mM borate buffer ( 9.2) containing 37.5% methanol, 0.001% hexadimethrine bromide, and 15 mM 2‐hydroxypropyl‐β‐ CD . Under the optimal conditions for analysis, analytes were separated within 20 min. Linearity was tested for each compound in the concentration range of 0.1–10 μg/mL ( R = 0.9906–0.9968) and the detection limits (S/N = 3) ranged from 11 ng/mL (protocatechuic acid) to 31 μg/mL (syringic acid). The validated method was applied to the ethanolic extract of E pilobium parviflorum , Onagraceae. The method of SPE was used for the precleaning of the sample.