Field-Amplified Sample Injection and Solid-Phase Extraction for Sensitivity Improvement of Electrophoretic Determination of Indole-3-Acetic Acid and Indole-3-Butyric Acid in Food Samples

A sensitive method has been established by using activated carbon as an adsorbent for extraction of indole-3-acetic acid (IAA) and indole-3-butyric acid (IBA) from bean sprout, tomato, potato, cucumber, and wheat grain prior to field-amplified sample injection-micellar electrokinetic capillary chromatography (FASI-MEKC) detection. Parameters affecting FASI and solid-phase extraction (SPE) were optimized in detail. Under the optimal conditions, the sensitivity of SPE-FASI-MEKC for IAA and IBA was respectively improved by 32.5 and 29.7 times as compared with the direct MEKC. The detection limits were 4.1 for IAA and 5.3 ng mL −1 for IBA with 4.9–5.2% RSD ( n  = 9, C  = 0.03 μg mL −1 ). The new method has been successfully applied to detect IAA and IBA in bean sprout, tomato, potato, cucumber, and wheat grain with the recoveries of 81.7–110%.