In-Syringe Binary-Solvent Liquid-Phase Microextraction for the Preconcentration of Cinnamic Acid Derivatives in Traditional Chinese Medicine Samples

Abstract

An in-syringe binary-solvent liquid-phase microextraction (in-syringe BSLPME) coupled to high-performance liquid chromatography with diode-array detection (HPLC/DAD) has been established and applied for the determination of four cinnamic acid derivatives (caffeic acid, p-hydroxycinnamic acid, ferulic acid, and cinnamic acid) in traditional Chinese medicine samples. In this method, 70 µL of n-pentanol/n-hexanol (5:5, v:v) mixture as extractant were added to the surface of a solution containing target analytes in a disposable syringe and the solution was manually shaken for a desired time. After the re-aggregation of binary-solvent droplets, the extraction phase was impelled out of the syringe for HPLC analysis. The variables influencing in-syringe BSLPME, such as extraction solvents (types, volume ratios, and volumes), extraction time, sample phase pH, ionic strength, sample volume, and disperser solvent, were investigated. Under the optimized conditions, the limits of detection were between 0.2 and 1.3 ng mL−1 with enrichment factors from 28 to 58. The calibration graphs were linear in the range of 1.0 × 10−2–7.0 µg mL−1 for caffeic acid, 1.3 × 10−3–1.9 µg mL−1 for p-hydroxycinnamic acid, 2.8 × 10−3–4.1 µg mL−1 for ferulic acid, and 2.7 × 10−3–4.1 µg mL−1 for cinnamic acid, with r 2 better than 0.9912. The precision expressed as relative standard deviation varied between 1.4 and 9.6%. In-syringe BSLPME was verified reliable for the determination of cinnamic acid derivatives in Chinese herbal medicines with recovery values from 94.2 to 106.7%. The proposed method was compared with other dispersive liquid-phase microextraction methods. Results showed that the developed method was easy-to-handle, efficient, and rapid for the analysis of active constituents in Chinese medicine samples.