Liquid chromatography on a monolithic column microfluidic chip coupled with "three-T" sample injection mode and amperometric detection

Abstract

An LC microfluidic chip (LC chip) with amperometric detection was developed. The LC chip employed a 7.5 cm long reversed-phase polymethacrylate monolithic column as a stationary phase and a "three-T" injection mode. A convenient interface was designed to conduct pump pressure into the microfluidic chip to drive solution, and a home-made device was used to control the distance between the working electrode and the LC chip accurately. The "three-T" sample injection mode completely avoided the problem of sample dilution and sample leakage during separation, which is usually observed in traditional and "T" type LC chip, without the using of valve and finally results in a better resolution, reproducibility and relatively high sensitivity. Using the proposed LC chip system, we have successfully separated two isomers, catechol and hydroquinone, within 12 min with a RSD (n=3) <3.0% for retention time and <2.4% for peak area. We have also successfully separated and determined 5-hydroxy-L-tryptophan, dopamine and 5-hydroxytryptamine within 25 min with a RSD (n=3) <5% (for peak area) and a detection limit of 0.16-0.51 μmol/L.