UHPLC with electrochemical detection for the quantitative determination of monoamines in microdialysis samples

To determine the monoamines dopamine (DA), noradrenaline (NAD) and serotonin (5-HT) in microdialysis samples, ion-pair liquid chromatography (LC) with electrochemical detection (ECD) is typically applied. Because of the low concentrations in the extracellular space (pM range), further dilution in the microdialysis samples, the complexity of the samples and the required temporal resolution, the analysis is challenging [1]. In addition, sensitivity should be further increased to allow detection of these monoamines in small brain areas and in smaller animals or to increase the validity in situations where monoamine levels are decreased. Furthermore, there is an increasing demand in the development of high-throughput analysis. In recent years, ultra-high performance LC (UHPLC) has been introduced as a way to increase the efficiency and speed of analysis by use of columns packed with sub-2 μm particles [2]. An optimal UHPLC-ECD method would be one with a short analysis time, a high sensitivity for the three monoamines and a good separation of NAD, which is the most hydrophilic compound, towards the front peak. The coupling of UHPLC with ECD for the analysis of low concentrated samples has not been explored till now.