## 1 Introduction
For example, studies have reported using ethyl acetate or dichloromethane to extract, among others, MHPG, DHPG, and VMA from urine samples, achieving good recovery rates [28; 29; 30]. However, LLE may require large volumes of organic solvents and can be time-consuming. In a few studies, the sample preparation process before separation was based on the precipitation and elimination of proteins [25; 26; 30; 31]. Solid-phase extraction (SPE) is another popular method for isolating these analytes. SPE utilizes a sorbent to capture the analytes from the liquid phase. Different types of sorbents, such hydrophilic-lipophilic balanced (HLB) [1; 20; 32], mixed strong anion exchange absorbent (MAX) [33], octadecyl (C18) [27], or alumina [34], have been employed to optimize extraction efficiency. Studies indicate that SPE offers improved selectivity and lower solvent consumption compared to LLE. For instance, a study demonstrated that using C18 columns with methanol as the eluent effectively isolated DHPG, MHPG, and VMA from urine samples [27]. Solid-phase microextraction (SPME) involves the use of a coated fiber that adsorbs analytes from the sample matrix. It offers several advantages, including solvent-free extraction, simplicity,and rapid analysis. Studies have shown that SPME can effectively extract catecholamine metabolites, including MHPG, DHPG, and VMA, from biological matrices. For instance, some studies reported high recovery rates for these analytes using SPME coupled with gas chromatography-mass spectrometry (GC-MS), demonstrating its potential for sensitive detection of catecholamine metabolites [35]. Recent advancements have introduced dispersive solid-phase extraction (DSPE), which combines the advantages of SPE and LLE. DSPE involves adding a sorbent to the sample matrix and mixing, allowing the analytes to adsorb onto the sorbent particles. This method has been shown to enhance extraction efficiency and reduce solvent usage. In this study, we propose an alternative separation method using micellar-electrokinetic chromatography (MEKC), a high-resolution, environmentally friendly technique that enables rapid analysis while requiring minimal sample volume and solvents for the separation process. Since electromigration methods, such as MEKC, are generally less sensitive than HPLC techniques, it is essential to not only focus on the extraction efficiency of the analytes from the sample matrix but also on the potential for signal enhancement through the extraction process. Therefore, various approaches were tested in this study, which may prove promising and allow for the application of an optimal extraction method for the analysis of real samples. The primary aim of this work was to assess the effectiveness of extraction techniques, including liquid-liquid extraction (LLE), solid-phase extraction (SPE) with different modifications, and dispersive solid-phase extraction (DSPE) utilizing custom 3D-printed components. The extraction methods were evaluated and compared for the analytes DHPG, MHPG, and VMA. Notably, the application of the newly designed 3D-printed DSPE with commercially available DVB sorbent for isolating these analytes has not been previously reported in the literature.