## 2 Results and Discussion
### Optimization of Extraction Parameters
#### 2.1.3 Dispersive Solid-Phase Extraction with a 3D-Printed System  
Previously obtained results for LLE and SPE procedures were compared with those obtained using the DSPE technique, incorporating a new 3D-printed system. A commercially available Dow Styrene DVB sorbent was placed in the printed system. This sorbent can effectively extract a wide range of analytes from polar samples. By adjusting the sample pH, as well as the wash and elution solvents, DVB sorbents can be used for the analysis of acidic, basic, and neutral (both polar and non-polar) compounds. In this experiment, 30 mg of sorbent beads were weighed and placed in the extraction chamber of the 3D-printed system to facilitate the adsorption of analytes. The extraction process followed the procedure described in our previous publication, where it was tested for imipramine and carbamazepine quantification [41].  
In this paper, we present a new application of our previously described 3D-printed vessels for the isolation of DHPG, MHPG, and VMA from urine samples. We demonstrated that the dispersive extraction of DHPG, MHPG, and VMA with the aid of a Styrene-DVB sorbent is both effective and convenient. A schematic diagram of the 3D-DSPE-based extraction procedure is shown in Figure 1. Moreover, an evaluation of the extraction efficiency of the sorbent, potential for signal enhancement, and repeatability was conducted.  
The results obtained for both adsorbents used in this experiment (acetone and the ACN:MeOH mixture (50:50, _v/v_)) for samples at pH 5.8, turned out to be very promising. Satisfactory yields of the extraction process were obtained with the possibility of signal amplification. Acetone made it possible to achieve over 3-fold signal amplification for DHPG and MHPG and over 2-fold for VMA. Only slightly lower results were provided by the ACN:MeOH mixture (50:50, _v/v_) and were 2.9 times for DHPG, 2.4 times for MHPG, and 2.1 times for VMA, respectively (Table 5). More favorable results for the same type of sorbent and desorbent used in SPE procedure, may be attributed to a looser distribution of sorbent beads in the DSPE procedure, which increases the contact surface area with the sample matrix and the analytes contained within. In our 3D-DSPE procedure, both the extraction and desorption processes were enhanced by mechanically mixing the sample on a magnetic stirre  
Figure 1: Scheme of the general 3D-DSPE procedure for the extraction and desorption of the selected NE metabolites by Dow Styrene DVB sorbent from artificial urine samples.  
Generally, the DSPE technique is considered advantageous for sample preparation due to its simplicity and high recovery rates. DSPE is viewed as a variant of SPE, where a powdered sorbent is added directly to the liquid sample. Continuous stirring allows the analyte to adsorb onto the surface of the sorbent particles. The liquid phase is then separated from the solid sorbent, and an appropriate desorption solvent is added. One of the main challenges is the difficulty in effectively separating the powdered sorbent from the liquid extract. It is worth noting that DSPE has the significant advantage of requiring a much smaller amount of solvent. For this reason, novel solutions in dispersive extraction are still being explored to improve the separation of the sorbent from the sample matrix and achieve more efficient extraction results.