## 2 Materials and Methods  
### Standards and Materials  
The SCs standards of \(\alpha\)-PVP and MDPBP were previously synthetized with a purity of higher than 98% [27; 28], while methylene, MDPV, MDPPP, and \(\alpha\)-PVT were provided by the Forensic Sciences Laboratory from the Portuguese Judiciary Police (Lisbon, Portugal). Pure samples of methylene, MDPV, MDPPP, and \(\alpha\)-PVT were characterized through nuclear magnetic resonance (NMR). A small sample of each cathinone (10 to 15 mg) was dissolved in DMSO-\(d_{6}\) in order to accomplish the NMR structural analysis (Bruker Advance spectrometer, Bremen, Germany) through \({}^{1}\)H NMR (400.1 MHz) and \({}^{13}\)C NMR (100.6 MHz). The chemical shifts were expressed as \(\delta\) values and referenced to the residual solvent peak (DMSO-\(d_{6}\), \(\delta_{\rm H}=2.50\), and \(\delta_{\rm C}=39.5\)) using Hertz (Hz) as the reporting unit for the coupling constants. One-dimensional (\({}^{1}\)H and 13C APT) and 2D (COSY, HMBC, and HSQC) NMR experiments were used to achieve the assignments of all \({}^{1}\)H and \({}^{13}\)signals. The NMR data obtained for methylene and MDPV in DMSO were similar to previously reported data [29; 30]. For MDPPP and \(\alpha\)-PVT, the NMR data were consistent with the literature data in different NMR solvents [31; 32; 33]. The full \({}^{1}\)H and \({}^{13}\)C NMR assignments for these last two SCs in DMSO are reported here for the first time. The purity of all the SCs (\(\geq\)98%) was confirmed by GC-FID analysis using an Agilent GC system 7890B series with a flame ionization detector and Agilent 19091J-413 HP-5 capillary column (30 m \(\times\) 320 \(\upmu\)m \(\times\) 0.25 \(\upmu\)m). Samples were dissolved in methanol/chloroform (1/1, \(v/v\)) and 1 \(\upmu\)L of the solution was injected in split mode 40:1. The GC oven was programmed at 80 \({}^{\circ}\)C (1 min) and heated at a rate of 12 \({}^{\circ}\)C/min to 270 \({}^{\circ}\)C (7 min). The NMR data can be found in the Supplementary Materials.  
The employed solvents and materials were similar to previously published works [21; 23], including HPLC-grade methanol (MeOH) and acetonitrile (ACN), as well as NaCl, NaOH, and HCl supplied by Carlo Erba (Arese, Italy), AnalaR BDH Chemicals (Lutterworth, UK), Riedel-de Haen (Seelze, Germany), Scharlau (Barcelona, Spain), and Panreac (Barcelona, Spain). The ultra-pure water was from Milli-Q water purification systems from Merck Millipore (Jaffrey, NH, USA). The commercial-activated carbon materials were SX1, N2, and R, supplied by Norit (Amersfoort, Netherlands) and supplied by both Salmon & Cia. (Lisbon, Portugal) and Riedel-de Haen (Seelze, Germany). The polymeric phases tested were based on \(N\)-vinylpyrrolidone (Strata-X), styrene-divinylbenzene (PS-DVB) (Strata-DVB), divinylbenzene (DVB), and pyrrolidone copolymer of weak cationic exchange (WCX) and ethylvinylbenzene polymer (LiChrobut EN), and were supplied by Phenomenex (Torrance, CA, USA) and Sigma-Aldrich (St. Louis, MI, USA). All polymers presented a pH stability between 1 and 14. The characteristics of the activated carbons and polymeric phases, such as the point of zero charge (pH\({}_{\text{PZC}}\)) and surface area, as well as the particle and pore sizes, can already be consulted in the literature [21; 23]. Stock solutions of individual analytes (1000.0 mg L\({}^{-1}\)) were prepared in MeOH, stored at \(-20\)\({}^{\circ}\)C, and renewed every month. Working standard mixtures of 10.0 \(\upmu\)g L\({}^{-1}\) were prepared daily using a MeOH/ACN (1/1, \(v/v\)) solution and used for sample spiking. For instrumental calibration, standard mixtures were prepared in MeOH by appropriate dilution from previous stock solutions.