Comparison of molecularly imprinted, mixed-mode and hydrophilic balance sorbents performance in the solid-phase extraction of amphetamine drugs from wastewater samples for liquid chromatography–tandem mass spectrometry determination

Recent studies have shown that amphetamines and other drugs of abuse residues occur in wastewater. Consequently, several methods have been developed for their determination by solid-phase extraction (SPE) and liquid chromatography–tandem mass spectrometry (LC–MS/MS). However, a major drawback of these methods is the lack of selectivity during SPE that results in reduced sensitivity, due to matrix effects, and in some cases in low precision and poor accuracy. In order to tackle this problem, three different SPE alternatives have been evaluated in this work for the determination of five amphetamines: common hydrophilic balance (Oasis HLB), mixed-mode (Oasis MCX) and molecularly imprinted polymers (MIPs) sorbents. Among them, Oasis HLB showed the worst performance, as three amphetamines (MDA, MDMA and MDEA) could not be determined because of interfering signals in the LC–MS/MS chromatogram, and amphetamine recoveries could not be corrected by the use of the deuterated analogue internal standard. Oasis MCX permitted the determination of all target analytes, but with still strong signal suppression: ca. 70% signal drop with wastewater samples, which could in this case be corrected by the internal standards providing acceptable trueness (overall recoveries: 101–137%), precision (RSD: 2.0–12%) and limits of detection (LOD: 1.5–4.4 ng/L). Alternatively, MIPs rendered cleaner extracts with less matrix effects (ca. 30% signal drop), and thus lower LODs (0.5–2.7 ng/L) and even better trueness (91–114% overall recovery) and precision (1.5–4.4%RSD). The final application of the method with MIP cartridges showed the presence of MDA and MDMA in the seven analysed wastewaters at the 4–20 ng/L level.