# Contamination with Pharmaceuticals in Aquatic Environment: Focus on Analytical Methodologies
## 3 Determination of Pharmaceuticals in Environmental Samples
### Sample Preparation Techniques
#### 3.1.1 Solid-Phase Extraction (SPE)
For the extraction of surface water and drinking water samples, they used the SPE columns Strata-X (20 mm \(\times\) 2 mm, 25 \(\upmu\)m) for the analytes subsequently detected in positive ionization mode by the LC-MS/MS. A volume of 1 mL of surface water sample was satisfactory for analysis. The recoveries achieved by online SPE preparation (compared to direct injection of the sample, without preconcentration and with an injection volume of 20 \(\upmu\)L) for most monitored analytes were in the range of 90-120%, with the exception of the acetaminophen and trimethoprimm analytes, where they reached recoveries in the range of 70-80%. They verified and confirmed that the usability of the selected online SPE columns was up to 400 injections without changing the sensitivity, accuracy, or repeatability of the method. [PERSON] et al. [56] used online SPE for the preparation of surface water samples for the determination of 37 multi-residual xenobiotics (medicinal substances, pesticides, steroid hormones, UV filters, alkylphenols, and other contaminants). A volume of 2.5 mL of a portion of the sample (acidified with formic acid, pH = 1.6) and Oasis HLB SPE columns (20 \(\times\) 2.1 mm, 5 \(\upmu\)m) were used. Developing the method, the authors optimized the sample volume for online SPE, the SPE sorbent type, composition, and volume elution solvents, as well as the step of cleaning the sorbent after the elution of the analytes from the SPE column. By choosing online SPEs, they appear to significantly achieve low limits of determination at ultra-trace concentration levels (within the limit of quantification (LOQ) range from 0.1 ng/L to 10 ng/L). Other advantages of this are the eliminated sample handling, low solvent consumption, time aspect, and cost of analysis. The recoveries achieved by the online SPE preparation were in the range of 85-110% for all determined analytes. [PERSON] et al. [26] proposed an analytical method for the determination of 17 antibiotics in surface water samples. A combination of an online SPE system with LC-ESI-MS/MS was proposed. The target analytes were selected according to the recommendation of the Finnish Medicines Agency (FIMEA) and were the anticonvulsant carbamazepine and the antibiotics sulfadiazine, sulfamethoxazole, clarithromycin, oxytetracycline, tetracycline, trimethoprimm, and others. The online SPE columns used PLRP-S with the parameters 2.1 \(\times\) 12.5 mm and 15-20 \(\upmu\)m and a composition of macroporous polystyrene and divinylbenzene. [PERSON] et al. [26] tested the addition of different additives (formic acid, acetic acid, and ammonium formate) in the elution process after online SPE extraction. They found that a 0.1% addition of formic acid increased the sensitivity of the method in the positive ionization mode for the monitored analytes the most. They also tested the extraction volume of the sample and finally used a 1.8 mL portion of the surface water sample. The method showed satisfactory linearity (with determination coefficients of 0.989-0.999) in the tested range, and the achieved LOQ values were 1 to 50 ng/L. Alternative Sorption Materials  
In recent years, new extraction materials such as carbon nanotubes (CNTs), magnetic nanoparticles, magnetic cellulose nanoparticles, graphene, metal-organic frameworks (MOFs), restricted access material (RAM), and molecularly imprinted polymers (MIPs) have come to the forefront (Figure 2) [56]. Among the various SPE sorbents, MIPs are capable of selectively extracting one molecule or a group of analytes by utilizing their unique properties, such as functional groups, molecular shapes, and sizes. MIPs represent a specific type of sorbent that offers a highly selective retention mechanism to the extracted molecule of the target analyte or a group of structurally similar compounds [57]. This approach reduces the matrix effect and allows analysis using cost-effective analytical equipment such as liquid chromatography with a diode array detector.