## 3 Results and Discussion
### Breakthrough Volume and Reusability  
The influence of the sample volume was investigated by loading different volumes of Milli-Q water (10, 20, 50, 100, 150 and 200 mL) fortified with CS and PMB at different concentrations, each one containing 10 \(\upmu\)g of the analytes on both MIP and NIP cartridges. From Figure S3A, it is demonstrated that target compounds can be retained well on MIP cartridge (recoveries higher than 89.7%) with a maximum loading volume of 100 mL. Losses of target analytes (recovery below 66.5%) were observed for sample volume of 150 mL. In contrast, when the NIP cartridge was used (Figure S3B), the losses of analytes were found for loading volumes as low as 20 mL, demonstrating again the existence of imprinted sites on MIP and its suitability for the analysis of CS and PMB in water samples. The reusability of MIP cartridge was evaluated by undergoing ten complete MISPE cycles (each cycle using 100 mL water spiked at 10 \(\upmu\)g of each analyte). Between cycles, the MIP cartridge was reconditioned by washing with 10 mL of water and 10 mL of MeOH. The results showed that the retention of studied analytes decreased slightly after ten cycles, although still with recoveries higher than 82.6%. This fact indicated a good stability and durability of synthesized MIP. Analytical Performance and Application of the Proposed MISPE Procedure to the Extraction of Polymyrins from Environmental Water Samples  
Under optimum conditions, linearity of the whole procedure was performed by plotting matrix-matched calibration curves at six concentration levels of 3, 5, 10, 20, 30 and 50 \(\upmu\)g/L in water samples. Good linearities were achieved in the experimental concentration range, with correlation coefficients (r) higher than 0.998. The limit of detection (LOD) and limit of quantification (LOQ), figured out through assaying the corresponding concentration at the points of signal-to-noise ratios of 3:1 and 10:1, are summarized in Table 1. LODs and LOQs were within the range of 1.0-2.0 \(\upmu\)g L\({}^{-1}\) and 3.0-6.5 \(\upmu\)g L\({}^{-1}\), respectively, depending upon the kind of sample and target analyte. The accuracy and precision of the proposed method, in terms of recovery and relative standard deviation (RSD), were measured by analyzing spiked water samples with both CS and PMB at 10 \(\upmu\)g L\({}^{-1}\) concentration level. Recoveries (also shown in Table 1) obtained for target analytes in river, lake and spring water were between 65.9% and 90.1%. Besides, the proposed method presents a satisfactory precision with intra-day and inter-day RSDs below 10.2% and 6.4%, respectively. Good recoveries and repeatability of this method could satisfy the fit-for-purpose criteria of the Commission Decision 2002/657/EC [34]. Figure 6 shows the chromatograms obtained from the blank and spiked (10 \(\upmu\)g L\({}^{-1}\)) river water samples after SPE on commercial C\({}_{18}\) and on proposed MIP cartridges. The C\({}_{18}\) cartridge was \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Water Source**} & \multirow{2}{*}{**Analyte 1**} & \multirow{2}{*}{**Intra-Day Recovery (RSD 2** **} & \multirow{2}{*}{**LOQ 3**  \\  & & **1** & **II** & **III** & **(RSD, \%, n = 9)** & (\(\upmu\)g L\({}^{-1}\)) & (\(\upmu\)g L\({}^{-1}\)) \\ \hline River & CSA & 74.7 (3.7) & 65.9 (4.5) & 75.7 (3.2) & 72.1 (7.3) & 2.0 & 6.5 \\  & CSB & 77.2 (3.6) & 72.1 (3.8) & 72.1 (1.9) & 73.8 (4.6) & 1.5 & 5.0 \\  & PMB & 83.7 (3.2) & 76.9 (9.7) & 83.6 (1.4) & 81.4 (6.3) & 1.0 & 3.0 \\ \hline Spring & CSA & 72.3 (2.1) & 71.6 (4.7) & 76.8 (1.2) & 73.6 (4.2) & 1.0 & 3.0 \\  & CSB & 74.6 (2.2) & 81.8 (3.9) & 74.4 (3.0) & 76.9 (5.5) & 1.0 & 3.0 \\  & PMB & 85.5 (5.3) & 83.1 (4.3) & 80.9 (10.2) & 83.2 (6.4) & 1.0 & 3.0 \\ \hline Lake & CSA & 83.1 (3.9) & 84.4 (6.2) & 86.4 (9.5) & 84.6 (6.3) & 2.0 & 6.0 \\  & CSB & 85.6 (3.7) & 86.7 (2.3) & 85.1 (3.6) & 85.8 (3.1) & 1.5 & 5.0 \\  & PMB & 83.8 (3.1) & 90.1 (1.8) & 84.5 (2.3) & 86.2 (4.0) & 1.0 & 3.0 \\ \hline \hline \end{tabular}
\end{table}