## 3 Results and Discussion
### Analytical Performance and Application of the HFM-Protected-MI-MSPE of Triazines in Soil Samples  
The developed HFM-protected-MI-MSPE procedure was then applied for the determination of triazines in soil samples. In order to demonstrate the feasibility of the proposed method, soil samples of different Spanish locations were selected. Spiked (10 ng g\({}^{-1}\) of each triazine) and non-spiked crude soil extracts were prepared as described above and analysed with and without performing selective HFM-protected-MI-MSPE. Figure 3 shows a comparison of the results obtained for the analysis of the agricultural soil samples from the Murcia region. Figure 3a,b shows the HPLC-UV analysis of a spiked soil sample extract without and with performing the selective HFM-protected-MI-MSPE, respectively. As can be seen, direct analysis of spiked crude soil extract provides a chromatogram with a big hump of organic matter and a highly noisy baseline with a lot of interfering peaks. Consequently, identification of the selected triazines by means of the UV spectrum comparison tool provided by the diode-array software was only possible for cyanacine (peak number 2), since the match factors obtained for the peaks appearing at the retention times of the other triazines were lower than 950. In contrast, by using the proposed HFM-protected-MI-MSPE procedure (Figure 3b), detection and quantification of all triazines could easily be accomplished, thanks to the high selectivity of the MIP microspheres. The high degree of clean-up achieved resulted in a chromatogram almost free of matrix interference, in which match factors obtained by spectral comparison were higher than 980 for all the selected triazines. Finally, analysis of non-spiked samples by HFM-protected-MI-MSPE permits the conclusion that triazines were not present in that soil (Figure 3c). Figure 2: Mean recoveries (%R for \(n=3\)) obtained for the optimization of the retention of the different triazines in the MIP fibre. Another illustrative example of the selectivity provided by the developed method can be seen in Figure 4. In this case, the chromatograms correspond to the analysis of soil samples collected in L'Albufera (Valencia, Spain). Spiked soil sample extracts (10 ng g\({}^{-1}\)) analysed directly or after HFM-protected-MI-MSPE are shown in Figure 4a,b, respectively; Figure 4c corresponds to the analysis of a non-spiked sample under the proposed procedure. The obtained results were very similar, with the identification of atrazine, propazine and terbutylazine in the crude sample extract being, in this case, impossible; whereas the match factors obtained following the proposed procedure (Figure 4b) surpassed 975 for all the triazines selected in this work. Finally, non-agricultural soil samples collected in Madrid were also analysed, and the results were as satisfactory as those obtained for both agricultural soils described above. Figure 3: Comparison of chromatograms obtained in the analysis of soil samples from Murcia: (**a**) Spiked crude soil sample extract (10 ng g\({}^{-1}\)); (**b**) Spiked soil sample extract (10 ng g\({}^{-1}\)) after performing HFM-protected-MI-MSPE; (**c**) non-spiked soil sample extract after performing HFM-protected-MI-MSPE. Peak assignment: 1. SIM; 2. CYA; 3. ATZ; 4. PPZ; 5. TER. Table 1 summarizes all the obtained results and the analytical performance of the proposed method in the different soil samples. For the recovery and precision study, three different samples of each soil were enriched with 10 ng g\({}^{-1}\) of each triazine and analysed by the proposed procedure. Mean recovery values varied between 72% and 103%, with RSDs lower than 11% proving the high accuracy and repeatability of this method.