## 4 Methods Validation
Few documents show the LOD and LOQ based on the standard deviation of the method (Sm), LOD = 3 \(\times\) Sm and LOQ = 10 \(\times\) Sm, respectively. Sm is the ratio between the relative standard deviation of the standard addition calibration curves (Sy/x) and its slope (b) [23; 60]. The confirmation of the LOQ with a standard control with the same concentration value for the target compound was not performed for most of the studies. Besides, when used, it has a concentration higher than the LOQ. Most of the studies evaluated the precision under repeatability and reproducibility conditions. The instrumental trueness is also assessed, but the trueness of the global method,pre-treatment and chromatographic method, is not always considered with certified reference materials (CRM) or spiked samples with appropriate concentration ranges [27]. Matrix effects, extraction efficiency, and absolute recovery of the developed analytical methods should always be determined [109; 175; 178]. Usually, the matrix effect is evaluated by recovery studies. However, the spiked concentrations are sometimes too high when compared to concentration values that were obtained in real samples. Some authors reported recoveries around 100% determined with surrogates. However, these values should have been reported as relative recoveries. This approach did not well evaluate the extraction efficiency. Although the recoveries higher than 70% are desirable, lower recoveries, even those lower 40% have been acceptable when their repeatability was good, to obtain as much information as possible regarding the presence of PhACs in environmental waters. When the ones corrected the SPE recoveries with the corresponding surrogates, the percentage of compounds with relative recovery around 100% increased significantly [44; 64; 221]. Notwithstanding the uncertainty estimate should be a necessary component of an analytical result, it is still a severe problem, especially in monitoring the presence of pharmaceuticals in the environmental waters [87]. There are several possible approaches to determine the uncertainty [237]: (i) bottom-up; (ii) fitness-for-purpose; (iii) top-down; (iv) validation-based; and, (v) robustness-based-based on robustness tests from interlaboratory studies. However, there are few papers relative to the estimation of expanded uncertainty of the methods for determining PhACs in environmental water samples. [PERSON] et al. [150] reported expanded uncertainties between 8.5% to 29.0% for NSAIDs and antiepileptic drugs in river water by SPE- LC-DAD. [PERSON] et al. [59] compared the expanded uncertainties that were obtained by bottom-up approach (method 1) and the top-bottom approach (method 2) in the quantification of endocrine disrupters in natural and drinking waters by SPE-LC-MS/MS [238; 239]. The estimation of uncertainty by method 1 was between 18% and 26%, while, by method 2, it was between 15% and 30%. In method 1, the calibration component of uncertainty had the highest contribution to the expanded uncertainty. In method 2, there were no statistically significant differences between the contribution of the variability component and the accuracy component to the expanded uncertainty (\(p\) value = 0.60). [PERSON] et al. [217] compared the expanded uncertainties of on-line and off-line SPE coupled to LC-DAD-MS technique to determine NSAIDs. The uncertainties ranged from 15% to 37% with on-line SPE and 19% to 64%with off-line SPE. [PERSON] et al. [87] showed a procedure to facilitate the introduction of uncertainty estimation in chromatographic measurements to the analysis of pharmaceutical residues in environmental sample waters. The proposed method is in line with the Guide to the Expression of Uncertainty in Measurement (GUM) [239]. The uncertainties ranged from 4.2% to 69.7% for eleven antibiotics in marine waters by SPE disks-LC-MS/MS.