## 3 Results and Discussion
### Validation Parameters  
Table 2 presents some analytical figures of merit obtained in this study. The linear coefficient of determination (R2) values were >0.95, which indicates a good linear fit. The LOD and LOQ values were satisfactory based on those obtained in other studies.  
Precision was evaluated in terms of intra-day repeatability (\(n=3\)) and inter-day reproducibility (\(n=9\)) using samples spiked at the lowest level for each analyte. The results obtained are shown in Table 3. It can be observed that the intra-day and inter-day precision for diatomaceous earth fiber presented values of RSD <15% and <17%, respectively. Relative recovery showed results between 83% and 100%, confirming the accuracy of the method.  
The selectivity of the proposed method was confirmed by the absence of peaks in the retention time of the target analytes when chromatograms of the extract were obtained from the river water sample without the addition of the analytes. The only exceptions were pyrene, chrysene, and benzo[a]pyrene, but these peaks were not quantifiable. Figure 5 shows the chromatograms obtained for samples of spiked river water (10 ug L\({}^{-1}\)) and non-spiked river water.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Analyte** & \begin{tabular}{c} **LOD** \\ **(ug L\({}^{-1}\))** \\ \end{tabular} & \begin{tabular}{c} **LOQ** \\ **(ug L\({}^{-1}\))** \\ \end{tabular} & \
\begin{tabular}{c} **Linear Range** \\ **(ug L\({}^{-1}\))** \\ \end{tabular} &
\begin{tabular}{c} **Linear Equation** \\ **Linear Equation** \\ \end{tabular} & **R** \\ \hline Acenaphtylene & 0.16 & 0.49 & 0.49–25 & y = 66,956\(\chi\) - 30,445 & 0.9890 \\ Fluorene & 0.17 & 0.50 & 0.50–25 & y = 87,809\(\chi\) - 54,517 & 0.9911 \\ Phenanthrene & 0.14 & 0.42 & 0.42–25 & y = 326,563\(\chi\) - 245,240 & 0.9777 \\ Anthracene & 0.11 & 0.33 & 0.33–25 & y = 364,057\(\chi\) - 339,574 & 0.9598 \\ Pyrene & 0.15 & 0.50 & 0.50–25 & y = 979,497\(\chi\) - 935,649 & 0.9914 \\ benzo[a]anthracene & 0.03 & 0.10 & 0.10–25 & y = 506,040\(\chi\) - 544,597 & 0.9832 \\ Chrysene & 0.14 & 0.42 & 0.42–25 & y = 691,902\(\chi\) - 796,526 & 0.9592 \\ benzo[b]fluoranthene & 0.06 & 0.17 & 0.17–25 & y = 158,587\(\chi\) - 50,481 & 0.9990 \\ benzo[k]fluoranthene & 0.11 & 0.33 & 0.33–25 & y = 431,634\(\chi\) - 806,517 & 0.9848 \\ benzo[a]pyrene & 0.15 & 0.46 & 0.46–25 & y = 295,450\(\chi\) - 567,387 & 0.9667 \\ \hline \hline \end{tabular}
\end{table}
Table 2: The linear range, linear equation, linearity, and limits of detection and quantification for the method developed using diatomaceous earth coating.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Analyte** & \begin{tabular}{c} **Spiked Concentration** \\ **(ug L\({}^{-1}\))** \\ \end{tabular} & \begin{tabular}{c} **Relative Recovery (\%)** \\ **(\(n=3\))** \\ \end{tabular} & \begin{tabular}{c} **RSD,** \\ **Intra-Day (\%)** \\ **(\(n=3\))** \\ \end{tabular} & \
\begin{tabular}{c} **RSD,** \\ **Intra-Day (\%)** \\ **(\(n=3\))** \\ \end{tabular} &
\begin{tabular}{c} **RSD,** \\ **Inter-Day (\%)** \\ **(\(n=3\))** \\ \end{tabular} \\ \hline acenaphtylene & 0.5 & 100 & 5 & 10 \\ fluorene & 0.5 & 83 & 15 & 10 \\ phenanthrene & 0.5 & 97 & 10 & 13 \\ anthracene & 0.5 & 93 & 13 & 3 \\ pyrene & 0.5 & 92 & 2 & 6 \\ benzo[a]anthracene & 0.5 & 94 & 2 & 6 \\ chrysene & 0.5 & 96 & 2 & 6 \\ benzo[b]fluoranthene & 0.5 & 90 & 15 & 17 \\ benzo[k]fluoranthene & 0.5 & 97 & 15 & 17 \\ benzo[a]pyrene & 0.5 & 93 & 7 & 17 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Relative recovery of analytes and precision (inter- and intra-day) for the extraction of PAHs from spiked river water samples.