## 2 Results and Discussion
### Determination of Pesticides in Agricultural Waters  
The developed and validated analytical method, using PDMS homemade needles for DI-SPME followed by the GC-MS method, was applied for the investigation of a series of surface and groundwater samples brought from different locations in the Qassim agricultural region (Saudi Arabia). Initially, a quick screening was applied to each sample using the optimized conditions, in order to identify those containing pesticide residues. In a second step, the samples identified as containing pesticide traces were analyzed again in three replicates in order to confirm and quantify the pesticides detected in the previous screening. Among the collected samples, five showed the presence of pesticides, while the remaining waters did not contain any detectable target pesticide. The results of these analyses are summarized in Table 2. Among the target pesticides, seven were identified and quantified in five examined agricultural and irrigation waters. The most contaminated  
\begin{table}
\begin{tabular}{l l c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Pesticide**} & \multirow{2}{*}{**Linear Equation**} & \multirow{2}{*}{**R\({}^{2}\)**} & \multirow{2}{*}{**Linear Range**} & \multirow{2}{*}{**LOD**} & \multirow{2}{*}{**LOQ**} & \multicolumn{3}{c}{**Precision RSD**} & \multicolumn{3}{c}{**Recovery \%**} \\  & & & & **Range (ng mL\({}^{-1}\))** & & & **(ng mL\({}^{-1}\))** & & **Intra-** & **–** & **–** & **–** & **–** & **–** \\  & & & & & & **Day** & **Day** & **mg** & **mg** & **mg** & **mg** & **–** & **–** \\ \hline
**Diazinon** & y = 1760\(\times\) - 17,390 & 0.9998 & 5-1000 & 2.1 & 6.3 & 0.8 & 16.5 & 102.55 & 19.5 & 104.90 & 12.5 \\ \hline
**Chloropyprophys-methyl** & y = 11,860\(\times\) - 102,442 & 0.9997 & 2.5-500 & 1.4 & 4.3 & 10.3 & 13.5 & 95.63 & 17.8 & 109.16 & 17.5 \\ \hline
**Priminphos-methyl** & y = 4958\(\times\) - 22,322 & 0.9993 & 2.5-250 & 2.3 & 6.9 & 7.4 & 9.5 & 114.03 & 4.0 & 95.35 & 8.0 \\ \hline
**Aldrin** & y = 3044.9\(\times\) + 83,228 & 0.9996 & 2.5-500 & 1.9 & 5.6 & 2.9 & 12.4 & 78.30 & 2.8 & 98.06 & 6.3 \\ \hline
**Malathion** & y = 773.6\(\times\) - 38,011 & 0.9997 & 2.5-500 & 2.1 & 6.2 & 3.1 & 3.9 & 103.94 & 15.7 & 93.49 & 8.1 \\ \hline
**Chloropyrifos** & y = 824.4\(\times\) + 196,208 & 0.9992 & 2.5-250 & 1.1 & 3.2 & 1.6 & 8.1 & 116.93 & 1.7 & 104.90 & 9.7 \\ \hline
**Profenofos** & y = 2906.8\(\times\) - 30,920 & 0.9990 & 1-500 & 0.8 & 2.3 & 7.6 & 15.2 & 82.22 & 14.4 & 95.34 & 4.4 \\ \hline
**Ehion** & y = 14,872\(\times\) - 30,223 & 0.9998 & 0.5-250 & 0.3 & 0.9 & 5.3 & 10.3 & 103.99 & 9.2 & 89.76 & 6.6 \\ \hline
**Tebuconazole** & y = 4404.9\(\times\) + 39,488 & 0.9999 & 1-500 & 0.7 & 2.0 & 11.3 & 16.0 & 98.06 & 8.4 & 90.54 & 8.4 \\ \hline
**Fenpropothrin** & y = 15,770\(\times\) - 215,106 & 0.9996 & 2.5-500 & 2.5 & 7.6 & 9.4 & 14.4 & 109.24 & 3.5 & 99.91 & 1.4 \\ \hline \(\lambda\)-Cylahothrin** & y = 4978.6\(\times\) - 110,934 & 0.9991 & 1-500 & 1.0 & 3.1 & 12.2 & 14.3 & 104.72 & 15.5 & 89.36 & 7.3 \\ \hline
**\(\lambda\)-Cylahothrin (iso)** & y = 6702.9\(\times\) - 125,201 & 0.9991 & 1-250 & 0.7 & 2.2 & 5.9 & 10.5 & 108.14 & 17.0 & 104.51 & 6.6 \\ \hline
**Deltamethrin** & y = 1641.1x - 7079.5 & 0.9993 & 2.5-500 & 2.5 & 7.5 & 10.7 & 13.6 & 77.56 & 13.2 & 116.23 & 4.9 \\ \hline \hline \end{tabular}  
* At a concentration of 100 ng mL\({}^{-1}\).  
\end{table}
Table 1: Main validation parameters obtained using the prepared in-needle SPME.  
waters were samples S1 and S6 with three and two pesticides, respectively, whereas only one pesticide was found in samples S2, S5, and S7.