## 3 Results and Discussion
### Method Validation  
The SPME-GC-ECD technique is an excellent and suitable analytical method to determine a large number of chlorinated pesticides in real water samples. The analytical parameters applied to validate the method were linearity, selectivity, accuracy, precision and detection limits. Calibration plots were used to determine various compounds in the water samples by plotting peak area versus compound concentrations. The linearity was observed at different concentrations using the least square regression method. The calibration plots of 20 organochlorine compounds at various concentrations (0.01 \(\upmu\)g L\({}^{-1}\) to 1 \(\upmu\)g L\({}^{-1}\)) provided good linear correlation, with \(R^{2}\) values in the range of 0.9887 to 0.9999. Lower limits of detection (LOD) (the lowest concentration of an analyte in a sample that can be detected by analytical instrument, however, not necessarily quantified under the stated conditions of the test) were obtained on the basis of a signal-to-noise ratio (S/N) of 3:1. To measure the signal-to-noise ratio of the instrument for various pesticides, very low concentrations (0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007 and 0.008 \(\upmu\)g L\({}^{-1}\)) of various pesticides were run on the GC. The \(R^{2}\) values, lower limits of detection and WHO guideline values are given in Table 2. The LOD for all 20 organochlorine pesticides were calculated in the range of 0.002-0.03 \(\upmu\)g L\({}^{-1}\), and were found to be lower than their maximum permissible contamination levels. Various researchers have determined that the LOD for different organochlorine pesticides ranges from 0.001-0.025 \(\upmu\)g L\({}^{-1}\)[43], 0.008-0.020 \(\upmu\)g L\({}^{-1}\)[19], and 0.039-0.340 \(\upmu\)g L\({}^{-1}\) (EPA 525.2 method) [44]. \begin{table}
\begin{tabular}{c c c c c c c} \hline \multirow{2}{*}{**Compound**} & \multirow{2}{*}{**Correlation**} & \multicolumn{4}{c}{**Lower Limits of Detection (ug L\({}^{-1}\))**} & \multirow{2}{*}{**Guide Line**} \\  & & & & **[PERSON] et al.**, & **2009** & **Golfinopoulos** \\  & & & & **EPA 525.2 1 **} \\  & & & **2003** & 0.008 & 0.110 & - \\ \(\upmu\)-BHC & 0.9996 & 0.006 & 0.005 & 0.020 & 0.085 & - \\ \(\upmu\)-BHC & 0.9998 & 0.002 & 0.008 & 0.008 & 0.084 & 2 \({}^{\circ}\), 0.05 \({}^{\text{d}}\), 0.2 \({}^{\text{e}}\) \\ \(\upmu\)-BHC & 0.9995 & 0.003 & 0.006 & 0.008 & 0.049 & 0.05 \({}^{\text{d}}\) \\ Heptachlor & 0.9997 & 0.004 & 0.007 & 0.008 & 0.061 & 0.03 \({}^{\circ}\), 0.4 \({}^{\circ}\), 0.05 \({}^{\text{d}}\) \\ Aldrin & 0.9998 & 0.002 & 0.009 & 0.008 & 0.045 & 0.03 \({}^{\circ}\), 0.01 \({}^{\text{d}}\) \\ Heptachlor & 0.9887 & 0.02 & 0.002 & 0.008 & 0.130 & 0.03 \({}^{\circ}\), 0.2 \({}^{\text{e}}\) \\ \(\upmu\)-Chordane & 0.9996 & 0.003 & - & 0.008 & - & 0.2 \({}^{\circ}\), 2 \({}^{\circ}\), 0.01 \({}^{\text{d}}\) \\ \(\upmu\)-Chordane & 0.9995 & 0.002 & - & 0.008 & - & 0.2 \({}^{\circ}\), 2 \({}^{\circ}\), 0.2 \({}^{\text{e}}\) \\ Endosulfan & 0.9998 & 0.002 & 0.005 & 0.008 & 0.110 & 0.05 \({}^{\text{d}}\) \\ \(4\), \({}^{\text{d}}\)-DDE & 0.9997 & 0.004 & 0.002 & 0.008 & 0.070 & 0.06 \({}^{\text{d}}\) \\ Dieldrin & 0.9998 & 0.002 & 0.004 & 0.008 & 0.150 & 0.03 \({}^{\circ}\), 0.01 \({}^{\text{d}}\) \\ Endwin & 0.9947 & 0.004 & 0.004 & 0.008 & 0.340 & 2 \({}^{\text{e}}\) \\ Endosulfan II & 0.9998 & 0.003 & 0.025 & 0.008 & 0.074 & 0.05 \({}^{\text{d}}\) \\ \(4\), \({}^{\text{d}}\)-DDD & 0.9957 & 0.005 & 0.004 & 0.008 & 0.055 & \\ Endrin aldehyde & 0.9976 & 0.004 & 0.001 & 0.008 & 0.150 & \\ Endrin ketone & 0.9968 & 0.003 & 0.004 & 0.008 & - & \\ \(4\), \({}^{\text{d}}\)-DDT & 0.9955 & 0.009 & 0.004 & 0.020 & 0.093 & 2 \({}^{\text{e}}\), 0.06 \({}^{\text{d}}\) \\ Endosulfan & 0.9999 & 0.002 & 0.003 & 0.008 & 0.039 & 0.05 \({}^{\text{d}}\) \\ Multenoychlor & 0.9899 & 0.03 & 0.001 & 0.008 & 0.130 & 20 \({}^{\text{e}}\), 0.2 \({}^{\text{d}}\) \\ \hline \end{tabular}
\end{table} 
Table 2: The Linear range, \(R^{2}\) values, lower limits of detection and WHO guideline values for selected pesticides.