## 4 Sample Preparation
### Method Validation  
For method validation, linearity of the analytical curves, dynamic linear range, limit of detection (LOD), limit of quantification (LOQ), matrix effects (%), selectivity, precision (repeatability and intermediate precision), and trueness (expressed as % recovery) were assessed according to the guidance document on analytical quality control and method validation procedures for pesticides residues analysis in food and feed [11].  
Linearity and matrix effects were assessed, analyzing 2-chloroethanol analytical solutions at nine concentrations (0.008; 0.016; 0.02; 0.05; 0.10; 0.20; 0.50; 1.0; 2.0 mg/kg), corresponding to sum EtO, and a sample concentration of 0.011 mg/kg to 2.75 mg/kg (Figure 3). The dilution factors for this method were 2.5x its ratio sample weight/extract volume.  
Figure 2: Chemical conversion of ethylene oxide to 2-chloroethanol.  
Solutions were prepared in a pure organic solvent (acetonitrile) and in an extract of the blank matrix. An enrichment experiment with a solution of 2-chloroethanol and ethylene oxide was carried out. The samples were spiked at two concentrations, respectively 0.011 mg/kg and 0.11 mg/kg for dry samples (guar gum) and 0.044 mg/kg and 0.44 mg/kg for samples containing high water and oil content (sesame seeds) [Figure 3]. LOD is defined as the lowest repeatable fivefold detectable concentration level (RSD \(<\) 20%). The lowest LOD level for guar gum where the peak intensity was the lowest was estimated at 0.0022 for the full definition of ethylene oxide. The intensity of the peak at this level could be achieved by using the appropriate signal boost. For the remaining food matrices, an identical analytical approach was used to determine the LOD. However, the matrix effect increased the signal intensity for the remaining food matrices. Samples at the first and second enrichment level were repeated five times. The injection of the standard curve was repeated in duplicate, both with respect to the standard curve prepared in the solvent and the standard curve prepared in the appropriate matrix. The lowest concentration with recovery in the range of 70-120% and repeatability with an RSD of a maximum of 20% was defined. The accuracy (precision and reproducibility) of the method was calculated. The calculated validation parameters met the guidelines of the document SANTE/11312/2021 (Implemented by 1 January 2022) (Table 2).  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & & \multicolumn{4}{c}{**Guar Gum**} \\ \hline
**Spiking Level** & & & **Recovery \%** & & **Average** & \\ \hline
**mg/kg** & **Result 1** & **Result 2** & **Result 3** & **Result 4** & **Result 5** & **Recovery** & **RSDwR (\%)** \\ \hline
**0.011** & **103.6** & **102.4** & **101.0** & **100.0** & **100.2** & **101.4** & **1.5** \\ \hline
**Spiking Level** & & & **Recovery \%** & & & **Average** & \\
**mg/kg** & **Result 1** & **Result 2** & **Result 3** & **Result 4** & **Result 5** & **recovery** & **RSDwR (\%)** \\ \hline
**0.11** & **100.2** & **90.4** & **88.3** & **89.4** & **92.2** & **92.1** & **5.2** \\ \hline
**Spiking Level** & & & **Recovery \%** & & & **Average** & \\ \hline
**mg/kg** & **Result 1** & **Result 2** & **Result 3** & **Result 4** & **Result 5** & **recovery** & **RSDwR (\%)** \\ \hline
**0.0275** & **103.6** & **102.4** & **101.2** & **100.0** & **100.0** & **101.4** & **1.5** \\ \hline
**Spiking Level** & & & **Recovery \%** & & & **Average** & \\ \hline
**mg/kg** & **Result 1** & **Result 2** & **Result 3** & **Result 4** & **Result 5** & **recovery** & **RSDwR (\%)** \\ \hline
**0.275** & **100.2** & **90.2** & **88.3** & **89.4** & **92.4** & **92.1** & **5.2** \\ \hline \hline \end{tabular}
\end{table}
Table 2: Average recovery and RSDwR for specific matrices.  
Figure 3: Calibration curve of 2-chloroethanol in sesame seeds.