**4. Results and discussion**

### **4.1 Method validation**

All the 35 certified reference materials of pesticides were determined in a single chromatographic window of 22 min run time (**Figure 1**). For most of the compounds, the R<sup>2</sup> values (correlation coefficients) of the calibration curve were >0.99 for both pure solvent-based and matrix-matched samples. The recovery of all of the compounds was found to be 70–100% with RSD below 14%. **Figure 2** shows chromatograms of typical pesticide peak shapes. The grape sample extracts were slightly yellow because of the co-extraction of carotenoids in the ethyl acetate. It was found that a two-step homogenization procedure significantly increased the precision of analysis. It was also observed that the use of high-speed homogenization process

**103**

as follows:

phthalimides such as captan.

**Figure 2.**

**4.2 Recovery experiments of spiked samples**

*Chromatograms showing DEET and phenthoate peak shapes.*

*Gas Chromatographic-Mass Spectrometric Detection of Pesticide Residues in Grapes*

for precooled sample did not necessarily increase the temperature of the system above 10°C and thereby proved very useful for maintaining the stability of the

Usually, the extraction and cleanup procedure removes the matrix co-extractives then separates all of the analytes from the matrix. The same does not holds good in most of the matrices during the pesticide residue analysis. As a result, the actual recovery experiments were performed on grape samples. The separated peaks with their tM (retention times) are summarized in **Table 1**. Using the linear regression equation recoveries of individual pesticides with different levels of spiking along with replicates were calculated in grape matrix. **Table 1** gives the average recoveries for all spiked pesticide standards at each spiked level in grape samples. All the tested 35 pesticides displayed a recovery range between 70 and 100% which is quite acceptable. RSD (relative standard deviation) was used to express the reproducibility, and most of the RSD values were found to be less than 14%. Recovery study is conducted using a control sample and at least two fortification levels with three replications. The formula for arriving percentage recovery for method validation is

*DOI: http://dx.doi.org/10.5772/intechopen.80438*

**Figure 1.** *Total ion chromatogram of 35 certified reference standards.*

*Gas Chromatographic-Mass Spectrometric Detection of Pesticide Residues in Grapes DOI: http://dx.doi.org/10.5772/intechopen.80438*

**Figure 2.** *Chromatograms showing DEET and phenthoate peak shapes.*

for precooled sample did not necessarily increase the temperature of the system above 10°C and thereby proved very useful for maintaining the stability of the phthalimides such as captan.
