Extraction of Residual Chlorinated Pesticides from Cotton Matrix as Part of a Certification Method for Cotton Reference Material

As a part of developing a certified testing method for residual pesticides analysis in cotton materials using gas chromatography (GC), the target pesticides listed in Oko-tex standards should be isolated from a homogenized cotton matrix. The sample homogeneity and extraction procedures are the most effective steps in this analysis. Any error in this procedure must lead to incorrect results. Two extraction methods with different solvents, e.g., methanol, hexane, hexane/acetone (1:1 v/v), and dichloromethane were used throughout this work. Extraction methods were soxhlet (SOX) and accelerated solvent extraction (ASE). The resulted extracts were concentrated then injected into a GC equipped with an Electron Capture Detector (ECD). The qualitative results, when compared with those of the NIST standard reference material (SRM-2261) certified by the National Institute of Standards and Technology, USA, proved that the ASE and SOX techniques with dichloromethane as extracting solvent are more selective for all concerned pesticides for homogenized cotton samples. The ASE extraction with dichlormethane is better for hexachlorobenzene, gamma-HCH, heptachlor, Cis-chlordane, trans-nonchlor, and SOX extraction technique with dichloromethane is better for Heptachlor epoxide, 4,4′-DDE, Dieldrin, 2,4′-DDD, 4,4′-DDT, and Mirex with broading in the resulted peaks.