Extraction of Permethrin Pesticides from Spinach Using QuEChERS Methodology with Automated Shaking

Introduction

Sample preparation procedures for pesticide analysis in fruits and vegetables were simplified with the introduction of QuEChERS methodology in 2003.¹ Multi-residue pesticide extraction was accomplished through a 1 minute shaking procedure using acetonitrile as an extraction solvent followed by salt partitioning and dispersive solid phase extraction (SPE) cleanup. This extraction procedure has been successfully applied to a variety of fruits and vegetables. The QuEChERS procedure has grown in popularity and has gained worldwide acceptance during the past 10 years.

It is common to evaluate and validate pesticide residue methods by spiking representative blank matrix samples with a standard mix of pesticides. Pesticide-free produce samples, such as organically grown produce, are often used for this purpose. The pesticides are typically added to a matrix sample 1-2 hours prior to testing in order to allow pesticide incursion. They are then easily extracted using the 1 minute shaking protocol. However, recently, it was noted that existing residues may not be readily accessible for extraction as they can be “enclosed into cells or wax particles” of the produce.² The 1 minute shaking time specified in the QuEChERS protocol was not sufficient to fully extract existing pesticide residues in approximately 50% of tests conducted. It was later observed that a 10-15 minute shaking time with the use of an automated shaker was required to obtain acceptable extraction efficiencies.³