Analysis of Organophosphorous Pesticides in Produce by Solid/Liquid Extraction and Dual-Layer Amino-Silica/Carbon SPE Cleanup and GC-NPD

By: Olga Shimelis, Katherine Stenerson, Michael Ye, Carmen T. Sanatasania, Michael Monko, Reporter US Volume 28

Olga Shimelis, Katherine Stenerson, Michael Ye, Carmen T. Sanatasania, Michael Monko

olga.shimelis@sial.com

Introduction

Organophosphorous pesticide use in agriculture is widespread due to the fact that they are more amenable to environmental degradation in comparison to organochlorine or organonitrogen compounds. There is a large number of pesticides in the organophosphorous group, and because of their potential health effects, they are of particular concern on produce imported from areas in which they are commonly used. In this work we analyzed the representative organophosphorous pesticides from cabbage, green onions, apples and mushrooms. The extraction was performed using a custommade mixture of salts and liquid-liquid partitioning, with clean-up using dual-layer Supelclean ENVI-Carb-II/PSA Solid Phase Extraction (SPE) tubes.

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Sample Preparation

A 10 g homogenized food sample was spiked at 10 ng/g with pesticides, and 10 mL of acetonitrile was added. The sample was mixed with custom-made extraction salts – 4 g dry magnesium sulfate and 1 g sodium chloride. The sample was centrifuged and the supernatant was mixed with 1 g of dry magnesium sulfate. 5 mL of the resulting sample was evaporated down to 1mL for SPE loading. A Supelclean ENVI-Carb-II/PSA 500 mg/500 mg 6 mL tube was pre-conditioned with 5 mL acetonitrile:toluene (65:35). The sample was loaded and eluted with 10 mL of acetonitrile:toluene (65:35). The elution fraction was evaporated to 0.5 mL and reconstituted to 1mL with ethyl acetate.

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Conclusions

Most of the pesticides tested showed good recovery and reproducibility. Recoveries for some pesticides were still matrix-dependent, such as dichlorvos from cabbage (Table 1). GC analysis using an SLB-5ms column was optimized by using nitrogen phosphorus detection (NPD). Although NPD is highly sensitive for nitrogen containing compounds (such as organophosphorus pesticides), the high level of sulfur-containing compounds found in cabbage and onions still contributed to matrix interference as observed in Table 1. Custom-made mixes of extraction salts saved total sample preparation time.


Table 1. Percent Recovery and (% RSD) of Representative Organophosphorus Pesticides Spiked into Vegetables at 10 ng/g (n=3)

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