Mixed surfactant systems based on primary amine and medium-chain fatty acid: Micelle-mediated microextraction of pesticides followed by the GC–MS determination

Highlights

• Mixed surfactant system based on primary amine and medium-chain fatty acid

• Non-viscous surfactant-rich phase compatible with GC–MS system

• Novel micelle-mediated microextraction coupled with GC–MS

• New mixed surfactant system for fast pesticides extraction from food samples

Abstract

Mixed surfactant systems based on primary amine and medium-chain fatty acid were investigated and used for the micelle-mediated microextraction for the first time. It was established, that injection of the mixture of primary amine and medium-chain fatty acid into an aqueous sample phase led to formation of a micellar solution. The obtained micellar solution can be used for analytes separation from solid food samples. The addition of salting-out agent into the micellar solution promoted formation of non-viscous surfactant-rich phase and extraction of analytes. The surfactant-rich phase obtained after centrifugation was found to be compatible with a gas chromatography–mass spectrometry (GC–MS) system without any dilution to reduce phase viscosity. Various primary amines and medium-chain fatty acids were studied for the micelle-mediated microextraction from sample suspension and the system based on 1-nonylamine and pivalic acid (3: 2, v/v) was evaluated as the most effective. The surfactant-rich and aqueous phases were investigated in detail to reveal the mechanism of the proposed microextraction procedure. A novel micelle-mediated microextraction for the determination of pesticides (diazinon, triadimefon, triadimenol and bifenthrin) in food samples by GC–MS was developed. The limits of detection, calculated from blank test, were established to be 8 μg kg⁻¹ for diazinon, 10 μg kg⁻¹ for triadimefon, 5 μg kg⁻¹ for triadimenol, and 1 μg kg⁻¹ for bifenthrin. The microextraction procedure can be characterized as fast (7 min), simple and cheap.

Introduction

The use of pesticides in modern agriculture is the most widespread way to protect plants from pests due to the rapid application over the large areas, high efficiency and low cost considering its low working concentrations. Despite these advantages, pesticides can cause the negative impact on the environment such as phytotoxicity and massive death of beneficial insects and animals. Excessive use of these substances leads to serious human health disorders including allergic reactions, cancer tumors, birth defects and neurological damage [1]. Therefore, concentrations of pesticides in edible plants and plant-based food have to be under control to prevent above-mentioned undesirable effects on humans and environment.

High-performance liquid chromatography (HPLC), gas chromatography (GC) or capillary electrophoresis combined with mass-spectrometry (MS) as well as immunoassay are the most frequently used analytical methods for the determination of different pesticides in various samples [2]. It should be noted, that various electrochemical, optical and piezoelectric sensors are also used for this analytical challenge, but their sensitivity and life-time are often limited [3].

Taking into account the complexity of food sample matrices the pretreatment of samples is required. It helps to eliminate matrix interference and increase sensitivity by pre-concentration. Various liquid-liquid extraction (LLE), solid-phase extraction (SPE) and well-known QuEChERS techniques are usually applied for the extraction and pre-concentration of pesticides [4]. Conventional LLE and SPE techniques are usually tedious, time-consuming and require large volumes of toxic organic solvents.

Micelle-mediated microextraction can be considered as an environmentally friendly and inexpensive alternative to the existing methods. It is based on the ability of surfactant molecules at sufficient concentration to form micelles in aqueous solution, which can extract hydrophobic compounds. Surfactant-rich phase can be separated by changing temperature, ionic strength or pH, with subsequent determination of the analytes in the extract. Various surfactant (non-ionic [[5], [6], [7]], anionic [8], cationic [9] and mixed [10]) systems have been reported for the preconcentration of pesticides from environmental, food and biological samples (Table 1). One of the limitations of the procedures proposed is high viscosity of the surfactant-rich phase, which is unacceptable for direct injection into a liquid or gas chromatography equipment. Usually in order to reduce viscosity of the surfactant-rich phase its dilution [[8], [9], [10], [11], [12], [13], [14]], precipitation [6] or re-extraction [5,15] is implemented. Such procedures can reduce sensitivity due to dilution effect and require additional reagents and solvents and can be time-consuming. The search for new effective surfactant systems has interest in sample pretreatment based on the micelle-mediated microextraction.

In this work, it was found that mixed surfactant systems based on primary amine and medium-chain fatty acid promote formation of non-viscous surfactant-rich phases caused by changes in the ionic strength. To the best of our knowledge, the application of such systems for micelle-mediated microextraction has not been presented in literature. In this research, the surfactant-rich phases obtained after phases separation were withdrawn into a conventional chromatographic syringe and injected directly into a gas chromatography–mass spectrometry (GC–MS) system without any dilution to reduce phase viscosity. A novel approach was implemented for the micelle-mediated microextraction of pesticides (diazinon, triadimefon, triadimenol and bifenthrin, Fig. 1) from food samples followed by the GC–MS determination. Studied analytes are widely used in agriculture in different countries including Russia and their concentrations are strictly regulated in foods [16,17].