Abstract
An effective pre-concentration method, namely amended-cloud point extraction (CPE), has been developed for the extraction and pre-concentration of neonicotinoid insecticide residues. The studied analytes including clothianidin, imidacloprid, acetamiprid, thiamethoxam and thiacloprid were chosen as a model compound. The amended-CPE procedure included two cloud point processes. Triton™ X-114 was used to extract neonicotinoid residues into the surfactant-rich phase and then the analytes were transferred into an alkaline solution with the help of ultrasound energy. The extracts were then analyzed by high-performance liquid chromatography (HPLC) coupled with a monolithic column. Several factors influencing the extraction efficiency were studied such as kind and concentration of surfactant, type and content of salts, kind and concentration of back extraction agent, and incubation temperature and time. Enrichment factors (EFs) were found in the range of 20–333 folds. The limits of detection of the studied neonicotinoids were in the range of 0.0003–0.002 µg mL−1 which are below the maximum residue limits (MRLs) established by the European Union (EU). Good repeatability was obtained with relative standard deviations lower than 1.92% and 4.54% for retention time (tR) and peak area, respectively. The developed extraction method was successfully applied for the analysis of water samples. No detectable residues of neonicotinoids in the studied samples were found.
Highlights
Neonicotinoids have been commercialized as a new generation of pesticides affecting the central nervous system of insects, whilst they exert a lower neurotoxicity towards mammals than previously developed insecticides [1]
Neonicotinoid insecticides act as agonists at the insect nicotinic acetylcholine receptors, which play an important role in synaptic transmission in the central nervous system [5]
High precision was observed with relative standard deviation (RSD) lower than 2.00 and 5.00, respectively. These results show that the developed extraction method coupled to high-performance liquid chromatography (HPLC) can increase the sensitivity of detection
Summary
Neonicotinoids have been commercialized as a new generation of pesticides affecting the central nervous system of insects, whilst they exert a lower neurotoxicity towards mammals than previously developed insecticides [1]. Neonicotinoids were developed as a safer and more effective class of pesticides [2], and as a result they have become the most popular group of insecticides with applications in agriculture and veterinary medicine [1] instead of other classes of pesticides, including organochlorines, organophosphates and carbamates. This group of insecticides includes nitro-substituted (dinotefuran, nitenpyram, thiamethoxam, imidacloprid and clothianidin) and Molecules 2018, 23, 1165; doi:10.3390/molecules23051165 www.mdpi.com/journal/molecules. A highly sensitive and selective analytical method for monitoring neonicotinoid residues at low concentration levels is required to secure food quality and to protect the consumer from hazards
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