Analytical MethodsDevelopment, validation and determination of multiclass pesticide residues in cocoa beans using gas chromatography and liquid chromatography tandem mass spectrometry
Introduction
Currently, Malaysia is the largest cocoa processor in Asia and ranks fifth in the world with a volume of 293,000 tonnes in 2013 (International Cocoa Organization., 2014). Unfortunately, due to the shortage of locally produced beans (2809 tonnes), Malaysia had to import 311,608 tonnes of dried cocoa beans mainly from Indonesia and Africa to meet the growing local grindings requirement (Malaysian Cocoa Board, 2014). Hence, food safety played an important role in cocoa industry since the originality of the agrochemicals used in the exporting countries is unknown.
The identification of pesticide residues in food with high fat content such as cocoa beans is a difficult and challenging task since the inherent complexity of the matrix could interfere in the determination and quantification of the targeted analyte of interests. Among other constituents contained in cocoa beans are high amount of fatty acids, fatty acid esters, phytosterols, tocopherols, sugar, polyphenols, theobromine, and caffeine. It is well known that the main problem associated when dealing with these kinds of matrices for analysis is that dirty extracts with even a small amount of fats may disrupt the analytical column used in the experiment and harm the analytical instrument ion sources and detectors, and finally upsetting the correct analyte determination through signal suppression and enhancement. Hence, the development of sensitive, selective and reproducible analytical method and technique have always been a prerequisite for the achievement of high quality results in enforcement and monitoring programme (Pizzutti, de Kok, Hiemstra, Wickert, & Prestes, 2009).
While the number of publications on the determination of pesticide residues in vegetables, fruits and other foodstuffs were extensive (van der Lee, van der Weg, Traag, & Mol, 2008), the number of papers dedicated to cocoa beans analysis is relatively limited (Rodríguez et al., 1991, Hirahara et al., 2005, Guan et al., 2009, Frimpong et al., 2012a, Paul et al., 2012, Frimpong et al., 2012b, Ademola and Gideon, 2012). Rodríguez et al. (1991) studied the identification and determination of some organophosphorus and organochlorine pesticides in cocoa beans by gas chromatography mass spectrometry (GC–MS) using Universal Trace Residue Extractor (UNITREX). In another study, Hirahara et al. (2005) reported a validation of multiresidue screening method for the determination of 186 pesticides in 11 agricultural products including cocoa beans using a combination of solvent extraction and solid phase extraction (SPE) clean-up with mini column (SAX/PSA). Guan et al. (2009) published a new approach to multiresidue pesticide determination in foods with high fat content using disposable pipette extraction (DPX) and determination with GC–MS. Several papers also appeared on the determination of organochlorine (Frimpong et al., 2012a, Paul et al., 2012), synthetic pyrethroid (Frimpong et al., 2012b) and organophosphorus (Ademola & Gideon, 2012) residues employing a combination of solvent extraction and SPE clean-up.
Until now, there are very few studies on the method and level of pesticide residues in cocoa beans. Most of the current methods discussed above involve high volume of extraction solvent, long sample preparation time, and required specialised materials or instrumentation. Furthermore, some of the current methods are focused only to certain classes of pesticides. Therefore, the need for a fast, robust and efficient method for the determination of pesticide residues of different chemical classes in cocoa beans is evident. For this reason, the purpose of this work was to develop and validate an efficient and rapid method for the analysis of different classes of pesticide residues in cocoa beans. Finally, the optimised method was then applied in a real sample monitoring programme carried out on imported and domestic cocoa beans samples collected over two years from smallholders and Malaysian ports.
Section snippets
Reagents and materials
HPLC grade acetonitrile and reagent grade formic acid were obtained from Merck (Darmstadt, Germany) while reagent grade ammonium formate was obtained from Sigma–Aldrich (St. Louis, USA). Water was purified through an Elga Purelab Option-Q system (High Wycombe, UK). Two mL mini-centrifuge tube containing 150 mg MgSO4, 50 mg C18, and 50 mg primary secondary amine (PSA) was purchased from Agilent Technologies (Palo Alto, USA).
Pesticide reference standards of all analytes were purchased from Dr.
Optimisation of LC–MS/MS parameters
Initially, a Q1 scan of the mass spectra was recorded to select the most abundant mass to charge ratio (m/z) ion using continuous infusion of each pesticide directly into the MS using syringe pump at a flow rate of 10 μL/min. In this study, the proton adduct [H+] of the molecular ion was chosen as the precursor ion for all analytes. Then, enhance product ion (EPI) scan was conducted to obtain the product mass spectra of the precursor ion. The first transition, which corresponds to the most
Conclusions
According to Malaysian Food Act and Regulations (Food Regulations, 2010), there are a total of 34 pesticides allowed to be use in cocoa plantation with national MRLs regulated. Out of these 34 pesticides, 26 pesticides were covered in this study. The rest of the pesticides were either belong to difficult pesticides (dithiocarbamate, fosetyl ammonium, MSMA) or highly polar pesticides (glufosinate, glyphosate, paraquat), hence require specific single residue method (SRM). Reliable, efficient and
Acknowledgements
The authors would like to thank the Malaysian Cocoa Board (MCB) for financially supporting this work and the Director General of the MCB for permission to publish this paper. The authors are also highly indebted to the Regulatory and Quality Control Division for providing the monitoring samples for analysis.
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