The control of pesticide residues in food is required by law to assure human food safety and safeguard the consumers’ health. In Europe, maximum residue limits (MRL) of pesticides permitted in products of animal or vegetable origin that are intended for human consumption have been established by Regulation (EC) No. 396/2005 of the European Parliament and Council on pesticide residues. Nowadays, gas chromatography coupled to mass spectrometry (GC-MS, GC-MS/MS) with electron impact ionization (EI) and liquid chromatography-tandem mass spectrometry (LC-MS/MS) with electrospray ionization (ESI) are techniques most often employed for multiresidue pesticide analysis in food due to their high sensitivity and selectivity, ability to screen many pesticides from various chemical classes in very complex matrixes in a single run. The former may be used only for the analysis of volatile chemicals; thus, the analyzed pesticide has to be volatile or amenable to derivatization to ensure its volatility. GC-MS is a method of choice for less polar pesticides; for more polar compounds, LC-MS is more suitable. The need to deal with more polar pesticides as well as with pesticide metabolites, which are often more polar and less volatile than pesticide itself, is one of the main reasons for choosing LC-MS/MS over GC-MS. Compounds which are thermolabile, not volatile, and have not been derivatized can be separated by LC-MS. LC-MS can analyze a much wider range of chemicals than GC-MS. The thorough discussion on application of GC-MS, GC-MS/MS, and LC-MS/MS for the analysis of different chemical classes of pesticides can be found in the book chapter by Raina (2011). The assessment for the evaluation of the capabilities of GC-MS(/MS) and LC-MS/MS for the determination of pesticides carried out by Alder et al. (2006) and Carmona et al. (2013) showed that a wider scope and better sensitivity is achieved by LC-MS.
The wide scope of pesticides covered and simple sample preparation is the key reason why liquid chromatography coupled to mass spectrometry is more and more frequently used for the detection, identification, and quantification of pesticides in food nowadays. This technique provides information about the structure of the analyte, without the need to derivatize the analyte. Its sample purity requirements are not stringent, and it enables a simultaneous analysis of substances that vary considerably in polarity. The popularity of the method is confirmed by the increasing number of publications dedicated to the applications of LC-MS in the determination of contaminants, including pesticides, in food (Sivaperumal et al. 2015; Gómez-Pérez et al. 2015; Martinez-Dominguez et al. 2015; Golge and Kebak 2015; Fillatre et al. 2014; Esturk et al. 2014; Oshita and Jardim 2014; González-Curbelo et al. 2014; Rajski et al. 2013; Arienzo et al. 2013; Stachniuk and Fornal 2013; Sinha et al. 2012; Gilbert-Lopez et al. 2012; Lozano et al. 2012; Chung and Lam 2012; Botero-Coy et al. 2012; Tian 2011; Pareja et al. 2011; Kmellar et al. 2011; Aguilera-Luiz et al. 2011; Chen et al. 2011; Lehotay et al. 2010; Zhang et al. 2010; Camino-Sanchez et al. 2010; Kamel et al. 2010; Brutti et al. 2010). In pesticide residue analysis, similarly to the analysis of other food contaminants, there is a distinct tendency to develop fast multiresidue methods.
In a typical LC-MS system, the sample analyzed is initially separated in the LC system and its successive fractions eluted from the chromatographic column are subjected to ionization and introduced into the spectrometer. Nowadays high-performance liquid chromatography (HPLC) and ultra high-performance liquid chromatography (UHPLC) are usually employed for the separation of analytes.
Multiresidue liquid chromatography-mass spectrometry methods (LC-MS) are widely recognized as an ideal, highly specific, and extremely sensitive technique for testing food products. This review discusses LC-MS approaches applied most widely to pesticide residue analysis over the last few years. Apr 8, 2016 - selectivity, GC and HPLC are the most frequently used methods for the detection. The determination of pesticide residues in real samples is often well beyond. Vidal, L.; Riekkola, M.-L.; Canals, A. Ionic liquid-modified.
The paper presents the elements of the LC-MS systems and discusses mobile phases, sorbents, types of MS analyzers, and ion detection techniques most frequently used in the analysis of pesticide residues in food. Besides the advantages of using LC-MS systems, the limitations of the method, resulting mainly from the matrix effect, and the means of minimizing its impact are discussed.
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The use of pesticides on crops grown for food is a controversial topic. Farmers and food supply companies are keen to get the maximum yield from the land to keep production costs down and to maximise profits; whilst environmentalists are worried about the effect of too many pesticides on the environment and consumers are worried about the effect of too many pesticides on their health.
In a battle that will have many twists and turns — especially if the UK relaxes the rules on pesticide use post-Brexit — it is up to chromatography to provide the data on the nasties that might be lurking on our plate. But which method is best for measuring the pesticides in our food?
Pesticides — a deeper look
Pesticides get rid of pests. The United States Environmental Protection Agency (EPA) defines pesticides as ‘any substance or mixture of substances intended for preventing, destroying, repelling, or mitigating any pest’. This includes insects, weeds or unwanted plants and fungi.
The EPA uses four classes of chemical pesticides:
- Organophosphorus pesticides work by disrupting the neurotransmitter enzyme acetylcholinesterase. They break down on exposure to air and sunlight.
- Organochlorine pesticides act by interfering with insect neurons.
- Carbamate pesticides are esters of carbamic acid. There are many different types and they have many uses including as fungicides, insecticides and herbicides. They are broken down in the environment within weeks.
- Pyrethroid pesticides are analogues of pyrethrin’s produced in flowers. They are widely used in insecticides.
The EPA has approved over 10,000 different types of pesticides using ‘conditional registration’ in the last decade — there are approximately 16,000 different pesticides known. Conditional registration is a fast track scheme on means that all the active ingredients might not have been fully tested for safety or environmental impact.
Chromatography analyses the residues
With so many potential pesticides in widespread use — multiresidue pesticide analysis is one of the main requirements in pesticide testing. And it seems that gas and liquid chromatography are both necessary for a complete picture along with tandem mass spectrometry in the ion transition mode.
Screening samples for so many possible ‘unknowns’ in a sample requires a comprehensive approach — particularly as the pesticides may have many different physiochemical properties. If the test is for a specific pesticide, then the task is much simpler and a search of a method database will show which method is recommended. The QuEChERS method was developed to help in the analysis of pesticides — and is now used in other types of analysis.
As consumers become more aware of what they are eating — the challenges for pesticide analysis will increase, a topic discussed in the article, Challenges Facing Pesticide Analysis and Monitoring - An Interview with Dr. Simone Hasenbein.