Pesticide-residue analysis sample treatment

Despite the important advances in fast LC, food matrices are very complex, and although in general multi-residue methods with minimal sample manipulation are demanded, sample extraction and clean-up treatments must be carefully developed to also reduce the total analysis time. The most recently introduced sample treatment methodologies for pesticide residue analysis have also been addressed, with QuEChERS being the most popular one for its easy application and good results. However, other alternatives, such as online SPE or the use of more selective methods such as MIP, are also being applied for the analysis of pesticides. 

Gilbert-Lopez, B., Garcfa-Reyes, J. F., Fernandez-Alba, A. R., and Molina-Dfaz, A. 2010. Evaluation of two sample treatment methodologies for large-scale pesticide residue analysis in ohve oil by fast hquid chromatography-electrospray mass spectrometry. J. Chromatogr. A 1217 3736-3747. 

This chapter focuses on LC—MS/MS applied to pesticide residue analysis, as this technique is the most attractive and efficient nowadays for developing MRMs [11], including both parent pesticides and metabolites. Sample treatment (mainly extraction and cleanup) are briefly commented on, with emphasis on those commonly applied in MRMs. A brief mention is made of problematic pesticides that do not fit in MRMs and consequently need to be determined with individual-specific LC—MS/MS methods. The use of HR MS in combination with LC also is briefly treated, either for the investigation of parent pesticides or for metabolite research, as this is a field of major interest at present. 

Some aspects of the sources, occurrence, and dispersion of airborne pesticide residues (6, 27) and methods for their sampling and analysis (28, 29, 30, 31) have been reviewed elsewhere. In this paper, the focus will be on sampling methodology, experimental design, and some results from recent field tests aimed at determining the entry and proximate fate of airborne residues in relation to specific agricultural treatments. 

Nevertheless, due to the increased number of pesticides used worldwide and the variety and eomplexity of food matrices, the use of ultra-fast separations is not enough to develop fast analytical methods for the analysis of pesticide residues in food. Besides, multi-residue screening methods able to analyze not only target but nontarget or even unknown compounds, minimizing the sample manipulation, are dananded. Thus, sample extraction and clean-up treatments must also be optimized when considering... 

In addition, when dealing with the multi-residue analysis of pesticides in such complex matrices as foodstuff, the reduction of the total analysis time because of both fast UHPLC separations and simple sample treatments may CTeate new analytical challenges. More matrix-related compounds may be introduced into the chromatographic system due to the simplification on sample treatment and, although high resolution and separation efficiency is achieved by UHPLC, matrix effects (ion suppression or ion enhancement) may occur. MS or MS/MS is then mandatory, but, in some cases, alternative confirmation and identification strategies [17] and HRMS will be required [29]. 

The aim of this chapter is to present the state of the art on UHPLC-MS(/MS) analysis of pesticides in food. It includes a selection of the most relevant papers recently published regarding instrumental and column technology focusing on UHPLC analysis with sub-2 pm and novel porous shell particle-packed columns. Sample treatment procedures such as QuEChERS, MIPs, and online SPE will also be addressed. MS strategies for the analysis of pesticide residues as well as to guarantee confirmation and identification such as the use of HRMS or alternative confirmation strategies will be discussed with relevant application examples. 

A matrix has been shown to affect the signal for most of the pesticides analyzed in multiple matrices, despite the high resolution offered by UHPLC and sample treatment based on QuEChERS, pressurized solvent extraction, SPE, or a combination of both [75,77,78,80,82,83,89,90]. The most common way to overcome this issue has been quantifying with a matrix matched in agreement with the SANCO guidelines [91], which has been the quantification strategy followed by many authors. The high number of pesticides analyzed in multi-residue analysis does not make feasible the use of standard addition, which would increase the analysis time and materials needed or the use of labeled internal standards, which would make the analysis very expensive as well as increase the number of transitions to follow when triple... 

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