Milica Branković

The alteration in pesticides instrumental signal in complex samples analysis is defined as the matrix effect. The effect is a result of analytes and matrix components interaction within the injector, detector, or chromatography column and its level depends upon several factors such as the type of extraction solvent, clean-up, analyte concentration and chemical class, type and concentration of the matrix etc. The aim of this investigation was to assess the nature of the matrix effect in different matrices, by analysing different apple varieties and separately the peel and the flesh of a variety. Additionally, the possibility of the matrix effect minimization by dilution of sample extracts was investigated. Varietal differences in composition, as well as differences in the composition of peel and flesh, reflected in distinctive matrix effect for these matrices. The dilution seems to be promising approach for the matrix effect minimization. However, how much dilution is allowed depends on the desirable sensitivity of analysis.

As highly selective and sensitive, mass spectrometry currently stands for the most used analytical technique for both qualitative and quantitative analysis in many fields. One of the most significant factors in analytical calibration and quantification studies is sensitivity, which can be defined as the increment in measured signal per unit change in analyte concentration. Several factors such as the effective sample preparation, mobile phase composition, chromatographic column parameters and mass spectrometer features can affect analyte signal and result in various levels of sensitivity. The aim of this study was to evaluate calibration performances of the pesticides analysis in fruit and vegetable across the two instruments, by comparing the sensitivity on the two most exploited mass analyzers, that is on the linear ion trap and triple quadrupole mass analyzer. The comparison of sensitivity for solvent-based and QuEChERS treated lemonand lettuce-based pesticides standards demonstrated triple quadrupole as a highly sensitive instrument.

Frequent pesticide application, along with their health risk keep the need for continuous pesticides residue monitoring in food. Nowadays multiresidue pesticides analysis in complex matrices is mostly quantitative chromatography-based analysis. Methods that are primarily designed for qualitative analysis and exclude the usage of chromatography much less can be found in literature. Primary goal of this investigation was to launch a non-chromatography based direct infusion ESI/MS method designed for fast qualitative pesticides screening in fruit. The method was intended to be shorter and simpler than usual methods. As such, the method can be used in early stages in pesticides residues evaluation process, and the obtained results can decide whether to proceed evaluation with some quantitative method or do not.

The leading type of ionization technique in mass spectrometry analyses is the ionization at atmospheric pressure. The aim of this study was to assess ESI and APCI ionization efficiency of pesticides introduced to the MS source in four organic phases, non‐doped and doped with formic acid and ammonium formate. Ionization efficiency in modified ESI and APCI, applying in‐source sample heating, was also assessed. The study was primarily designed to support non‐chromatography‐based mass spectrometry pesticides analysis by the direct infusion technique. Evaluation of analysis performances such as calibration performances, detectability, and sensitivity should indicate a top solvent‐additive‐source combination, leading to the highest ionization efficiency and lowest analytes detection limits.

Green chemistry, green analytical chemistry and green sample preparation are related areas that have been developing since the 90s, aiming to moderate the adverse impacts of chemical practices on the environment and human health.

This research was focused on the performance evaluation of a simple sample preparation involving acetonitrile extraction followed by liquid chromatography/mass spectrometry (LC/MS) analysis. Simplified method validation parameters, along with several other features, were compared to those of the citrate QuEChERS for 19 pesticides analyzed in four representative fruits and vegetables. The results showed comparable performances of the two methods for 5 of the 6 investigated validation parameters. The simplified method had better performance regarding the selectivity, since three analytes experienced a selectivity issue in one of four QuEChERS-treated matrices. Overall, results lead to an assumption that acetonitrile extraction could be reasonably implemented in certain cases of pesticide analysis, as an efficient and economical alternative to the official method. Since the research provides an insight into acetonitrile extraction capabilities in the domain of pesticide analysis in complex matrices, scientists, researchers or analytical practitioners can determine which method is most beneficial for a particular analysis.

A fast and simplified method based on mass spectrometry analysis was developed for pesticide qualification in apple peel. The main feature of the method is flow-injection of the loop pre-defined sample volume directly to the MS source, with no chromatographic separation. Method performances were evaluated for five pesticides regularly used in apple orchard treatments. First, primary features of the method such as the loop injection dynamics, total analysis time, chronogramic peaks integrity and sensitivity were evaluated. Then the applicability of the method for qualitative and quantitative screening was assessed on citrate buffered QuEChERS cleaned-up apple peel samples. The developed method offers a possibility for simplified, more economic high throughput screening for pesticides in apples. The method is intended to be a tool for preliminary qualitative assessment of pesticides residues in fruit. Quantitative features of the method are analyte and sample preparation dependent, most certainly due to the lack of chromatography.

Gas chromatography coupled with mass spectrometry (GC/MS) is commonly applied in pesticide residue analysis in fruit samples. Sample extracts with a high quantity of co-extractives represent a standing problem in such analysis. Co-extractives mainly affect the GC inlet and the chromatographic column performance. Waxes, identified as the main co-extractives from the apple matrix, represent a significant problem in GC/MS analysis due to low volatility and non-polarity. The purpose of this investigation was to develop and evaluate a simplified method for the analysis of boscalid in apples, with the removal of wax compounds as the main outcome. The waxes herein represented a problem not only for the performance of the instrument but directly for the determination of the boscalid since they co-eluted with the pesticide. The applied method included a combination of solvent exchange and low-temperature precipitation and resulted in complete wax removal.