ABSTRACT
A reliable 16-min analytical method for the simultaneous determination of 250 pesticides in processed fruit using ultra-performance liquid chromatography, coupled to tandem mass spectrometry (UHPLC-MS/MS), was developed and validated according to SANTE 11813/2017 guidelines and accredited successfully based on ISO 17025. Extraction was achieved using a modified QuEChERS method, without any clean-up, including a dilution to obtain good peak shapes and to reduce matrix effects. Pesticides were quantified using matrix-matched calibration, and the method was validated in terms of relative retention time window, linearity (6-167 µg kg-1 and 0.6-16.7 µg kg-1, coefficient R2 ≥ 0.98), trueness (recovery of 70-120%), selectivity, precision (RSD ≤ 20%), limits of quantification (LOQs = 0.6-6.0 µg kg-1) and uncertainty. Finally, the method was applied to the routine analysis of 103 samples of processed fruits, detecting the presence of several pesticide residues, such as fluopyram, spinosad or cyprodinil (0.006-0.22 mg kg-1).
Subject(s)
Fruit/chemistry , Pesticide Residues/analysis , Calibration , Chromatography, High Pressure Liquid , Reproducibility of Results , Tandem Mass SpectrometryABSTRACT
A simple, selective and sensitive method has been developed for the simultaneous determination of tetracycline, oxytetracycline, chlorotetracycline, demeclocycline, doxycycline and meclocycline based on reversed-phase high-performance liquid chromatography with chemiluminescence detection. The procedure was based on the chemiluminescent enhancement by photoirradiated tetracyclines of the cerium (IV)-rhodamine B system in sulphuric acid medium. The six tetracyclines were separated on an Aquasil-C18 column with a gradient elution using a mixture of acetonitrile and 0.1 mol L(-1) phosphate buffer as mobile phase, photoderivatized using a photoreactor consisting of a tube reactor coil of PFA and a 8W Xenon lamp. Under the optimized conditions, the method was validated with respect to linearity, precision, limits of detection and quantification and accuracy. The relative standard deviation (RSD) on intra-day precision was below 10% and detection limits ranged between 0.12 and 0.34 microg L(-1). The proposed method has been successfully applied to the determination of tetracyclines in surface water samples. A possible mechanism of the chemiluminescence in the system is discussed.
Subject(s)
Cerium/chemistry , Chromatography, High Pressure Liquid/instrumentation , Chromatography, High Pressure Liquid/methods , Luminescent Measurements/methods , Organometallic Compounds/chemistry , Rhodamines/chemistry , Tetracyclines/isolation & purification , Indicators and Reagents , Kinetics , Molecular Structure , Photochemistry , Sensitivity and Specificity , Tetracyclines/chemistry , Water/chemistryABSTRACT
The viability of tandem photochemical reaction-chemiluminescence detection has been studied for the determination of five benzoylurea insecticides, namely, diflubenzuron, triflumuron, hexaflumuron, lufenuron and flufenoxuron. The 'on-line' photochemical reaction of benzoylurea pesticides provides an enhanced chemiluminescence response of the pesticides during their oxidation by potassium hexacyanoferrate(III) and sodium hydroxide, whose signal increases with the percentage of acetonitrile in the reaction medium. The determination was performed using a photoreactor consisting of a PFA (perfluoroalkoxy) tube reactor coil (5 mx1.6-mm O.D. and 0.8-mm I.D.) and an 8-W xenon lamp. As the yield of the photoderivatization process and the chemiluminescent signals depend on the percentage of acetonitrile, the chromatographic column (a Gemini C18, Phenomenex 150 mmx4.6 mm, 5-microm particle size) was chosen with the aim of using high percentages of this organic solvent in the mobile phase. Previous studies showed that the rate of the chemiluminescent reaction was very fast. Therefore, a modification was carried out in the detector in order to mix the analytes and reactants as near as possible to the measure cell. The optimised method was validated with respect to linearity, precision, limits of detection and quantification accuracy. Under the optimised conditions, linear working range extends three orders of magnitude with the relative standard deviation of intra-day precision below 10% and detection limits between 0.012 and 0.18 microg mL-1, according to the compound. The proposed method has been successfully applied to the determination of benzoylureas in cucumber with good results.
