Susana Grimalt

Collision-induced dissociation of 3-keto anabolic steroids and related compounds after electrospray ionization. Considerations for structural elucidation

The collision-induced dissociation of forty-one 3-keto anabolic steroids and related compounds has been studied using both triple quadrupole (QqQ) and hybrid quadrupole-time of flight (QTOF) instruments. Due to the complexity of the product ion spectra of these analytes, which generate a large number of ions, only two specific regions were studied in depth: the product ions near the precursor ion (m/z > or =M-100) and the most abundant product ions at a collision energy of 30 eV. Accurate mass measurements were used in order to obtain an unequivocal assignment of the empirical formula and the origin of each selected product ion. Analytes have been divided into eight groups according to the number and position of double bonds and the presence of functional groups such as hydroxyl- or nitrogen-containing rings. A correlation between the steroid structure and the product ions obtained has been postulated. The application of these correlations can be useful in the elucidation of feasible structures for unknown steroids and/or their metabolites.

Quantification, confirmation and screening capability of UHPLC coupled to triple quadrupole and hybrid quadrupole time-of-flight mass spectrometry in pesticide residue analysis.

The potential of three mass spectrometry (MS) analyzers (triple quadrupole, QqQ; time of flight, TOF; and quadrupole time of flight, QTOF) has been investigated and compared for quantification, confirmation and screening purposes in pesticide residue analysis of fruit and vegetable samples. For this purpose, analytical methodology for multiresidue determination of 11 pesticides, taken as a model, has been developed and validated in nine food matrices for the three mass analyzers coupled to ultra high pressure liquid chromatography. In all cases, limits of quantification around 0.01 mg/kg were reached, fulfilling the most restrictive case of baby-food analysis. Regarding absolute sensitivity, the lower limits of detection were obtained, as expected, for QqQ (100 fg), whereas slightly higher limits (300 fg) were obtained for both TOF and QTOF. Confirmative capacity of each analyzer was studied for each analyte based on the identification points (IPs) criterion, useful for a comprehensive comparison. QTOF mass analyzer showed the highest confirmatory capacity, although QqQ normally led to sufficient number of IPs, even at lower concentration levels. The potential of TOF MS was also investigated for screening purposes. To this aim, around 50 commercial fruits and vegetables samples were analyzed, searching for more than 400 pesticides. TOF MS proved to be an attractive analytical tool for rapid detection and reliable identification of a large number of pesticides thanks to the full spectrum acquisition at accurate mass with satisfactory sensitivity. This process is readily boosted when combined with specialized software packages, together with theoretical exact mass databases. Several pesticides (e.g. carbendazim in citrus and indoxacarb in grape) were detected in the samples. Further unequivocal confirmation of the identity was performed using reference standards and/or QTOF MS/MS experiments.

Use of ultra‐high‐pressure liquid chromatography–quadrupole time‐of‐flight MS to discover the presence of pesticide metabolites in food samples

In this paper we illustrate the use of two different methodologies to investigate the presence of pesticide metabolites in parent pesticide-positive food samples, using ultra-high-pressure liquid chromatography coupled to hybrid quadrupole time-of-flight (UHPLC-QTOF) mass spectrometry. First, a common fragmentation pathway between the parent pesticide and its metabolites has been considered to search for metabolites in two positive market samples (imazalil in lemon, chlorpyrifos in grape). Secondly, olive oil samples from field residue trials were used for automated application of comparative software (MetaboLynx), which was used with treated and untreated samples to search for expected and unexpected metabolites of phosmet. One of the main objectives when using these approaches was to avoid the tedious manual searching for potential metabolites within the huge amount of information contained in the total ion chromatogram acquired by TOF MS. The common fragmentation approach applied to TOF MS full-acquisition data, considering an enhanced fragmentation in the collision cell, has allowed the discovery of two metabolites of imazalil (1-[2-(2,4-dichlorophenyl)-2-hydroxyethyl]-1H-imidazole and 1-[2-(2,4-dichlorophenyl)-2-oxoethyl]-1H-imidazole) in a lemon positive sample, as well as another two metabolites of chlorpyrifos (chlorpyrifos-oxon and 3,5,6-trichloro-2-pyridinol) in a grape positive sample. Moreover, MetaboLynx application to TOF MS data, without promoting fragmentation, from treated and untreated olive oil samples has been helpful in detecting the metabolite phosmet-oxon. In both strategies, every metabolite detected by TOF MS was confirmed using QTOF and/or triple quadrupole instruments. Accurate masses given by TOF MS together with the valuable information on product ions given by QTOF MS/MS experiments were crucial for the unambiguous identification of metabolites.

Residue levels of captan and trichlorfon in field-treated kaki fruits, individual versus composite samples, and after household processing.

The dissipation of residue levels of captan and trichlorfon in field-treated kaki crops was studied according to good laboratory practices to propose maximum residue limits (MRLs). Residue levels of captan and trichlorfon were analysed by GC/MS and LC-MS/MS, respectively. Residue levels of captan and trichlorfon permitted one to propose MRLs in kaki of 3 and 5 mg kg−1, respectively. The behaviour of these residues was also studied after peeling and cooking, and in individual fruits versus composite samples. Residue levels of these compounds for individual fruits suggested that a variability factor up to three could be set for the acute risk assessment. Levels of captan decreased by more than 90% after peeling and completely after cooking. Trichlorfon penetrates into the flesh in a proportion of 70% of the residue at the pre-harvest interval. Cooking resulted in a decrease of 27% of residue levels of trichlorfon.