Biomedical subjects

Juan F García-Reyes

Publications and source records attributed to Juan F García-Reyes.

7 recordsLinked to original sources

PubMed2007

Identification of pesticide transformation products in food by liquid chromatography/time-of-flight mass spectrometry via "fragmentation-degradation" relationships.

The identification of transformation products of pesticides in foodstuffs is a crucial task difficult to tackle, due to the lack of standards and scarce information available. In this work, we describe a methodology for the identification and structural elucidation of pesticide transformation products in food. The proposed strategy is based on the use of liquid chromatography electrospray time-of-flight mass spectrometry (LC/TOFMS): accurate mass measurements of (molecule and fragment) ions of interest are used in order to establish relationships between fragmentation of the parent pesticides in the instrument (in-source CID fragmentation) and possible degradation products of these pesticides in food. Examples of this strategy showing the potential of LC/TOFMS to determine unknown pesticides in food are described in two different real samples, suggesting that pesticides often are transformed into degradation products in the same fashion that they are fragmented in the instrument. Using the proposed approach and without using standards a priori, based solely on accurate mass measurements of ions and "fragmentation-degradation" relationships, we have identified two parent pesticides (amitraz and malathion) along with six degradation products, m/z 253 (N,N'-bisdimethylphenylformamidine), 163 (N-2,4-dimethylphenyl-N-methyl formamidine), 150 (2,4-dimethylformamidine), and 122 (2,4-dimethylaniline) from amitraz, and m/z 317 and 303, due to ether hydrolysis of methyl and ethyl groups from malathion. Structures for these species were proposed, and the potential of the proposed approach was critically discussed.

Amidines↗

PubMed2006

Analysis of herbicides in olive oil by liquid chromatography time-of-flight mass spectrometry.

The application of liquid chromatography time-of-flight mass spectrometry (LC/TOF-MS) for the identification and quantitation of four herbicides (simazine, atrazine, diuron, and terbuthylazine) in olive oil samples is reported here. The method includes a sample treatment step based on a preliminary liquid-liquid extraction followed by matrix solid-phase dispersion (MSPD) using aminopropyl as a sorbent material. A final cleanup step is performed with florisil using acetonitrile as an eluting solvent. The identification by LC/TOF-MS is accomplished with the accurate mass (and the subsequent generated empirical formula) of the protonated molecules [M + H]+, along with the accurate mass of the main fragment ion and the characteristic chlorine isotope cluster present in all of them. Accurate mass measurements are highly useful in this type of complex sample analyses since they allow us to achieve a high degree of specificity, often needed when other interferents are present in the matrix. The mass accuracy typically obtained is routinely better than 2 ppm. The sensitivity, linearity, precision, mass accuracy, and matrix effects are studied as well, illustrating the potential of this technique for routine quantitative analyses of herbicides in olive oil. Limits of detection (LODs) range from 1 to 5 microg/kg, which are far below the required maximum residue level (MRL) of 100 microg/kg for these herbicides in olive oil.

Atrazine↗

PubMed2005

Multi-residue pesticide analysis in fruits and vegetables by liquid chromatography-time-of-flight mass spectrometry.

In this work, a new multi-residue methodology using liquid chromatography-time-of-flight mass spectrometry (LC-TOF-MS) for the quantitative (routine) analysis of 15 pesticide residues has been developed. The analytical performance of the method was evaluated for different types of fruit and vegetables: pepper, broccoli, tomato, orange, lemon, apple and melon. The accurate mass measurements were compared in different matrices at significantly different concentration levels (from 0.01 to 0.5 mg/kg) obtaining accuracy errors lower than 2 ppm, which is well within the accepted limits for elemental confirmation. Linearity of response over two orders of magnitude was demonstrated (r > 0.99). Matrix effects resulting in suppression or enhancement of the response were frequently observed, most notably in broccoli and citrus. Instrumental limits of detection (LOD) were between 0.0005 and 0.03 mg/kg depending on the commodity and pesticide studied, all being within European Union regulations for food monitoring program. Finally, the methodology was applied to the analysis of two samples from an inter-laboratory exercise. The high degree of confirmation for target pesticides by accurate mass measurements demonstrated the applicability of the method in routine analysis. This study is a valuable indicator of the potential of LC-TOF-MS for quantitative multi-residue analysis of pesticides in vegetables and fruits.

Chromatography, Liquid↗

PubMed2005

Discovering metabolites of post-harvest fungicides in citrus with liquid chromatography/time-of-flight mass spectrometry and ion trap tandem mass spectrometry.

In this study, we benefit from the combination of liquid chromatography (LC)/time-of-flight (TOF) MS accurate mass measurements to generate elemental compositions of ions and LC/ion trap multiple MS (MSn) providing complementary structural information, which is useful for the elucidation of unknown organic compounds at trace levels in complex food extracts. We have applied this approach to investigate different citrus fruits extracts, and we have identified two post-harvest fungicides (imazalil and prochloraz), the main degradation product of imazalil ([M + H]+, m/z 257) and a non-previously reported prochloraz degradation product ([M + H]+, m/z 282). The database-mediated identification of the parent compounds was based on the generated elemental composition obtained from accurate mass measurements and additional qualitative information from the high resolution chlorine isotopic clusters of both the protonated molecules (imazalil, [M + H]+ 297.0556, <0.1 ppm error, 2-Cl; prochloraz, [M + H]+ 376.0381, 1.9 ppm error, 3-Cl) and their characteristic fragments ions (imazalil: m/z 255 and 159; prochloraz: m/z 308 and 266). The correlation between the structural information provided by ion trap MS/MS fragmentation pathways of the parent species and the TOF accurate mass elemental composition data of the degradation products were the key to elucidate the structures of the degradation products of both post-harvest fungicides. Finally, where standards were not available (prochloraz), further confirmation was obtained by synthesizing the proposed degradation product by acid hydrolysis of the parent standard and confirmation by LC/TOF-MS.

Chromatography, Liquid↗

PubMed2005

Determination of pesticide residues in olives and olive oil by matrix solid-phase dispersion followed by gas chromatography/mass spectrometry and liquid chromatography/tandem mass spectrometry.

A novel analytical approach has been developed and evaluated for the quantitative analysis of a selected group of widely used pesticides (dimethoate, simazine, atrazine, diuron, terbuthylazine, methyl-parathion, methyl-pirimiphos, endosulfan I, endosulfan II, endosulfan sulphate, cypermethrin and deltamethrin), which can be found at trace levels in olive oil and olives. The proposed methodology is based on matrix solid-phase dispersion (MSPD), (with a preliminary liquid-liquid extraction in olive oil samples) using aminopropyl as sorbent material with a clean-up performed in the elution step with Florisil, followed by mass spectrometric identification and quantitation of the selected pesticides using both gas chromatography-mass spectrometry (GC-MS) in selected ion monitoring (SIM) mode and liquid chromatography tandem mass spectrometry (LC-MS-MS) in positive ionization mode. The recoveries obtained (with mean values between 85 and 115% (obtained at different fortification levels) with RSD values below 10% in most cases, confirm the usefulness of the proposed methodology for the analyses of these kind of complex samples with a high fat content. Moreover, the obtained detection limits, which were below 5 microg kg(-1) by LC-MS analyses and ranged from 10 to 60 microg kg(-1) by GC-MS meet the requirements established by the olive oil pesticide regulatory programs. The method was satisfactorily applied to different olives and olive oil samples.

Dimethoate↗

PubMed2005

Searching for non-target chlorinated pesticides in food by liquid chromatography/time-of-flight mass spectrometry.

In this study the unique and most salient features of liquid chromatography/time-of-flight-mass spectrometry (LC/TOFMS) were applied for the identification of non-target chlorinated pesticides in complex food extracts 'a priori', i.e., without the use of standards. The combination of high sensitivity full-scan spectra incorporating accurate mass measurements (routinely better than 2 ppm accuracy) of the protonated molecules with the evidence from resolved isotopic clusters provides the ability to obtain a reduced number of possible elemental compositions (typically 1-2). Databases were then used to find the identity of the suspected species using the elemental composition as a searching criterion. The accurate mass and the generated elemental composition of characteristic fragment ions of the suspected species provide further evidence for the proposed species. With this approach we have identified the following chlorinated pesticides in different market-purchased fruit and vegetable extracts: Chlorotoluron (tomato), iprodione (apple), and procymidone (grapes). Finally, the confirmation and quantitation of these suspected species were successfully accomplished with standards. Other unknown compounds could be partially identified based on the data obtained within this study. As an example, a chlorinated species ('m/z 311') is discussed; the elemental composition and possible structures were proposed and the analytical potential, advantages and disadvantages of the proposed approach critically discussed.

Algorithms↗

PubMedDate not supplied

Flow-through fluorescence-based optosensor with on-line solid-phase separation for the simultaneous determination of a ternary pesticide mixture.

A rapid and selective method was developed for the simultaneous determination of 3 widely used pesticides, carbendazim (CBZ), carbofuran (CF), and benomyl (BNM). The method utilized a single continuous-flow, solid surface fluorometric multioptosensor implemented with a previous separation of the analytes on a minicolumn, placed just before the sensor, that was packed with the same solid support (C18 silica gel) as the flow-through cell. The separation was achieved because of the different kinetics of retention/elution of the pesticides on the solid support in the minicolumn, enabling the sequential arrival of the analytes at the sensing zone. With a single injection of the mixture, 2 of them were more strongly retained in the minicolumn (CF and BNM) while the other (CBZ) passed through the system towards the sensing material where it developed its fluorescence transitory signal. Then, CF and BNM were successively eluted from the solid support using 2 different eluting solutions, and they sequentially reached the sensing zone and developed their respective signals. A multiwavelength fluorescence detection mode was used, recording the signals of each pesticide at its maximum excitation/emission wavelength; therefore, the sensitivity was increased. The system was calibrated using a sample volume of 2000 microL. The linear dynamic range was 80-1400, 250-2400, and 150-2000 ng/mL with detection limits of 15, 68, and 35 ng/mL and relative standard deviation values of 3.5, 3.2, and 2.4% for CBZ, CF, and BNM, respectively. A recovery study was applied to spiked environmental water samples, and recoveries ranged from 96 to 104%.

Air Pollutants, Occupational↗