Maria Fernandez-Alvarez

Simultaneous determination of traces of pyrethroids, organochlorines and other main plant protection agents in agricultural soils by headspace solid-phase microextraction–gas chromatography

A solvent-free and simple method based on headspace solid-phase microextraction (HS-SPME) was developed in order to determine simultaneously 36 common pesticides and breakdown products (mostly pyrethroids and organochlorine compounds) in soil. The analysis was carried out by gas chromatography with micro-electron-capture detection (GC-microECD). As far as we know, this is the first study about the SPME of pyrethroid insecticides from soil. Factors such as extraction temperature, matrix modification by addition of water, salt addition (% NaCl) and fiber coating were considered in the optimization of the HS-SPME. To this end, a 3 x 2(3-1) fractional factorial design was performed. The results showed that temperature and fiber coating were the most significant variables affecting extraction efficiency. A suitable sensitivity for all investigated compounds was achieved at 100 degrees C by extracting soil samples wetted with 0.5 mL of ultrapure water (0% NaCl) employing a polyacrylate (PA) coating fiber. Using the recommended extraction conditions with GC-microECD, a linear calibration could be achieved over a range of two orders of magnitude for both groups of analytes. Limits of detection (LODS) at the sub-ng g(-1) level were attained and relative standard deviations (RSDs) were found to be lower than 14% for both groups of pesticides. Matrix effects were investigated by the analysis of different soil samples fortified with the target compounds. The method accuracy was assessed and good recovery values (>70%, in most cases) were obtained. The method was also validated with a certified reference material (RTC-CRM818-050), which was quantified using a standard addition protocol. Finally, the proposed HS-SPME-GC-microECD methodology was further applied to the screening of environmental soil samples for the presence of the target pesticides.

Development of a solid-phase microextraction gas chromatography with microelectron-capture detection method for a multiresidue analysis of pesticides in bovine milk

A simple and rapid method based on solid-phase microextraction (SPME) technique followed by gas chromatography with microelectron-capture detection (GC-microECD) was developed for the simultaneous determination of more than 30 pesticides (pyrethroids and organochlorinated among others) in milk. To our knowledge, this is the first application of SPME for the determination of pyrethroid pesticides in milk. Negative matrix effects due to the complexity and lipophility of the studied matrix were reduced by diluting the sample with distilled water. A 2(5-1) fractional factorial design was performed to assess the influence of several factors (type of fiber coating, sampling mode, stirring, extraction temperature, and addition of sodium chloride) on the SPME procedure and to determine the optimal extraction conditions. After optimization of all the significant variables and interactions, the recommended procedure was established as follows: DSPME (using a polydimethylsiloxane (PDMS)/divinylbenzene (DVB) coating) of 1 mL of milk sample diluted with Milli-Q water (1:10 dilution ratio), at 100 degrees C, under stirring for 30 min. The proposed method showed good linearity and high sensitivity, with limits of detection (LOD) at the sub-ng mL(-1) level. Within a day and among days precisions were also evaluated (R.S.D.<15%). One of the most important attainments of this work was the use of external calibration with milk-matched standards to quantify the levels of the target analytes. The method was tested with liquid and powdered milk samples with different fat contents covering the whole commercial range. The efficiency of the extraction process was studied at several analyte concentration levels obtaining high recoveries (>80% in most cases) for different types of full-fat milks. The optimized procedure was validated with powdered milk certified reference material, which was quantified using external calibration and standard addition protocols. Finally, the DSPME-GC-microECD methodology was applied to the analysis of milk samples collected in farms of dairy cattle from NW Spain.

Development of a matrix solid-phase dispersion method for the simultaneous determination of pyrethroid and organochlorinated pesticides in cattle feed.

A matrix solid-phase dispersion (MSPD) method was developed for the simultaneous extraction of 36 common pesticides and breakdown products (mostly pyrethroids and organochlorines) in cattle feed. Different parameters affecting the extraction efficiency (such as dispersing phase, clean-up adsorbent and elution volume) were investigated. The experimental procedure was optimized using a multivariate statistical approach and the final analyses were carried out by GC-muECD. Several protocols for extract purification were also studied. As far as we know, this is the first application of MSPD for the extraction of most of the target pesticides from animal feed. Using the optimized extraction conditions, the method was validated in terms of accuracy, and precision (within-a-day and among-days), using a certified reference material (CRM 115) as well as spiked cattle feedingstuffs at different concentration levels. A matrix effect study was also carried out using various real samples. The recoveries were satisfactory (>75% in most cases) and the quantification limits, at the sub-ngg(-1) or low-ngg(-1) level, complied with the regulated maximum residue levels (MRLs) in animal feed and in main crops used in the preparation of cattle feeding materials. Finally, the MSPD-GC-muECD methodology was applied to the analysis of real cattle feed samples collected in farms of dairy cattle from NW Spain.

Development of a solid-phase microextraction gas chromatography with microelectron-capture detection method for the determination of 5-bromo-5-nitro-1,3-dioxane in rinse-off cosmetics

5-Bromo-5-nitro-1,3-dioxane (bronidox) is a bromine-containing preservative often used in rinse-off cosmetics but also subjected to several restrictions according to the European Cosmetic Products Regulation. Thus, as a part of a quality control procedure, analytical methods for the determination of this compound in different types of cosmetics are required. In the present work, a solvent-free and simple methodology based on solid-phase microextraction (SPME) followed by gas chromatography with microelectron capture detection (GC-μECD) has been developed and validated for the determination of bronidox in cosmetic samples such as shampoos, body cleansers or facial exfoliants. As far as we know, this is the first application of SPME to this preservative. Negative matrix effects due to the complexity of the studied samples were reduced by dilution with ultrapure water. The influence of several factors on the SPME procedure such as fiber coating, extraction temperature, salt addition (NaCl) and sampling mode has been assessed by performing a 2(4)-factorial design. After optimization, the recommended procedure was established as follows: direct solid-phase microextraction (DSPME), using a PDMS/DVB coating, of 10 mL of diluted cosmetic with 20% NaCl, at room temperature, under stirring for 30 min. Using these suggested extraction conditions, linear calibration could be achieved, with limits of detection (LOD) and quantification (LOQ) well below the maximum authorized concentration (0.1%) established by the European legislation. Relative standard deviations (RSD) lower than 10% were obtained for both within a day and among days precision. The method was applied to diverse types of formulations spiked with bronidox at different concentration levels (0.008-0.10%); these samples were quantified by external calibration and satisfactory recoveries (≥ 70%) were obtained in all cases. Finally, the SPME-GC-μECD methodology was applied to the analysis of several cosmetics labeled or not as containing bronidox. The presence of this preservative in some of these samples was confirmed by GC-MS.

Photo-solid-phase microextraction of selected indoor air pollutants from office buildings. Identification of their photolysis intermediates.

Photo-solid-phase microextraction (photo-SPME) has been employed to study the photolysis of three common indoor air pollutants: coumarin, butylated hydroxytoluene, 2,6-diisopropylnaphthalene. Analytes were first extracted by SPME, and the fibre was subsequently exposed to an irradiation source (i.e. xenon arc or low-pressure mercury lamp) for the selected time (from 2 to 120 min). Analyses of the irradiated fibres were carried out by gas chromatography-mass spectrometry (GC-MS) detection. Photodecay kinetics exhibited a first-order behaviour and their rate constants and half-life times were estimated. Twenty-five photoproducts have been tentatively identified by means of their mass spectra. On the basis of the identified transformation compounds, some photodegradation pathways were proposed. The photoformation-photodecay kinetics of the identified by-products were also monitored by photo-SPME. To the best of our knowledge, photolytic routes for coumarin, butylated hydroxytoluene and 2,6-diisopropylnaphthalene have not been previously investigated.

Simultaneous Extraction and Cleanup Method Based on Pressurized Solvent Extraction for Multiresidue Analysis of Pesticides in Complex Feed Samples

The development of a multiresidue method based on pressurized solvent extraction (PSE) to determine a large number of pesticides (mostly pyrethroids and organochlorines) in cattle feed is described. As far as we know, this is the first work dedicated to the PSE of many of the target pesticides from animal feed. A mixed level fraction design was performed to investigate the influence of several operational variables on the PSE procedure; integrated cleanup strategies were also assessed allowing the direct chromatographic analysis of the extracts. Method accuracy was evaluated by the analysis of a certified reference material (BCR-115) and different fortified cattle feed samples. Most analytes were recovered in the range of 70-110%, with relative standard deviations generally lower than 15%. Limits of detection (LODs) were below the maximum residue levels (MRLs) set by the European Union for animal feed and main crops used in the preparation of feedingstuffs. The applicability of the proposed method was demonstrated by the analysis of real cattle feed samples collected from 23 dairy farms located in Galicia (NW Spain).

Study of the presence of priority pesticides in surface water of river basins located in two areas of intensive dairy farming in the NW Spain (Galicia)

This study provides data about the monitoring over two years of 54 target pesticides in surface water of two river catchments located in two areas of the most intensive dairy farms of Galicia (NW Spain). Solid phase extraction of water samples followed by multi-residue analysis on a triple quadrupole mass spectrometer instrument coupled to liquid chromatography (LC-MS/MS) enabled to acquire the results. The most frequently detected pesticides were acetochlor, alachlor, atrazine and terbuthylazine, as well as some of their metabolites. The concentration profiles of these four substances show a seasonal variation, the highest concentrations corresponding to the period of maize sowing and the application of herbicides. Of the seven priority pesticides evaluated, only alachlor and atrazine were detected. Their follow-up revealed that the concentration thresholds laid down by the EQS for these substances were never exceeded. The sum of the concentrations of the most detected compounds reached a maximum slightl...

Monitoring of pesticide residues in dairy cattle farms from NW Spain.

The consequences of the use of pesticides in agricultural activities for food and feed product safety are subjects of major concern. In the present work, simple and environmentally friendly methodologies were applied to the analysis of soil and cattle feed samples collected in dairy cattle farms from Galicia (NW Spain). This forms part of an integrated study aiming to investigate the global impact of the use of pesticides in such farms. The target compounds were 36 plant protection products belonging to different families. Organochlorine and organophosphorus pesticides were the most commonly detected compounds in the analyzed samples; pyrethroid and chloroacetanilide pesticides were also found in some of them, but not so frequently. Detected levels were rarely above the established legal limits.

Investigation of the photochemical behaviour of pyrethroids lacking the cyclopropane ring by photo‐solid‐phase microextraction and gas chromatography/mass spectrometry

The characterization of by-products arising from the UV photodegradation of two insecticide pyrethroids lacking the cyclopropane ring (flucythrinate and fenvalerate) has been investigated by gas chromatography coupled with mass spectrometry (GC/MS). Twenty photoproducts were tentatively identified mainly based on the interpretation of the experimental mass spectra or by using reference mass spectra. Some of these compounds had not previously been detected. Furthermore, the generation of some of the photoproducts might be a matter for concern due to their potential toxicity. The corresponding photodegradation routes, including postulation of the intermediate radicals, have also been proposed. These photodegradation studies were performed by photo-solid-phase microextraction (photo-SPME) in which the SPME fibre was exposed to light after extraction of the target analytes from aqueous solutions. The degradation kinetics of the investigated pyrethroids and the photoformation-photodegradation curves of the photoproducts generated in situ were also monitored through the ion chromatograms obtained for different irradiation times and the corresponding mass spectra.