J.C. Moltó

Solid-phase extraction in multi-residue pesticide analysis of water

The determination of pesticides in water is fundamental to the solution of environmental problems as natural waters are usually contaminated with a large number of pesticides. The selection of an isolation and/or concentration technique depends largely on the class of pesticides to be determined. It is often necessary to determine simultaneously a wide variety of compounds in a water sample. Application of solid-phase extraction techniques offers a solution. The mechanisms of solid-phase extraction, types of sorbents and their application to multi-residue pesticide analysis are reviewed.

Pesticide residue determination in fruit and vegetables by liquid chromatography-mass spectrometry

An overview is given of pesticide residue determination in fruit and vegetables by liquid chromatography-mass spectrometry (LC-MS). Emphasis is placed on the thermospray, particle beam and atmospheric pressure ionization interfaces including advantages and drawbacks and typical detection limits. The capacity of each interface to provide useful data for identification/confirmation of analytes and the possibility of obtaining structural information for the identification of target and non-target compounds is discussed. Finally, sample preparation techniques are dealt with in relation to their influence on further LC-MS determination.

Determination of aflatoxins in peanuts by matrix solid-phase dispersion and liquid chromatography ☆

A new method based on matrix solid-phase dispersion (MSPD) extraction was studied to determine aflatoxin B1, B2, G1 and G2 from peanuts. Optimization of different parameters, such as type of solid supports for matrix dispersion and elution solvents were carried out. The method used 2 g of peanut sample, 2 g of C18 bonded silica as MSPD sorbent and acetonitrile as eluting solvent. Recoveries of each aflatoxin spiked to peanut samples at 2.5 ng/g (5 ng/g for aflatoxin G2) level were between 78 and 86% with relative standard deviations ranging from 4 to 7%. The limits of quantification ranged from 0.125 to 2.5 ng/g for the four studied aflatoxins using liquid chromatography (LC) with fluorescence detection. In addition, LC coupled to mass spectrometry with an electrospray interface was used for confirmation of aflatoxins present in real samples. Eleven peanut samples from different countries were analyzed by the proposed method and by using an enzyme-linked immunosorbent assay (ELISA). ELISA test is a good screening method for investigation of these mycotoxins in peanut samples.

Incidence of ochratoxin A in rice and dried fruits from Rabat and Salé area, Morocco

One hundred samples of dried fruits (20 dried raisins, 20 walnuts, 20 peanuts, 20 dried figs and 20 pistachios) and 20 samples of rice purchased from retail shops in the Rabat and Salé area in Morocco were analysed for ochratoxin A (OTA) by immunoaffinity clean-up (IAC) and liquid chromatography (LC) with fluorescence detection. The limit of quantification (LOQ) (S/N = 10:1) of OTA was 0.02 ng g−1 in rice, 0.03 ng g−1 in pistachio, peanut and walnut, and 0.03 ng g−1 in dried raisins and dried figs. The incidences of occurrence of OTA in dried raisins, walnuts, peanuts, dried figs and rice were 30, 35, 25, 65 and 90%, respectively. Analytical results showed that pistachio samples contained no detectable OTA, but concentrations ranged from 0.02 ± 0.01 to 32.4 ± 2.10 ng g−1 in rice, from 0.10 ± 0.05 to 2.36 ± 0.75 in peanut, from 0.03 ± 0.01 to 1.42 ± 0.45 in dried figs, from 0.05 ± 0.02 to 4.95 ± 0.02 in dried raisins, and from 0.04 ± 0.01 to 0.23 ± 0.05 in walnuts. The results also showed that 15% of the total number of rice samples analysed exceeded the 2002 regulatory limit set by European Union regulations for cereals. This is the first report on the occurrence of OTA in dried fruits and rice available in Morocco.

Assessment of the microbiological quality and wash treatments of lettuce served in University restaurants.

One hundred and forty-four samples of lettuce from 16 University restaurants were analyzed. The mesophilic aerobic counts of all samples ranged from 3.01 to 7.81 log10 CFU g(-1). Results of total coliforms ranged from < 0.47 to > 3.38 log10 most probable number (MPN) g(-1). Of the lettuce samples, 25.7% harbored Escherichia coli, 22.9% Staphylococcus aureus and 84% group D streptococci. Similarly, 10.4% of the samples harbored Aeromonas hydrophila, 2.8% Pseudomonas aeruginosa, and coliforms such as 14.6% Citrobacter freundii, 8.3% Klebsiella pneumoniae, 4.2% Enterobacter cloacae and 1.4% Providencia spp. Salmonella, Shigella and E. coli O157:H7 were not detected. When sodium hypochlorite or potassium permanganate solutions were used in washing procedures, the aerobic microorganisms were reduced by more than two log units, and total coliforms by at least one log.

Determination of triazines and organophosphorus pesticides in water samples using solid-phase extraction

Octadecyl (C18)-bonded porous silica was evaluated for the extraction of triazine and organophosphorus pesticides from natural water. The extraction results showed an effective performance when 11 of water was passed through small glass columns containing 500 mg of 50-100-microns C18 bonded porous silica. The adsorbed compounds were removed with ethyl acetate, evaporated to 200 microliters and determined by gas chromatography. The overall average recoveries were greater than 85% except for dimethoate and trichlorfon. Application of this procedure to the analysis of natural water samples gave results that agree well with those obtained by solvent extraction methods.

Matrix effects on solid-phase microextraction of organophosphorus pesticides from water

Abstract This study develops a method for solid-phase microextraction (SPME) of eight organophosphorus pesticides, diazinon, fenthion, fenitrothion (sumithion), methyl-parathion, parathion, methyl-trithion, ethion and triazophos, from water. Determination is carried out by gas chromatography with nitrogen-phosphorus detection. To perform the SPME, poly(dimethylsiloxane) and polyacrylate fibers were initially compared on the basis of their absorption capacities for the selected pesticides, and polyacrylate was selected to accomplish the rest of assays. The main factors affecting the SPME process such as memory effect, stirring rate, extraction temperature and absorption-time profile were studied. The proposed method requires 2 ml of sample and reaches limits of detection ranging between 6 ng/l for fenthion and 136 ng/l for methyl-parathion, with relative standard deviations at the 500 ng/l level between 2% for diazinon and 13% for ethion. The method was applied to spiked tapwater, seawater, wastewater with high dissolved organic matter content (DOC = 212 mg/l) and water containing 15 mg/l of sodium lauryl sulfate (SDS), which were previously analyzed to control interferences. Recoveries for diazinon, fenthion and methyl-trithion were better from seawater than from Milli-Q water. Recoveries for fenthion and ethion increased with the presence of SDS and those for methyl-parathion and triazophos decreased from the wastewater because of the presence of the organic matter. Finally, a wastewater from a pesticide producer industry was analyzed showing the presence of diazinon and ethion at concentrations of 0.97 μg/l and 0.67 μg/l, respectively. Results were in concordance with those obtained using a standard liquid-liquid extraction method.

Solid-phase extraction of quaternary ammonium herbicides.

This paper highlights recent advances in the solid-phase extraction (SPE) of quaternary ammonium herbicides in water, soil, plant and biological samples. After a brief introduction summarizing the properties of quaternary ammonium herbicides and the difficulties involved in measuring them, attention is paid primarily to solid supports used for isolation and concentration, pre-treatments required for the different matrices, and eluents applied for quantitative desorption of these analytes. The determination techniques used after SPE and applications of the proposed SPE methodology are also briefly discussed.

Dietary intake and food pattern among university students

Dietary intake and food pattern were determined among university students. Nine hundred-eighteen students (384 males and 534 females) completed a 24 hour recall and a questionnaire. This study showed an average energy intake of 10.3 and 8.0 MJ among male and female university students. The mean intakes of energy and magnesium for males and energy, iron, magnesium and zinc for females were lower to the Spanish Recommended Intakes. For males, breakfast, lunch, dinner and snacks bring about 18, 33, 25 and 27% of total dairy energy, respectively, however, for females a 15, 34, 23 and 27% of total dairy energy were obtained for breakfast, lunch, dinner and snacks, respectively. The university population consumed a diet with too much proteins and fats as compared to the Spanish recommendations. More attention should be focussed on the energy and nutrient intake for this population according to the recommended values.

Optimization of a matrix solid-phase dispersion method for the analysis of pesticide residues in vegetables

A multiresidue method based on matrix solid-phase dispersion (MSPD) is studied to determine chlorfenvinfos, chlorpyrifos, fenarimol, iprodione, procimydone, propiconazole, tetradifon, triadimefon and vinclozolin in artichokes, green beans, lettuces and tomatoes. Alumina, silica and Florisil were assessed as extracting phases, and the extracts from Florisil were the cleanest. To facilitate manual extraction, sand was added to the sample together with the dispersing phase. Three eluting systems were then studied, and dichloromethane proved to be the best. Further purification can be performed using solid-phase cleanup after diluting extracts with aqueous solutions. Octyl- and octadecyl-silica, modifications of the aqueous diluted extracts and several eluting solvents were studied. Determination was done by capillary gas chromatography (GC) with electron-capture detection, and confirmed by GC-MS using the electron impact mode and the selected ion monitoring. The proposed MSPD method was used to analyze 48 samples taken in the course of a year. Procymidone, vinclozolin, chlorpyrifos and chlorfenvinfos were identified in 10 samples at levels below the maximum residue levels allowed by the Spanish Government.