Control of pesticide residues by liquid chromatography-mass spectrometry to ensure food safety

Liquid chromatography-mass spectrometry (LC-MS) has become an invaluable technique for the control of pesticide residues to ensure food safety. After an introduction about the regulations that highlights its importance to meet the official requirements on analytical performance, the different mass spectrometers used in this field of research, as well as the LC-MS interfaces and the difficulties associated with quantitative LC-MS determination, are discussed. The ability to use practical data for quantifying pesticides together with the option of obtaining structural information to identify target and non-target parent compounds and metabolites are discussed. Special attention is paid to the impact of sample preparation and chromatography on the ionization efficiency of pesticides from food. The last section is devoted to applications from a food safety point of view. (c) 2006 Wiley Periodicals, Inc.     

Study on the interaction of diarylbutadiynes with free radicals: Interaction with propagating radicals of some vinyl monomers

In order to study the nature of interaction of arylbutadiynes with transient free radicals, polymerization and copolymerization of some vinyl monomers such as methyl methacrylate (MMA), styrene (ST), methacrylonitrile (MAN), vinylidene chloride (VCl₂), ethyl acrylate (EA) and acrylonitrile (AN), were carried out in the presence of diphenylbutadiyne (DPB), 4,4'-butadiynylene-N,N,N',N'-tetra-n-butyl-dibenzamide (BBA), and 4,4'-dibromodiphenylbutadiyne (BPB). MMA gave an intense ESR signal at the polymerization temperature when the polymerization system became viscous, and the number of radicals increased with polymerization time. Strong signals of polyEA and polyMAN radicals were also observed in the presence of DPB when the polymerization system became almost solid. This is a unique case where active transient propagating radicals such as that of polyEA can be detected at polymerization temperature. The rates of polymerization decreased by the presence of the diacetylenes, but the molecular weights did not change with the diacetylene concentrations. UV spectroscopy revealed that there was no diacetylene unit bonded to the obtained polymers, indicating that degradative chain transfer is not the case. The monomer reactivity ratios for MMA-ST and MMA-AN systems did not vary significantly in the presence of the diacetylenes, although some difference was observed. It seems that some arylbutadiynes interact with free radicals but do not form bonds. Received: 4 June 1999/Revised version: 29 September 1999/Accepted: 29 September 1999     

Electrooxidation of DNA at glassy carbon electrodes modified with multiwall carbon nanotubes dispersed in polyethylenimine

This work reports the electrochemical response of the complex between dsDNA and PEI formed in solution and at the surface of glassy carbon electrodes (GCE) modified with a dispersion of multi-walled carbon nanotubes in polyethylenimine (CNT-PEI). Scanning Electron Microscopy and Scanning Electrochemical Microscopy demonstrate that the dispersion covers the whole surface of the electrode although there are areas with higher density of CNT and, consequently, with higher electrochemical reactivity. The adsorption of DNA at GCE/CNT-PEI is fast and it is mainly driven by electrostatic forces. A clear oxidation signal is obtained either for dsDNA or a heterooligonucleotide of 21 bases (oligoY) at potentials smaller than those for the oxidation at bare GCE. The comparison of the behavior of DNA before and after thermal treatment demonstrated that the electrochemical response highly depends on the 3D structure of the nucleic acid.     

Bioavailability of a Heme-Iron Concentrate Product Added to Chocolate Biscuit Filling in Adolescent Girls Living in a Rural Area of Mexico

ABSTRACT: A heme-iron concentrate product derived from swine hemoglobin was used to enrich the chocolate-flavored filling of biscuits and the bioavailability of this source of heme-iron was assessed in adolescent girls. The placebo control (PC) group consisted of 35 teenagers with the highest baseline hemoglobin concentrations. The supplemented groups were randomized to receive biscuits fortified with iron sulfate (IS, n = 37) or heme-iron concentrate (HIC, n = 40). Both groups were supplemented with 10.3 mg Fe/d for 7 wk. Blood chemistry and hematology analyses were performed at baseline and at the end of the study. The baseline prevalence of anemia (hemoglobin <12g/dl) in the entire group was 3.9% and by the end of the study it had fallen to 2.3%. The hemoglobin levels in both supplemented groups increased (P < 0.05) during the study period from 13.6 and 13.5 g/dl for HIC and IS, respectively, at baseline to 14 g/dl at the end of the study. Serum ferritin concentrations decreased by the end of the study in both the PC and IS groups (P < 0.05), but not in the heme group. In conclusion, iron bioavailability from HIC-fortified biscuits was calculated to be 23.7% higher than that observed for IS, as shown by the differences observed in serum ferritin levels during the study. The iron contained in the heme-iron concentrate was well absorbed and tolerated by the adolescents included in the study.     

Temperature and pH‐Sensitive Swelling Behavior of Binary DMAEMA/4VP Grafts on Poly(propylene) Films

Poly(N,N‐dimethylaminoethyl methacrylate) (PDMAEMA) is a polymer or hydrogel that is both thermosensitive and pH sensitive, with a low critical solution temperature (LCST) around 38 °C and a pH critical point of 2.5. Poly(4‐vinylpyridine) (P4VP) shows pH sensitivity with a critical point of 5.1. Grafting of stimuli‐sensitive polymers onto mechanically durable poly(propylene) (PP) substrates was used in this study. We have focused on the influence of temperature and pH on the response of binary graft films produced by gamma irradiation in one and two steps. An LCST‐type hydration transition in the grafts was observed by measuring swelling of the films and water contact angle at different temperatures and pH. An upper critical solution temperature (UCST)‐type behavior was also observed by swelling PP‐g‐DMAEMA and DMAEMA/4VP binary grafting onto PP films at pH 2.2.

     

Dynamic Mechanical Properties of Compatibilized PET with Radiation Oxidized HDPE

Summary Binary blends of HDPE/PET exhibit poor mechanical properties because of their non compatibility. In this work, HDPE was oxidized by gamma-ray preirradiation in air, subsequently heated to destroy peroxides formed by this irradiation and to form polar groups in the HDPE, and then extruded with PET as a compatibilizing method of the blend. The dynamic mechanical properties were studied, and an improvement was observed when the PET content was increased while the HDPE used was irradiated. The largest increase in the mechanical properties was observed for PET contents between 10 and 20% (w/w). The improvement in the dynamic mechanical properties is believed to occur because of a percolation effect of the PET in the HDPE matrix and the radiation-improved compatibility by means of polar groups formed in the polyethylene.     

Trypsin from viscera of vermiculated sailfin catfish, Pterygoplichthys disjunctivus, Weber, 1991: Its purification and characterization

Pterygoplichthys disjunctivus viscera trypsin was purified by fractionation with ammonium sulphate, gel filtration, affinity and ion exchange chromatography (DEAE-Sepharose). Trypsin molecular weight was approximately 27.5 kDa according to SDS–PAGE, shown a single band in zymography. It exhibited maximal activity at pH 9.5 and 40 °C, using N-benzoyl-dl-arginine-p-nitroanilide (BAPNA) as substrate. Enzyme was effectively inhibited by phenyl methyl sulphonyl fluoride (PMSF) (100%), N-α-p-tosyl-l-lysine chloromethyl ketone (TLCK) (85.4%), benzamidine (80.2%), and soybean trypsin inhibitor (75.6%) and partially inhibited by N-tosyl-l-phenylalanine chloromethyl ketone (TPCK) (10.3%), ethylendiaminetetraacetic acid (EDTA) (8.7%) and pepstatin A (1.2%). Enzyme activity was slightly affected by metal ions (Fe²⁺ > Hg²⁺ > Mn²⁺ > K⁺ > Mg²⁺ > Li⁺ > Cu²⁺). Trypsin activity decreased continuously as NaCl concentration increased (0–30%). K_m and k_cat values were 0.13 mM and 1.46 s⁻¹, respectively. Results suggest the enzyme have a potential application where room processing temperatures (25–35 °C) or high salt (30%) concentration are needed, such as in fish sauce production.     

Catalytic effect of monoclinic WO3, hexagonal WO3 and H0.23WO3 on the hydrogen sorption properties of Mg

The H sorption properties of mixtures Mg + WO₃ (having various structures) and Mg + H_0.23WO₃ are reported. First, the higher conversion of Mg into MgH₂ during reactive mechanical grinding (under 1.1 MPa of H₂) for higher WO₃ content is due to the improvement of the milling efficiency. Then, it is shown that the hydrogen absorption properties are almost independent of the crystal structure of the catalyst and that only the particles' size and the specific surface play a major role. Finally, for the desorption process, it appears that the chemical composition and structure of the catalyst, together with the particle size and specific surface have an effect.     

Diacetylene containing polymers

A polyester containing diacetylenic units in main chain was prepared by the polycondensation of m, m-butadiynylene dibenzyl alcohol with terephthaloyl chloride. The polymer was crystalline, and bearly soluble in hot dimethylformamide or dimethylsulfoxide, but insoluble in most organic solvents. It melts at about 200°C. Irradiation of UV light at 75°C gave a reddish brown resin. Heating at temperatures above its melting point gave a shinning black hard solid.     

Functionalization of polypropylene film by radiation grafting of acryloyl chloride and subsequent esterification with Disperse Red 1

Polypropylene (PP) films were grafted with acryloyl chloride by γ‐irradiation, and the grafted films were reacted with an azo dye, Disperse Red 1. The films were characterized by X‐ray diffraction, scanning electron microscopy, atomic force microscopy, and differential scanning calorimetry. It was found that the grafting takes place first on the film surface, and with increase in the radiation dose the grafting penetrated inside of the film, decreasing the crystallinity of the PP film. The surface of the films was homogeneous, and a mesophase was observed for the film grafted with the dye through a polarized optical microscope. The dye underwent trans to cis photoreaction, whereby the red films became colorless by the irradiation of UV light at room temperature, although the color was recovered on standing, and more quickly when heated. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 172–178, 2004