On-line preconcentration strategies for analyzing pesticides in fruits and vegetables by micellar electrokinetic chromatography

Five pesticides (fludioxonil, procymidone, pyriproxyfen, dinoseb and carbendazim) were separated in reversed migration micellar electrokinetic chromatography (RM-MEKC) using 20 mmol l(-1) phosphate buffer at pH 2.3, containing 25 mmol l(-1) sodium dodecylsulfate and 10% methanol. Three on-line concentration strategies, sweeping (SW), normal stacking with reversed migration and a water plug (SRW) and stacking with reverse migration and removal of sample matrix using polarity switching (SRMM), were compared. About 10-, 30- and 50-fold increases in detection sensitivity, compared with standard hydrodynamic injection (5 s at 0.5 psi), were observed with SW, SRW and SRMM, respectively. Limits of detection (LODs) ranged from 0.002 to 0.03 microg ml(-1) using only the on-line preconcentration procedures without any off-line concentration of the extract. A solid-phase extraction (SPE) procedure, for previous isolation and concentration of the analytes, was used in combination with any of the proposed on-line preconcentration strategies, which achieves the determination of pesticides at limits of quantification (LOQs) lower than 0.01 mg kg(-1). The recoveries obtained by SPE in samples spiked at 0.01 mg kg(-1) were between 70 and 100%, with RSDs between 10 and 18% using SRMM. Samples of fruits and vegetables were taken from the market, extracted by the proposed procedure and analyzed with RM-MEKC with the on-line strategies.     

Matrix solid-phase dispersion extraction of organophosphorus pesticides from propolis extracts and recovery evaluation by GC/MS

Five organophosphorus pesticides (dichlorvos, diazinon, malathion, methyl parathion and coumaphos) were extracted from propolis by matrix solid-phase dispersion (MSPD) extraction using octadecylsilica (C18, 1.0 g) as dispersant material. The kind of solvent elution (acetonitrile or ethyl acetate), volume (8 mL and 15 mL), and adsorbent used to clean-up the extracts (graphitized carbon, florisil™ and silica) were optimized using fortified propolis samples (5.0 μg g⁻¹). Recovery was determined by gas chromatography with mass spectrometric detection in selected ion monitoring mode (GC/MS-SIM) and statistical analysis was done to determine better extraction conditions. Relatively high recovery and lower relative standard deviation values (3.1–14.6%) were obtained when analytes were eluted with ethyl acetate from the MSPD column. Diazinon, malathion, methyl parathion, and coumaphos show recoveries of 72.7%, 84.6%, 62.6%, and 78.3%, respectively. In contrast, the recovery for dichlorvos was 53.8%. Additional adsorbents tested for clean-up and increase in solvent elution did not affect recoveries positively and caused a high background in chromatograms. Thus, final conditions were 1 mL of sample, 1 g C18 and 8 mL of ethyl acetate.     

The peroxidase/H2O2 system as a free radical-generating agent for gelling maize bran arabinoxylans: rheological and structural properties

The oxidative gelation of maize bran arabinoxylans (MBAX) using a peroxidase/H(2)O(2) system as a free radical-generating agent was investigated. The peroxidase/H(2)O(2) system led to the formation of dimers and trimer of ferulic acid as covalent cross-link structures in the MBAX network. MBAX gels at 4% (w/v) presented a storage modulus of 180 Pa. The structural parameters of MBAX gels were calculated from swelling experiments. MBAX gels presented a molecular weight between two cross-links (Mc), a cross-linking density (ρ(c)) and a mesh size (x) of 49 × 103 g/mol, 30 × 10-6 mol/cm3 and 193 nm, respectively.     

Urban Elementary STEM Initiative

The new standards for K–12 science education suggest that student learning should be more integrated and should focus on crosscutting concepts and core ideas from the areas of physical science, life science, Earth/space science, and engineering/technology. This paper describes large‐scale, urban elementary‐focused science, technology, engineering, and mathematics (STEM) collaboration between a large urban school district, various STEM‐focused community stakeholders, and a research‐focused private university. The collaboration includes the development of an integrated STEM curriculum for grade K–5 with accompanying teacher professional development. This mixed‐methodology study describes findings from focus group interviews and a survey of teachers from Title I elementary schools. Findings suggest the importance of the following critical features of professional development: (a) coherence, (b) content focus, (c) active learning, (d) collective participation, and (e) duration to the success of large‐scale STEM urban elementary school reform     

Synthesis of complexes with the polydentate ligand N,N′-bis(2-hydroxyphenyl)-pyridine-2,6-dicarboxamide

The pentadentate ligand N,N′-bis(2-hydroxyphenyl)-pyridine-2,6-dicarboxamide (POPYH₄) has been used to prepare a variety of new complexes [HNEt₃]₂[Zn₄Cl(POPYH)₃] (2), [HNEt₃][PdCl(POPYH₂)] (3), [HNEt₃][Ni(POPYH)] (4) and K[Ni(POPYH)] (5) which show the versatility of this multidentate ligand. The complexes have been characterised spectroscopically and their molecular and crystal structures have been determined by single crystal X-ray diffraction techniques. In these complexes the ligand exhibits different modes of coordination towards different transition metal ions. The structure of triethylammonium salt of the Zn(II) dianion 2 consists of an unusual tetra-zinc core supported by three POPYH ligands each one of which links two adjacent zinc centres through two oxygen and two nitrogen donor atoms. The salt of the square planar Pd(II) anion 3 contains one POPYH₂ ligand which coordinates in a tridentate fashion through the two deprotonated amido groups and by the central pyridine nitrogen donor. The two Ni(II) salts 4 and 5 contain the same [Ni(POPYH)]⁻ anion in which the square planar Ni(II) centre is chelated by a POPYH ligand through the two deprotonated amido nitrogen atoms, the pyridine nitrogen and a deprotonated hydroxyl group.