Application of GC–MSD and LC–MS/MS for the determination of priority pesticides in baby foods in Serbian market

Babies and small children are especially sensitive population to the exposure to environmental contaminants. Their small mass and developing systems, including brain development may show adverse health effects from even low levels of contamination on a chronic or single dose case. In this paper one extraction method and two chromatographic techniques for the determination of pesticide residues in baby food were evaluated. A liquid chromatography–tandem mass spectrometry technique combined with electrospray ionization (ESI), (LC–MS/MS) and gas chromatography–mass spectrometry detection (GC–MSD) technique were applied in the detection of 50 pesticides in baby food. So-called QuEChERS (quick, easy, cheap, effective, rugged and safe) method was used as a sample preparation procedure. The recoveries were investigated at three levels (5, 10 and 50 μg/kg) and the results obtained showed compliance with the contemporary EU requirements with a few exceptions. LOQs for most of the tested pesticides were below the EU MRLs (10 μg/kg), except deltamethrin, cypermethrin, fenvalerate, phosalone and beta-cyfluthrin (LOQs were 10 μg/kg). Both techniques were applied in the analysis of 50 samples of baby food manufactured in Serbia.     

Study on the effect of grain storage and processing on deltamethrin residues in post-harvest treated wheat with regard to baby-food safety requirements

The effects of storage intervals and of milling procedures on dissipation of deltamethrin residues in post-harvest treated wheat grain were studied with the aim to obtain scientific data on compliance of the processed products with the safety requirements concerning baby foods. The insecticide formulation was applied on stored wheat at a recommended rate of active ingredient of 0.5 mg kg^-1 and at a higher rate of 4 mg kg^-1, performing the highest protective effect. The dissipation of residues and their distribution in different fractions of the milled grain were studied after various storage intervals, from 7 to 270 days after treatment. Eight fractions—bran, semolina, three types of groats, and three types of flour—were collected after milling of grain and analysed for determination of pesticide residues. The residues were determined by gas chromatography characterized by the limit of determination of 0.005 mg kg^-1, low enough for enforcement of the maximum residue level of 0.01 mg kg^-1 established by the European Commission Directive for any pesticide in cereal-based foods. Deltamethrin applied post-harvest on wheat as grain protectant was distinguished by low rate of degradation on the grain under practical storage conditions. One hundred and eighty days after treatment at an application rate of 0.5 mg kg^-1, the residues were between 0.03 and 0.2 mg kg^-1 in the various types of flour. Two hundred and seventy days after treatment at a rate of 4 mg kg^-1, the residues in the flour were in the range of 0.4-1.5 mg kg^-1.     

Antimicrobial effects of nanofiber poly(caprolactone) tissue scaffolds releasing rifampicin

This study quantified the antibiotic release kinetics and subsequent bactericidal efficacy of rifampicin (RIF) against Gram-positive and Gram-negative bacteria under in vitro static conditions. Antibiotic-loaded scaffolds were fabricated by electrospinning poly(caprolactone) (PCL) with 10% or 20% (w/w) RIF. Scaffold fiber diameter and RIF loading were characterized, and RIF release kinetics were measured. RIF-releasing and RIF-free scaffolds were inoculated with Pseudomonas aeruginosa and Staphylococcus epidermidis, and the suspended concentration live and dead bacteria were determined by fluorescent microscopy. Adherent bacteria and biofilm formation were examined using scanning electron microscopy. Mean fiber diameters were 557 ± 399 nm for RIF-free, 402 ± 225 nm for 10% RIF, and 665 ± 402 nm for 20% RIF scaffolds. RIF release kinetics exhibited a short-burst release during the first hour, followed by a 7 h, zero-order release during which both RIF scaffolds released ~50% of their initial RIF mass loading. P. aeruginosa and S. epidermidis suspended cell populations proliferated in accordance with logarithmic growth models when exposed to control scaffolds; however both RIF-containing scaffolds completely inhibited bacterial growth in suspension and, subsequently, prevented biofilm formation within the scaffolds through the first 6 h.     

Pesticide residues in apples grown under a conventional and integrated pest management system

This paper describes method validation for determination of more than 40 pesticides in apples using a GC technique. Target compounds belonged to the organochlorine, organophosphorus, carbamates, pyrethroids, triazoles, dicarboximides and strobilurins groups, among others. Sample preparation consisted of acetone extraction and subsequent cleanup/concentration by SPE with a polymer-based sorbent. Single quadrupole GC–MS operating in SIM mode and electron impact ionization was used for identification and quantification of the pesticides. Average recoveries for analytes ranged between 70 and 110% at three fortification levels – 0.01, 0.1 and 0.2 mg kg^?1. Relative standard deviations were lower than 20% for all tested compounds. Calculated limits of detection and limits of quantification were below 0.01 mg kg^?1, which were sufficiently low compared to the maximum residue levels (MRLs) established by European legislation. The proposed method was applied for determination of pesticide residue in four selected apple varieties after harvesting. Whole and processed fruits (peel and peeled fruits) were analyzed from different treatment systems: two conventional, one based on integrated pest management (IPM) and two variants based on organic production (controls). Higher levels of pesticide residues were found in apple fruits under conventional conditions. Fenitrothion and chlorpyrifos residues were detected frequently in apple peel at concentrations up to 0.45 and 0.77 mg kg^?1, respectively. The levels found in the whole fruits of the same samples were much lower than in peel and below the respective MRLs (0.5 mg kg^?1 for both pesticides). Measurable residues of triadimenol only, up to 0.05 mg kg^?1, concentrated in the peel, were found in the apples from IPM.     

Modelling emergence of oscillations in communicating bacteria: a structured approach from one to many cells

Population-level measurements of phenotypic behaviour in biological systems may not necessarily reflect individual cell behaviour. To assess qualitative changes in the behaviour of a single cell, when alone and when part of a community, we developed an agent-based model describing the metabolic states of a population of quorum-coupled cells. The modelling is motivated by published experimental work of a synthetic genetic regulatory network (GRN) used in Escherichia coli cells that exhibit oscillatory behaviour across the population. To decipher the mechanisms underlying oscillations in the system, we investigate the behaviour of the model via numerical simulation and bifurcation analysis. In particular, we study the effect of an increase in population size as well as the spatio-temporal behaviour of the model. Our results demonstrate that oscillations are possible only in the presence of a high concentration of the coupling chemical and are due to a time scale separation in key regulatory components of the system. The model suggests that the population establishes oscillatory behaviour as the system''s preferred stable state. This is achieved via an effective increase in coupling across the population. We conclude that population effects in GRN design need to be taken into consideration and be part of the design process. This is important in planning intervention strategies or designing specific cell behaviours.     

Using immersive virtual reality to remotely examine performance differences between dominant and non-dominant hands

Virtual Reality - Circle drawing may be a useful task to study upper-limb function in patient populations. However, previous studies rely on expensive and bulky robotics to measure performance. For...     

Effects of processing on pesticide residues in peaches intended for baby food

Peaches containing added residues of chlorpyrifos-methyl, fenitrothion, procymidone and vinclozolin were used for simulated industrial processing in the manufacture of baby food puree. Residues were determined in raw material, in intermediate products at crucial steps of the processing procedure and in final products. Determination of residues was performed by an analytical method, distinguished by high sensitivity, based on acetone extraction, a two-step clean-up/pre-concentration on graphitized carbon and SAX/PSA sorbent, and GC-ECD. The results of the study were interpreted with respect to enforcement of the stringent Maximum Residue Limit (MRL) of 0.01 mg kg^-1 established by the European Commission (EC) for any pesticide in baby food. Peeling was identified as the most effective procedure in reducing residues. Thermal treatment (concentration and sterilisation) substantially reduced organophosphate (chlorpyrifos-methyl, fenitrothion) residues, whereas procymidone and vinclozolin residue levels were increased in peach puree.     

RF diode reactive sputtering of n- and p-type zinc oxide thin films

We present the relationship between parameters of reactive RF diode sputtering from a zinc oxide (ZnO) target and the crystalline, electrical and optical properties of n-/p-type ZnO thin films. The properties of the ZnO thin films depended on RF power, substrate temperature and, particularly, on working gas mixtures of Ar/O₂ and of Ar/N₂. Sputtering in Ar+O₂ working gas (up to 75% of O₂) improved the structure of an n-type ZnO thin film, from fibrous ZnO grains to columnar crystallites, both preferentially oriented along the c-axis normally to the substrate (〈0 0 2〉 direction). These films had good piezoelectric properties but also high resistivity (ρ≈10³ Ω cm). ZnO:N p-type films exhibited nanograin structure with preferential 〈0 0 2〉 orientation at 25% N₂ and 〈1 0 0〉 orientation for higher N₂ content. The presence of nitrogen N_O at O-sites forming N_O-O acceptor complexes in ZnO was proven by SIMS and Raman spectroscopy. A minimum value of resistivity of 790 Ω cm, a p-type carrier concentration of 3.6×10¹⁴ cm⁻³ and a Hall mobility of 22 cm² V⁻¹ s⁻¹ were obtained at 75% N₂.     

Characterization of gallium-nitrogen co-doped zinc oxide thin films prepared by RF diode sputtering

We investigated the possibility of achieving p-type zinc oxide (ZnO) by RF diode sputtering and gallium-nitrogen co-doping. ZnO:Ga:N thin films were prepared with a different N₂ content in Ar/N₂ working gas, ranging from 0 to 100%, and at a varying substrate temperature, from room temperature (RT) to 300 °C. A hole conduction with maximum carrier concentration of 2.6 × 10¹⁸ cm⁻³, mobility of 2 cm²/Vs and resistivity of 1.5 Ω cm resulted from deposition at RT with 100% N₂. It arose from N incorporation and formation of N_O acceptors. In the secondary ion mass spectrometry (SIMS) depth profiles of the co-doped films were observed NO/NO₂ negative ions. Average transmittance (including Corning glass substrate) across the visible spectrum varied (60 ÷ 66%) with increasing nitrogen content (50 ÷ 100% N₂). As the substrate temperature increased (RT - 300 °C), highly transparent (T ∼72-83%) and conductive (electron concentrations of 10¹⁷-10¹⁹ cm⁻³) n-type ZnO:Ga:N films were attained. Reduction of optical band gap (E_g) (∼3.13-3.08 eV) was observed for co-doped ZnO films. Atomic force microscopy (AFM) images revealed that the films grown at RT have roughness of approximately 5.3 nm while roughness of those grown at 300 °C is approximately 3.9 nm.