Determination of pesticide residues in peaches by using gas chromatography and mass spectrometric detection

ABSTRACT

A multi-residue method using selected ion monitoring mode GC-MSD has been developed for the quantitative analysis of 30 widely used pesticides in fresh peaches produced in Swat Malakand, Pakistan. The planned methodology involved a sample extraction procedure using liquid-liquid partition with acetonitrile followed by a clean-up step based on solid-phase extraction (SPE). Method validation was performed in accordance with European Union guidelines. The European Union criteria (recovery 70–120%, RSD <20%) were met for majority of pesticides. For most of the pesticides, signal-to-noise ratios were good and background-corrected mass spectra often contained sufficient diagnostic to enable identity and confirmation. The limits of quantification (LOQs) were in the range 0.01–1.0 mg/kg. The above method was successfully applied to the analysis of peach samples (n = 30) from the field. Pesticide concentration in real peach samples was compared with the maximum residue levels (MRLs). Pesticide residues were detected in 73% of the peach samples. Most frequent residues were metalaxyl, α-cypermethrin, azoxystrobin, dimethoate, tebuconazol, λ-cyhalothrin and spiromesifin in peach samples.     

Arsenic speciation and other parameters of surface and ground water samples of Jamshoro,Pakistan

This study evaluated and interpreted complex data sets of water samples collected from different sampling origins of ground water (hand pump and tube well) and surface water (municipal, river and canal). The aim was to provide information concerning the apportionment of pollution sources to obtain better information about water quality and possible distribution of As with respect to its speciation. The As (III) formed complex with ammonium pyrrolidinedithiocarbamate (APDC) and extracted by surfactant-rich phases in the non-ionic surfactant Triton X-114, while total iAs in water samples was adsorbed on titanium dioxide (TiO₂) and determined by electrothermal atomic absorption spectrometry. The accuracy of the proposed methodologies was confirmed by standard addition method. The recoveries of As (III) and total inorganic arsenic (iAs) were found to be >98%. The results revealed that the ground water of the area under study was more contaminated as compared to surface water samples. The mean concentration of As (III) and As (V) in the surface water samples was found to be 15.8 and 6.00?µg?L^?1, respectively, whereas, in the case of ground water samples, the contents of As (III) and As (V) ranged from 6.20 to 51.0 and 6.40 to 53.0?µg?L^?1, respectively. Principal component analysis performed on a combined (tube well and hand pump) samples data set extracted two significant factors explaining more than 60% of total variance, which suggested that the contamination sources might be natural or anthropogenic.     

Preparation and characterization of crack-free sol–gel based SiO2–TiO2 hybrid nanoparticle film

Owing to the diverse potential applications of hybrid silica–titania thin films, the synthesis and characterization of these films have been carried out with a special focus on application as a medium index layer for multilayered functional coatings. For synthesis, tetraethylorthosilicate and titanium tetraisopropoxide were chosen as precursors for the formation of silica-titania hybrid thin films/nano-composites through an in situ sol–gel process. These films were sequentially obtained on Cu substrate utilizing spin coating. The hybrids were characterized by field emission scanning electron microscope, energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction, atomic force microscopy and Fourier transform infrared spectroscopy (FTIR). Field emission scanning electron microscope morphology displayed a smooth, densified and crack- free layer of silica-titania hybrid nanoparticles in the range of 20–71 nm after calcinations at low temperature of 300ºC for 1 h. X-ray diffraction pattern confirms the phases of titania with higher crystallinity and phase transformation at low temperature. The prepared films were uniform with low 8.852 nm RMS value. The stoichiometry of films was confirmed by EDX results. The FTIR spectroscopy indicated the establishment of heterogeneous chemical bonding between the Ti and Si surfaces through oxygen.     

Aqueous Urea Solution Promoted Resolution of Five-Component Mixture of Amino Acids on Silica TLC Plates

JPC – Journal of Planar Chromatography – Modern TLC - A thin-layer chromatographic system comprising of silica gel as stationary phase and 1.0% aqueous urea solution as mobile phase (pH...     

Bis(2-benzyl-1H-benz­imidazole-N3)dichorozinc(II)

In the title compound, [ZnCl₂(C₁₄H₁₂N₂)₂], the environment around the Zn atom is distorted tetrahedral formed by two Cl atoms and two tertiary N atoms of the 2-benzyl-1H-benz­imidazole ligands. N—H⃛Cl intermolecular hydrogen bonds link the mol­ecules into infinite chains in the [101] direction.     

Methyl (SR)‐10‐chloro‐1,2,3,4,5,6‐hexahydro‐6‐hydroxy‐8‐methoxy‐1‐methyl‐1,9‐phenanthroline‐6‐carboxylate

In the title compound, C₁₆H₁₉ClN₂O₄, the pyridine ring is nearly planar, the piperidine ring is non‐planar and the cyclo­hexane ring adopts a screw‐boat conformation. The carboxyl­ate group makes a dihedral angle of 80.9 (2)° with the least‐squares plane through the cyclo­hexane ring.     

Production of High Purity Multi-Walled Carbon Nanotubes from Catalytic Decomposition of Methane

Acid-based purification process of multi-walled carbon nanotubes (MWNTs) produced via catalytic decomposition of methane with NiO/TiO2 as a catalyst is described. By combining the oxidation in air and the acid refluxes, the impurities, such as amorphous carbon, carbon nanoparticles, and the NiO/TiO2 catalyst, are eliminated. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images confirm the removal of the impurities. The percentage of the carbon nanotubes purity was analyzed using thermal gravimetric analysis (TGA). Using this process, 99.9 wt% purity of MWNTs was obtained.     

'Heat-treatment aqueous two phase system' for purification of serine protease from Kesinai (Streblus asper) leaves

A 'Heat treatment aqueous two phase system' was employed for the first time to purify serine protease from kesinai (Streblus asper) leaves. In this study, introduction of heat treatment procedure in serine protease purification was investigated. In addition, the effects of different molecular weights of polyethylene glycol (PEG 4000, 6000 and 8000) at concentrations of 8, 16 and 21% (w/w) as well as salts (Na-citrate, MgSO? and K?HPO?) at concentrations of 12, 15, 18% (w/w) on serine protease partition behavior were studied. Optimum conditions for serine protease purification were achieved in the PEG-rich phase with composition of 16% PEG6000-15% MgSO?. Also, thermal treatment of kesinai leaves at 55 °C for 15 min resulted in higher purity and recovery yield compared to the non-heat treatment sample. Furthermore, this study investigated the effects of various concentrations of NaCl addition (2, 4, 6 and 8% w/w) and different pH (4, 7 and 9) on the optimization of the system to obtain high yields of the enzyme. The recovery of serine protease was significantly enhanced in the presence of 4% (w/w) of NaCl at pH 7.0. Based on this system, the purification factor was increased 14.4 fold and achieved a high yield of 96.7%.     

Optimization of an efficient semi-solid culture protocol for sterilization and plant regeneration of Centella asiatica (L.) as a medicinal herb

The present study investigates the effects of different concentrations, as well as type of plant growth regulators (PGRs) and medium (MS, Duchefa) on the growth and development of Centella asiatica in semi-solid culture. In addition, a protocol for successful sterilization of C.asiatica explants prepared from field-grown plants highly exposed to fungal and bacterial contamination was determined. Results for sterilization treatments revealed that applying HgCl? and Plant Preservative Mixture (PPM) with cetrimide, bavistin and trimethoprim which were included after washing with tap water, followed by the addition of PPM in the medium, produced a very satisfactory result (clean culture 90 ± 1.33%) and TS5 (decon + cetrimide 1% + bavistin 150 mg/L + trimethoprim 50 mg/L + HgCl?0.1% + PPM 2% soak and 2 mL/L in medium) was hence chosen as the best method of sterilization for C.asiatica. The synergistic combination of 6 benzylaminopurine (BAP) and 1-naphthaleneacetic acid (NAA) in concentrations of 2 mg/L and 0.1 mg/L, respectively, in Duchefa medium compared with MS induced the most optimal percentage of sprouted shoots (93 ± 0.667), number of shoots (5.2 ± 0.079) and nodes (4 ± 0.067) per explant, leaf per explant (14 ± 0.107) and shoot length (4.1 ± 0.67 cm). Furthermore, optimum rooting frequency (95.2 ± 0.81%), the number of roots/shoot (7.5 ± 0.107) and the mean root length (4.5 ± 0.133 cm) occurred for shoots that were cultured on full-strength MS medium containing 0.5 mg/L indole-3-butyric acid (IBA). In this study, the acclimatized plantlets were successfully established with almost 85% survival. The findings of this study have proven an efficient medium and PGR concentration for the mass propagation of C.asiatica. These findings would be useful in micropropagation and ex situ conservation of this plant.