Development and validation of a multiresidue method for the determination of 323 pesticide residues in dry herbs using QuEChERS method and LC-ESI-MS/MS

A multiresidue method was studied for determination of 323 pesticides representing a wide range of physicochemical properties in dry herbs (chamomile and parsley) based on QuEChERS method and LC-ESI-MS/MS analysis. In the current study, three different parameters were optimised for a higher accuracy and a lower matrix effects: extraction procedures, cleanup and matrix effect. Optimum extraction efficiency was obtained at sample hydration of 10 mL water on 2 g dry herbs and soaking time for 10 min. Use of different extraction techniques supported the use of mechanical shaker in comparison with ultrasound and handed shaking. As a way to remove interfering components from final extract, different cleanup techniques were studied: three dispersive solid phase extraction (D-SPE) (C₁₈, primary secondary amine and graphitised carbon black) have been investigated; matrix effect was reduced, but several pesticides were lost during the cleanup process. Unlike the SPE (hydrophilic lipophilic balanced polymer) produced a good recovery with all substances without expected reduction in matrix effect. Moreover, sample dilution and LC-MS/MS injection volume were studied, 3 µL injection volume was found to be the best sensitive condition without sample dilution. The developed method was validated by performing recovery tests at 0.01, 0.05 and 0.1 mg/kg, the average recoveries ranged from 70% to 120%. The reproducibility expressed as relative standard deviation (RSD %) was ≤ 20%.     

A one-pot multi-component reaction for the facile synthesis of some novel 2-aryl thiazolidinones bearing benzimidazole moiety using La(NO<Subscript>3</Subscript>)<Subscript>3</Subscript>·6H<Subscript>2</Subscript>O as an efficient catalyst

A series of new derivatives of 3-benzimidazolyl-2-aryl thiazolidinones, 4a–j are synthesized via a rapid, one-pot, three-component reaction by using La(NO₃)₃·6H₂O as an efficient catalyst from the reaction of 2-aminobenzimidazole, aromatic aldehydes and thioglycolic acid in ethanol at room temperature. These new compounds were characterized by IR, ¹H, ¹³C NMR and mass spectroscopies. An inexpensive and available catalyst, short reaction time, easy workup, good to excellent yields and nontoxic solvent are the advantages of this reaction.     

Synthesis and characterization of room temperature sol–gel-assisted transparent tin-doped magnesium oxide nanoparticles’ protective coating

Journal of Sol-Gel Science and Technology - Using in-situ sol–gel processing, Sn-doped MgO2 nanofilm has been fabricated by spin-coating technique. Cracked and uneven distribution of...     

Synthesis of cobalt-based magnetic nanocrystals from cobalt(II) heterocyclic amine complexes

Research on Chemical Intermediates - Cobalt nanocrystals with different morphologies and magnetic properties were prepared from three cobalt(II) heterocyclic amine precursors in alcoholic solution...     

On quantitative structure of small Ree groups

The main aim of this article is to study quantitative structure of small Ree Groups ²G₂(q). Here, we prove that small Ree groups are uniquely determined by their orders and the set of the number of elements of the same order.     

Justifying the small‐world phenomenon via random recursive trees

We present a new technique for proving logarithmic upper bounds for diameters of evolving random graph models, which is based on defining a coupling between random graphs and variants of random recursive trees. The advantage of the technique is three‐fold: it is quite simple and provides short proofs, it is applicable to a broad variety of models including those incorporating preferential attachment, and it provides bounds with small constants. We illustrate this by proving, for the first time, logarithmic upper bounds for the diameters of the following well known models: the forest fire model, the copying model, the PageRank‐based selection model, the Aiello‐Chung‐Lu models, the generalized linear preference model, directed scale‐free graphs, the Cooper‐Frieze model, and random unordered increasing k‐trees. Our results shed light on why the small‐world phenomenon is observed in so many real‐world graphs. © 2016 Wiley Periodicals, Inc. Random Struct. Alg., 50, 201–224, 2017     

Colorimetric aptamer based assay for the determination of fluoroquinolones by triggering the reduction-catalyzing activity of gold nanoparticles

The authors describe a colorimetric assay for the detection of fluoroquinolones (FQs). It is based on the use of gold nanoparticles (AuNPs) modified with complementary DNA strands and analyte-specific FQ-binding aptamers. The modified AuNPs possess enzyme-like activity that can catalyze the reduction of nitrophenol by NaBH₄. In the absence of ciprofloxacin, the flower-shape coating on the AuNPs prevents the reduction of yellow 4-nitrophenol. In the presence of ciprofloxacin, the DNA/aptamer flower leaves on the AuNPs and the AuNPs can exert their catalytic activity. This results in a color change from yellow to colorless. The assay is highly selective for FQs, fast (1 h), and has a limit of detection as low as 1.2 nM in case of ciprofloxacin. It was successfully applied to the determination of ciprofloxacin in spiked water, serum and milk samples to give LODs of 1.3, 2.6 and 3.2 nM, respectively.     

Colorimetric determination of the microcystin leucine-arginine based on the use of a hairpin aptamer,graphene oxide,and Methylene Blue acting as an optical probe

Microchimica Acta - The authors describe an aptamer-based colorimetric assay for the specific detection of the toxic microcystin leucine-arginine (MC-LR). The method is based on the use of graphene...