Multi-residue determination of 130 multiclass pesticides in fruits and vegetables by gas chromatography coupled to triple quadrupole tandem mass spectrometry

A multi-residue method has been developed and validated for the simultaneous quantification and confirmation of around 130 multiclass pesticides in orange, nectarine and spinach samples by GC-MS/MS with a triple quadrupole analyzer. Compounds have been selected from different chemical families including insecticides, herbicides, fungicides and acaricides. Three isotopically labeled standards have been used as surrogates in order to improve accurate quantitation. Samples were extracted by using accelerated solvent extraction (ASE) with ethyl acetate. In the case of spinach, an additional clean-up step by gel permeation chromatography was applied. Determination was performed by GC-MS/MS in electron ionization mode acquiring two MS/MS transitions for each analyte. The intensity ratio between quantitation transition (Q) and identification transition (q) was used as confirmatory parameter (Q/q ratio). Accuracy and precision were evaluated by means of recovery experiments in orange, nectarine, and spinach samples spiked at two concentration levels (0.01 and 0.05 mg/kg). Recoveries were, in most cases, between 70% and 120% and RSD were below 20%. The limits of quantification objective for which the method was satisfactorily validated in the three samples matrices were for most pesticides 0.01 mg/kg. Matrix effects over the GC-MS/MS determination were tested by comparison of reference standards in pure solvent with matrix-matched standards of each matrix. Data obtained showed enhancement of signal for the majority of analytes in the three matrices investigated. Consequently, in order to reduce the systematic error due to this effect, quantification was performed using matrix-matched standard calibration curves. The matrix effect study was extended to other food matrices such as raisin, paprika, cabbage, pear, rice, legume, and gherkin, showing in all cases a similar signal enhancement effect.     

The heavy quarkonium spectrum at order mαslnαs

We compute the complete leading-log terms of the next-to-next-to-next-to-leading-order corrections to potential NRQCD. As a by-product we obtain the leading logs at O(mα_s⁵) in the heavy quarkonium spectrum. These leading logs, when Λ_QCDmα_s², give the complete O(mα_s⁵lnα_s) corrections to the heavy quarkonium spectrum.     

Fingerprint analysis and the application of HPTLC to the determination of identity and quality of botanicals, from an industry perspective

There are many examples of botanical identity methodology currently in use today; all have associated levels of confidence and, hence, application for their intended purpose. This paper addresses the application of some of these methods to identify and qualify commonly traded herbs. The relevance of botanical identity and quality within the dietary supplement industry has seen a dramatic increase in the last several years, and now with the current Good Manufacturing Practices (cGMPs) recently published and the requirement for 100% identity testing, there is an increased need for reliable methods of analysis and subsequent interpretation of the results or data derived from these methods, given the diversity of samples and matrixes seen on a daily basis in a commercial setting. Example applications of methods described herein illustrate how one can confidently and effectively satisfy the 100% identity rule of the cGMPs to identify crude raw materials and their powdered or liquid extracts as well as identify a majority of such ingredients in finished products with diverse matrixes. The three techniques discussed in this paper are viewed from a qualitative perspective with primary emphasis on the application of HPTLC to a variety of complex samples with varying degrees of difficulty of analysis and interpretation. The three methods discussed are (1) HPTLC, for its fingerprint/pattern recognition capabilities as well as marker compound analysis; (2) microscopy, for identification/recognition of unique cellular, anatomic features and characteristics of the target plant or adulterants; and (3) HPLC for marker compound identification, quantitation, and/or other fingerprint qualities it may contribute to the data set. To support the applications and methods described herein, this paper presents four key approaches to assist in the interpretation of the data collected in order to correctly determine the identity of botanicals and their powdered extracts: the "marker approach," the "multicomponent-based approach", the "pattern approach," and the "multipattern approach", and how these approaches can be used with a vanguard/rearguard strategy in analytical testing as well as forming a basis for the "functional fingerprint" and the concept of phytoequivalence.     

The Lamb shift in dimensional regularisation

We present a simple derivation of the Lamb shift using effective field theory techniques and dimensional regularisation.     

Crystal structures and biological activity of 1,1,4‐triphenyl‐substituted 1,3‐enyne compounds

1,3‐Enyne structural motifs are versatile building blocks in organic synthesis and occur widely in various natural products with many of them being highly active as cytotoxic macrolides and antitumour antibiotics. This article presents the crystal structure of three 1,1,4‐triphenyl‐substituted 1,3‐enynes, viz. 4‐(2‐methylphenyl)‐1,1‐diphenylbut‐1‐en‐3‐yne, C₂₃H₁₈ ( 1 ), 4‐(2‐methoxyphenyl)‐1,1‐diphenylbut‐1‐en‐3‐yne, C₂₃H₁₈O ( 2 ), and 4‐(4‐nitrophenyl)‐1,1‐diphenylbut‐1‐en‐3‐yne, C₂₂H₁₅NO₂ ( 3 ). The benzene ring at position 4 of the but‐1‐en‐3‐yne group bears a weakly activating methyl group in compound 1 , a moderately activating methoxy group in 2 and a strongly deactivating nitro group in 3 . The crystal structures of 1 and 3 both have monoclinic symmetry, while that of 2 is orthorhombic, and all of them have one molecule in the asymmetric unit. All three compounds were investigated for their antibacterial and antifungal activities. Interestingly, enyne 2 is the only compound tested that inhibited the growth of Aspergillus niger.     

The noisy Hegselmann-Krause model for opinion dynamics

In the model for continuous opinion dynamics introduced by Hegselmann and Krause, each individual moves to the average opinion of all individuals within an area of confidence. In this work we study the effects of noise in this system. With certain probability, individuals are given the opportunity to change spontaneously their opinion to another one selected randomly inside the opinion space with different rules. If the random jump does not occur, individuals interact through the Hegselmann-Krause’s rule. We analyze two cases, one where individuals can carry out opinion random jumps inside the whole opinion space, and other where they are allowed to perform jumps just inside a small interval centered around the current opinion. We found that these opinion random jumps change the model behavior inducing interesting phenomena. Using pattern formation techniques, we obtain approximate analytical results for critical conditions of opinion cluster formation. Finally, we compare the results of this work with the noisy version of the Deffuant et al. model [G. Deffuant, D. Neu, F. Amblard, G. Weisbuch, Adv. Compl. Syst. 3, 87 (2000)] for continuous-opinion dynamics.     

Voltammetric Determination of Metronidazole Using a Sensor Based on Electropolymerization of α‐Cyclodextrin over a Carbon Paste Electrode

An electrochemical sensor for metronidazole (MTZ) was built via the surface modification of a carbon paste electrode (CPE) by a film obtained through electropolymerization of α‐cyclodextrin (CPE_α‐CD). The CPE_α‐CD was characterized by cyclic voltammetry (CV) and atomic force microscopy (AFM), by both techniques was demonstrated that the polymer film is coating the electrode surface. The electroreduction behaviour of MTZ in HClO₄ media as a supporting electrolyte was studied by differential‐pulse voltammetric (DPV) technique. The DPV electrochemical process was observed to be diffusion controlled and irreversible. Under optimal conditions, the peak current was proportional to MTZ concentration in the range of 0.5 to 103.0 μM with a detection limit of 0.28±0.02 μM. The method was successfully applied to quantify of MTZ in pharmaceutical formulations. In addition, this proposed MTZ sensor exhibited good reproducibility, long‐term stability and fast current response.     

Allylic Reactions of Benzocyclopropenes. Discrimination of halogen substituents in 1, 1-Dihalogenobenzocyclopropenes

Reaction of 1, 1-dichloro-2, 5-diphenylbenzocyclopropene ( 10a ) with 1 equiv. of silver fluoride yields 1-chloro-1-fluoro-2, 5-diphenylbenzocyclopropene ( 10c ). Both 10a and 10c react with excess silver fluoride to give the difluoro compound 10b . Both 10b and 10c are also prepared via cyclo-additions of 1, 2-dichloro-3, 3-difluorocyclopropene ( 14 ) or 1, 2, 3-flurocyclopropene ( 13 ) with diphenylbutadiene and subsequent aromatization with base. Similarly. 1-chloro-1-fluorobenzocyclopropene ( 16 ) is accessible from butadiene and 13 .     

Formation and dissolution processes of the 6-thioguanine (6TG) self-assembled monolayer. A kinetic study

This is a report on the kinetics of the destruction and formation processes of the 6-thioguanine self-assembled monolayer (6TG SAM) on a mercury electrode from acid solutions by chronoamperometry. The destruction of the 6TG SAM that has been previously formed under open circuit potential conditions is carried out by stepping the potential from an initial value where the chemisorbed layer is stable up to potentials where the molecules are no longer chemisorbed. The destruction of the SAM has been described by a model that involves three types of contributions: (i) a Langmuir-type adsorption process, (ii) a 2D nucleation mechanism followed by a growth controlled by surface diffusion, and (iii) a 2D nucleation mechanism followed by a growth at a constant rate. The nonlinear fit of the experimental transients by using this procedure allows the quantitative determination of the individual contributions to the overall process. The kinetics of the formation process is studied under electrochemical conditions. The chronoamperometric experiment allows us to monitor the early stages of 6TG SAM formation. The implications of the physisorbed state at low potentials in the type of monolayer formation and destruction processes as well as the influence of temperature are also discussed.