Column switching liquid chromatography and post-column photochemically fluorescence detection to determine imidacloprid and 6-chloronicotinic acid in honeybees

The determination of imidacloprid and its main metabolite (6-chloronicotinic acid) in honeybees was performed by liquid chromatography with post-column photochemical derivatisation in alkaline medium and fluorescence detection. The compounds were extracted from honeybees with acetone under ultrasound conditions prior to liquid-liquid partition with dichloromethane. The separation of extract components was performed using a 50 mm x 4.6 mm i.d. short column packed with 5 microm Aquasil C(18) using an acetonitrile:water gradient program as mobile phase. Injection of samples in 0.1 mol L(-1) H(3)PO(4)/KH(2)PO(4) buffer solution (pH 3) improved the chromatographic separation between the most polar components of matrix and the 6-chloronicotinic acid. Matrix components were removed to waste using an on-line clean-up method previously to post-column reaction. Limits of quantification were 0.3 and 5.0 microg L(-1) (corresponding to 1.2 and 20.0 microg kg(-1) in the honeybee sample) for imidacloprid and 6-chloronicotinic acid, respectively. The recovery was ranged from 80.2 to 91.7% with a relative standard deviation lower than 9.0%.     

The use of multiple correspondence analysis for the evaluation of inter-laboratory comparisons

Participation in inter-laboratory comparisons (ILC) is one of the recommended means of external quality control according to ISO/IEC 17025:2005. Providers of ILC or proficiency test (PT) schemes collect, besides the measurement results on the test samples, information on the sample treatment and measurement procedure. The objective of this paper is to evaluate in a non-traditional way, using numerical and non-numerical data provided by the participants in IMEP-20 (trace elements in tuna fish), the additional information concerning the applied analytical methods and the accreditation/nomination status. Arsenic was taken as an example. The basic statistical procedure for the evaluation of questionnaire information was the multiple correspondence analysis (MCA). Univariate clustering techniques were applied for the categorization of the numerical data (measurement values). The methodology of the evaluation of supplementary non-numeric information used in this paper might serve (a) to providers of ILC (PT) schemes to modify/improve their questionnaires and (b) to give laboratories better guidance in the methods used for the determination of various analytes in different matrices. This paper is meant serve as a guide for the possible interpretation of the questionnaires accompanying ILC schemas. Presented at the 3rd International Conference on Metrology, November 2006, Tel Aviv, Israel     

Analysis of amoxicillin in human urine by photo-activated generation of fluorescence excitation-emission matrices and artificial neural networks combined with residual bilinearization

Fluorescence excitation-emission data recorded for amoxicillin after photo-activated reaction with periodate have been processed by a novel second-order multivariate method based on the combination of artificial neural networks and residual bilinearization (ANN/RBL), since the signals bear a strong non-linear relation with the analyte concentration. The selected chemometric methodology is employed for the first time to evaluate experimental non-linear second-order spectral information. Due to severe overlapping between the emission profiles for the analyte reaction product and for the urine background, calibration was done using different spiked urine samples. This allowed for the determination of amoxicillin in test spiked urines, other than those employed for calibration. When new urine samples containing a fluorescent anti-inflammatory were analyzed, accurate prediction in the presence of unexpected components required the achievement of the second-order advantage, which is provided by the post-training RBL procedure. Amoxicillin was also determined by ANN/RBL in a series of real urine samples, which allowed one to perform a comparison study with the reference high-performance liquid chromatographic technique.     

Experimental study of non-linear second-order analytical data with focus on the second-order advantage

Three different experimental systems have been studied regarding the determination of analytes in complex samples, using non-linear second-order instrumental data, which are intrinsically able to provide the second-order advantage. This permits the quantitation of calibrated analytes in the presence of unexpected sample components, although a suitable algorithm is required. The recently described combination of artificial neural networks with post-training residual bilinearization has been applied to the three data sets, with successful results concerning prediction accuracy and precision, as well as profile recovery for the potential interferents in test samples. The studies involve: (1) the determination of two pharmaceuticals in the presence of an unexpected excipient by absorbance-pH matrix measurements, (2) the quantitation of iron(II) by its catalytic effect on the kinetics of the bromate oxidation of a colorant in the presence of a second interfering organic dye, and (3) the analysis of the antibiotic amoxicillin by fluorescence excitation-emission matrices in the presence of a fluorescent anti-inflammatory. The prediction results were compared and shown to be significantly better than those yielded by the unfolded partial least-squares/residual bilinearization model, due to the non-linear nature of the studied data.     

Formation and Reversible Morphological Transition of Bicontinuous Nanospheres and Toroidal Micelles by the Self‐Assembly of a Crystalline‐b‐Coil Diblock Copolymer

We herein report the formation of two complex nanostructures, toroidal micelles and bicontinuous nanospheres, by the self‐assembly of the single structurally simple crystalline‐b‐coil diblock copolymer poly[bis(trifluoroethoxy)phosphazene]‐b‐poly(styrene), PTFEP‐b‐PS, in one solvent (THF) and without additives. The nature of these nanostructures in solution was confirmed by DLS and cryo‐TEM experiments. The two morphologies are related by means of a new type of reversible morphological evolution, bicontinuous‐to‐toroidal, triggered by changes in the polymer concentration. WAXS experiments showed that the degree of crystallinity of the PTFEP chains located at the core of the toroids was higher than that in the bicontinuous nanospheres, thus indicating that the final morphology of the aggregates is mostly determined by the ordering of the PTFEP core‐forming blocks.     

Magnetic polyoxometalates: anisotropic exchange interactions in the moiety of [(NaOH2)Co3(H2O)(P2W15O56)2]17-

The magnetic exchange interactions in a C0(3)(11) moiety encapsulated in Na(17) [(NaOH(2))Co(3)(H(2)O)(P(2)W(15)O(56))(2)] (NaCo(3)) were studied by a combination of magnetic measurements (magnetic susceptibility and low-temperature magnetization), with a detailed Inelastic Neutron Scattering (INS) investigation. The novel structure of the salt was determined by X-ray crystallography. The ferromagnetic Co(3)O(14) triangular cluster core consists of three octahedrally oxo-coordinated Co(II) ions sharing edges. According to the single-ion anisotropy and spin-orbit coupling usually assumed for octahedral Co(II) ions, the appropiate exchange Hamiltonian to describe the ground-state properties of the isosceles triangular Co(3) spin cluster is anisotropic and is expressed as H = - 2sigma(alpha)(=)(x,y,z)(J(alpha)(12)S(1alpha)S(2alpha) + J(alpha)(23)S(2alpha)S(3alpha) + J(alpha)(13)S(1alpha)S(3alpha)), where J(alpha) are the components of the exchange interactions between the Co(II) ions. To reproduce the INS data, nonparallel anisotropic exchange tensors needed to be introduced, which were directly connected to the molecular symmetry of the complex. The following range of parameters (value +/- 0.5 cm(-1)) was found to reproduce all experimental information while taking magnetostructural relations into account: J(x)(12) = J(y)(13) = 8.6 cm(-1); J(y)(12) = J(x)(13) = 1.4 cm(-1); J(z)(12) = J(z)(13) = 10.0 cm(-1); J(x)(23) = J(y)(23) = 6.5 cm(-1) and = 3.4 cm(-1).     

Lanthanide(III) Nitrate Complexes of Two 17 Membered N3O2-Donor Macrocycles

The interaction of lanthanide(III) ions with two N₃O₃-macrocycles, L¹ and L², derived from 2,6-bis(2-formylphenoxymethyl)pyridine and 1,2-diaminoethane has been investigated. Schiff-base macrocyclic lanthanide(III) complexes LnL¹(NO₃)₃ · xH₂O (Ln = Nd, Sm, Eu or Lu) have been prepared by direct reaction of L¹ and the appropriate hydrated lanthanide nitrate. The direct reaction between the diamine macrocycle L² and the hydrated lanthanide(III) nitrates yields complexes LnL²(NO₃)₃· H₂O only for Ln = Dy or Lu. The reduction of the Schiff-base macrocycle decreases the complexation capacity of the ligand towards the Ln(III) ions. The complexes have been characterised by elemental analysis, molar conductivity data, FAB mass spectrometry, IR and, in the case of the lutetium complexes, ¹H NMR spectroscopy.     

Dynamic rheology and relaxation time spectra of oil‐based self‐degradable gels

In oil well treatments, such as matrix stimulations or water shut‐off, it is often necessary to temporary isolate or protect productive zones with chemical diverting agents. In this work, a solution of peroxide crosslinked styrene‐butadiene rubber (SBR) has been transformed to a self‐degradable gel system by adding hydroperoxide as a degradation agent to the formulation. This oil‐based self‐degradable gel has been characterized by linear oscillatory rheometry. In situ and ex situ experiments were performed to evaluate the evolution of crosslinking and degradation reactions, including the liquid‐solid transition. Relaxation time spectra were calculated from dynamic mechanical frequency sweeps. Structural changes in the polymer network were visible within the relaxation time spectra, since it qualitatively showed the contribution of local simple entanglements and chemical covalent bonds to the final rheological behavior. The influence of peroxide concentration, polymer concentration, hydroperoxide concentration, and temperature have been studied and described in terms of rheological changes. Finally, a hydrogen donor aromatic solvent was used as scavenger to retard both crosslinking and degradation reactions. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 433–444     

Plasticization and cocrystallization in LLDPE/wax blends

The structure and thermal properties of linear low‐density polyethylene (LLDPE)/medium soft paraffin wax blends, prepared by melt mixing, were investigated by differential scanning calorimetry (DSC) and small‐ and wide‐angle X‐ray scattering (SAXS and WAXS). The blends form a single phase in the melt as determined by SAXS. Upon cooling from the melt, two crystalline phases develop for blends with more than 10 wt % wax characterized by widely different melting points. The wax acts as an effective plasticizer for LLDPE, decreasing both its crystallization and melting temperature. The higher melting point crystalline phase is formed by less branched LLDPE fractions. On the other hand, the lower melting point crystalline phase is a wax‐rich phase constituted by cocrystals of extended chain wax and short linear sequences of highly branched LLDPE chains. The presence of cocrystals was evidenced by standard DSC results, successive self‐nucleation and annealing (SSA) thermal fractionation and by the detection of a new SAXS signal attributed to the lamellar long period of the cocrystals. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1469–1482     

On the mechanism of hydrogen transfer in the HSCH(O) <--> (S)CHOH and HSNO <--> SNOH reactions

The 1,3-intramolecular hydrogen transfer in the HSCH(O) <--> (S)CHOH and HSNO <--> SNOH reactions is studied through density functional theory calculations. The reaction force together with structural and electronic properties is monitored along the reaction path to characterize the mechanism of hydrogen transfer. It is found that in both reactions the hydrogen transfer is activated by the structural rearrangement of the backbone atoms that allow the electrostatic interactions to promote the hydrogen transfer in a stepwise mechanism.