Surface-enhanced Raman spectrometry of chlorinated pesticides

The utility of surface-enhanced Raman scattering (SERS) spectrometry for trace determination of various chlorinated pesticides including chlordan, carbophenothion, bromophos, methyl chloropyrifos, dichloran, linuron, and 1-hydroxychlordene is described. Silver-coated substrates consisting of submicron spheres on solid surfaces were used as SERS-active media. The detection limits for these pesticides are at nanogram levels. The sensitivity and spectral selectivity of this technique for toxic chemical agents are discussed. The results indicate that SERS shows promise for the determination of an important class of chlorinated pesticides.     

Direct determination of salicylamide in serum by matrix isopotential synchronous fluorimetry

A method for the determination of salicylamide at concentrations between 25 and 350 ng ml(-1) by use of matrix isopotential synchronous fluorescence spectrometry (MISF) in combination with derivative techniques is proposed. The method allows the determination of compounds in samples with unknown background fluorescence without the need for tedious pre-separation. Synchronous scans are performed along a trajectory that connects points of identical intensity in a three-dimensional fluorescence spectrum. The unknown analytical signal of the serum is suppressed from the MISF spectrum, by calculating its first derivative at lambda(exc)=324 nm and lambda(em)=392 nm. In order to ensure maximum sensitivity and adequate selectivity, the experimental variables affecting the fluorescence intensity of the salicylamide band at lambda(exc)=328 nm and lambda(em)=418 nm were studied. Based on the results, the determination was performed in an aqueous medium at pH 12 that was adjusted with a sodium phosphate/hydrogen phosphate buffer. Calibration graphs were subjected to a comprehensive statistical analysis. The error propagation has been considered in order to calculate the detection limit by the criterium of Clayton.     

Cooperative Binding of Divalent Diamides by N‐Alkyl Ammonium Resorcinarene Chlorides

N‐Alkyl ammonium resorcinarene chlorides, stabilized by an intricate array of hydrogen bonds leading to a cavitand‐like structure, bind amides. The molecular recognition occurs through intermolecular hydrogen bonds between the carbonyl oxygen and the amide hydrogen of the guests and the cation–anion circular hydrogen‐bonded seam of the hosts, as well as through CH ??? π interactions. The N‐alkyl ammonium resorcinarene chlorides cooperatively bind a series of di‐acetamides of varying spacer lengths ranging from three to seven carbons. Titration data fit either a 1:1 or 2:1 binding isotherm depending on the spacer lengths. Considering all the guests possess similar binding motifs, the first binding constants were similar (K₁: 10² M ^?1) for each host. The second binding constant was found to depend on the upper rim substituent of the host and the spacer length of the guests, with the optimum binding observed with the six‐carbon spacer (K₂: 10³ M ^?2). Short spacer lengths increase steric hindrance, whereas longer spacer lengths increase flexibility thus reducing cooperativity. The host with the rigid cyclohexyl upper rim showed stronger binding than the host with flexible benzyl arms. The cooperative binding of these divalent guests was studied in solution through ¹H NMR titration studies and supplemented by diffusion‐ordered spectroscopy (DOSY), X‐ray crystallography, and mass spectrometry.     

Materially and geometrically non-linear woven composite micro-mechanical model with failure for finite element simulations

A computational micro-mechanical material model of woven fabric composite material is developed to simulate failure. The material model is based on repeated unit cell approach. The fiber reorientation is accounted for in the effective stiffness calculation. Material non-linearity due to the shear stresses in the impregnated yarns and the matrix material is included in the model. Micro-mechanical failure criteria determine the stiffness degradation for the constituent materials. The developed material model with failure is programmed as user-defined sub-routine in the LS-DYNA finite element code with explicit time integration. The code is used to simulate the failure behavior of woven composite structures. The results of finite element simulations are compared with available test results. The model shows good agreement with the experimental results and good computational efficiency required for finite element simulations of woven composite structures.     

Spectrofotometric determination of copper in sugar cane spirit using biquinoline in the presence of ethanol and Triton X-100

The present paper proposes a method for molecular spectrophotometric determination of copper in sugar cane spirits. The copper(I) reacts with biquinoline forming a pink complex with maximum absorption at 545 nm. The reaction occurs in the presence of hydroxylamine, ethanol and Triton X-100 tensioative. Determination of copper is possible in a linear range 0.2-20.0 mgL(-1) with a detection limit 0.05 mgL(-1). The great advantages of the proposed methodology are the elimination of liquid-liquid extraction step and the use of toxic organics solvents, like dioxane, to dissolve the reagent.     

Resolution of Ofloxacin–Ciprofloxacin and Ofloxacin–Norfloxacin Binary Mixtures by Flow-Injection Chemiluminescence in Combination with Partial Least Squares Multivariate Calibration

A flow-injection chemiluminescence (CL) method is described for the determination of ciprofloxacin (CIP), norfloxacin (NOR) and ofloxacin (OFL), commonly used antibiotics of the fluoroquinolones family. The method is based on the CL reaction of the fluoroquinolones with tris(2,2′-bipyridyl) ruthenium(II) and Ce (IV), in sulfuric acid medium. The maximum CL emission, given at 0.45 min for CIP, at 0.35 min for NOR and at 0.04 min for OFL, respectively, were measured, allowing the simple application of the proposed method to the routine analysis of the antibiotics. The methods were applied to the determination of CIP, NOR and OFL, in several pharmaceutical preparations, with very satisfactory results, and validated by a previously reported HPLC method. The time-resolved equipment allowed the measurement of the kinetic evolution of the chemiluminescence signals. In base to the differences in the kinetic behaviour of ofloxacin with respect to ciprofloxacin and norfloxacin, binary mixtures of the drugs were resolved by using the time-resolved chemiluminescence signals, in combination with first-order partial least-squares (PLS) multivariate calibration.     

Lactate and pyruvate levels correlation with lactate dehydrogenase gene expression and glucose consumption in Tamoxifen-resistant MCF-7 cells using capillary electrophoresis with contactless conductivity detection (CE-C4D)

Breast cancer is the second leading cause of cancer death in women after lung cancer. The first-line treatment of metastatic breast cancer in premenopausal women relies on tamoxifen. The development of tamoxifen resistance is not fully understood. In this study, capillary electrophoresis with capacitively coupled contactless conductivity detector was developed to monitor the changes in lactate and pyruvate levels in supernatant media of three models of developed MCF-7 tamoxifen-resistant cells and correlate these metabolites changes with lactate dehydrogenase genes expression and glucose consumption. The electrophoretic separation was achieved under reversed electroosmotic flow conditions. The linear ranges were 0.15–5 and 0.01–1 mM with a correlation coefficient of 0.9966 and 0.9971 and the limits of detection were 0.01 and 0.02 μM for lactate and pyruvate, respectively. Inter- and intrarun accuracy were in the range of 96.88–105.94% with precision (CV, %) of ≤7.35%. The method was completely validated and the results were in agreement with those obtained using the lactate and glucose assay kits. The results revealed a significant increase in both lactate and pyruvate production in the three tamoxifen-resistant MCF-7 cells models compared to control cells. This increase was correlated with the increase of lactate dehydrogenase genes expression and the increase of glucose consumption.