Direct determination of trans-resveratrol in human plasma by spectrofluorimetry and second-order standard addition

Trans-resveratrol (RVT) is an antioxidant found in red grapes and their derivatives, which has been related to the reduction of cardiovascular diseases and cancer incidence.This work developed a new spectrofluorimetric-chemometric method for the direct determination of RVT in human plasma. For each measurement, excitation-emission matrices were obtained from 280 to 360 nm (excitation) and from 380 to 550 nm (emission). The strategy adopted in this work combined data treatment with parallel factor analysis (PARAFAC), for extracting the pure analyte signal, using the standard addition method, which permits determinations in the presence of a strong matrix effect caused by plasma analyte-protein binding. Plasma samples were diluted 10 times and, for each, four standard additions of RVT were performed, in triplicate. A specific PARAFAC model was built for the three replicates of each sample, from three-way arrays formed by five measurements (initial sample plus four additions), 17 excitation wavelengths and 86 emission wavelengths. The best models were selected with four factors and accounted for more than 99.90% of the data variance. The loadings obtained were related to RVT and three interferences. The scores related to the analyte were used for linear regressions and all standard addition curves presented correlation coefficients equal or greater than 0.99. Good results were obtained in the concentration range from 0.10 to 5.00 μg mL⁻¹, with recoveries between 94.0 and 110.0%. The proposed method was also validated through the estimates of several figures of merit: sensitivity, analytical sensitivity, selectivity, precision, and limits of detection and quantitation.     

A photophysical study of the interactions in poly(styrene-4-sulphonate)–n-butylvinylether block and random copolymers

Interactions between the moieties responsible for the conformations and hydrophobic microdomains in poly(styrene-4-sulphonate) (PSS) and its copolymers with n-butylvinylether (BVE) were studied by their emission spectra and the lifetimes of the phenyl groups and pyrene used as a photochemical probe. The emission spectra of PSS shows bands due to dimers and higher aggregates as well as the characteristic excimer band. At low concentrations, the random copolymers have spectra similar to that of the free monomer, whereas the block copolymers have spectra like that of PSS. At higher concentrations, the random copolymer also shows these excimer bands, due to interchain interactions. Results from the emission of pyrene prove that the behaviour of the copolymers with approximately 40% BVE seems to be relatively independent of having random or block configurations. Except at low concentrations (<0.05 g/dl), where the block copolymer already has a conformation with “stable” hydrophobic microdomains, both types of copolymers behave similarly. There is an initial aggregate equilibrium between individual chains and aggregates, associated with a relocation of the probes. At higher concentrations, both copolymers suffer a severe change in conformation, due to the formation of “stable” hydrophobic microdomains, resulting from interchain interactions. In both cases the lifetimes of pyrene are of the order of 240 ± 10 ns. Received: 27 August 1998 Accepted: 11 January 1999     

Industrial cutting waste granite dust reinforced cardanol benzoxazine/epoxy resin hybrid composites for high-voltage electrical insulation applications

An attempt has been made to develop hybrid composites from benzoxazine monomer (C-ddm) hybridized with DGEBA epoxy resin (EP) and reinforced with varying weight percentages (20 wt%, 40 wt%, 60 wt%, 80 wt% and 100 wt%) of glycidoxypropyltrimethoxy- silane (GPTMS) functionalized granite dust (GD) obtained from industrial granite cutting and polishing process in order to utilize them for electrical insulation applications. The thermal stability of granite dust reinforced poly(EP-co-C-ddm) composites was studied by TGA analysis. Among the composites samples studied, 100 wt% GD reinforced poly(EP-co-C-ddm) composites possess better thermal stability than that of other neat matrices and composites. Among the composites prepared using varying weight percentages of functionalized GD reinforcement, it was observed that 80 wt% GD reinforced poly(EP-co-C-ddm) composites possesses better hydrophobic character than that of other neat matrices and composites. The value of LOI calculated for neat matrix (poly[EP-co-C-ddm]) and 20 wt%, 40 wt%, 60 wt%, 80 wt% and 100 wt% GD reinforced composites was found to be 22, 28, 34, 40, 43 and 45 respectively. The 80 wt% GD reinforced poly(EP-co-C-ddm) composites possess the higher values of tensile strength and flexural strength of 47 MPa and 140 MPa, respectively than those of their samples. The values of electrical surface resistivity and electrical volume resistivity of all the neat matrices and GD reinforced polybenzoxazine composites were found to be in the order of 10¹² and 10¹³ respectively. The values of dielectric strength obtained from break down voltage (BDV) for neat matrix [poly(EP-co-C-ddm)] and 20 wt%, 40 wt%, 60 wt%, 80 wt% and 100 wt% of GD reinforced poly(EP-co-C-ddm) composites are 15.0, 15.5, 16.5, 17.0, 17.0 and 17.0 kV/mm, respectively. Data obtained from thermal stability, hydrophobic behavior and dielectric studies it was inferred that the hybrid polymer composites developed in the present work can be conveniently used in the form insulators, sealants, adhesives and matrices where application demands at high-performance industrial and engineering applications.