A photo-oxidation procedure using UV radiation/H2O2 for decomposition of wine samples — Determination of iron and manganese content by flame atomic absorption spectrometry

This paper proposes the use of photo-oxidation with UV radiation/H₂O₂ as sample pretreatment for the determination of iron and manganese in wines by flame atomic absorption spectrometry (FAAS). The optimization involved the study of the following variables: pH and concentration of buffer solution, concentrated hydrogen peroxide volume and irradiation time. The evaluation of sample degradation was monitored by measuring the absorbance at the maximum wavelength of red wine (530 nm). Using the experimental conditions established during the optimization (irradiation time of 30 min, oxidant volume of 2.5 mL, pH 10, and a buffer concentration of 0.15 mol L^− 1), this procedure allows the determination of iron and manganese with limits of detection of 30 and 22 μg L^− 1, respectively, for a 5 mL volume of digested sample. The precision levels, expressed as relative standard deviation (RSD), were 2.8% and 0.65% for iron and 2.7% and 0.54% for manganese for concentrations of 0.5 and 2.0 mg L^− 1, respectively. Addition/recovery tests for evaluation of the accuracy were in the ranges of 90%–111% and 95%–107% for iron and manganese, respectively. This digestion procedure has been applied for the determination of iron and manganese in six wine samples. The concentrations varied from 1.58 to 2.77 mg L^− 1 for iron and from 1.30 to 1.91 mg L^− 1 for manganese. The results were compared with those obtained by an acid digestion procedure and determination of the elements by FAAS. There was no significant difference between the results obtained by the two methods based on a paired t-test (at 95% confidence level).     

Preliminary studies of laser-induced breakdown spectrometry for the determination of Ba,Cd, Cr and Pb in toys

The performance of laser-induced breakdown spectrometry (LIBS) for the determination of Ba, Cd, Cr and Pb in toys has been evaluated by using a Nd:YAG laser operating at 1064 nm and an Echelle spectrometer with intensified charge-coupled device detector. Samples were purchased in different cities of São Paulo State market and analyzed directly without sample preparation. Laser-induced breakdown spectrometry experimental conditions (number of pulses, delay time, integration time gate and pulse energy) were optimized by using a Doehlert design. Laser-induced breakdown spectrometry signals correlated reasonably well with inductively coupled plasma optical emission spectrometry (ICP OES) concentrations after microwave-assisted acid digestion of selected samples. Thermal analysis was used for polymer identification and scanning electron microscopy to visualize differences in crater geometry of different polymers employed for toy fabrication. Results indicate that laser-induced breakdown spectrometry can be proposed as a rapid screening method for investigation of potentially toxic elements in toys. The unique application of laser-induced breakdown spectrometry for identification of contaminants in successive layers of ink and polymer is also demonstrated.     

Synthetic,Mechanistic, and Theoretical Studies on the Generation of Iridium Hydride Alkylidene and Iridium Hydride Alkene Isomers

Experimental and theoretical studies on equilibria between iridium hydride alkylidene structures, [(Tp^Me2)Ir(H){?C(CH₂R)ArO }] (Tp^Me2=hydrotris(3,5‐dimethylpyrazolyl)borate; R=H, Me; Ar=substituted C₆H₄ group), and their corresponding hydride olefin isomers, [(Tp^Me2)Ir(H){R(H)C? C(H)OAr}], have been carried out. Compounds of these types are obtained either by reaction of the unsaturated fragment [(Tp^Me2)Ir(C₆H₅)₂] with o‐C₆H₄(OH)CH₂R, or with the substituted anisoles 2,6‐Me₂C₆H₃OMe, 2,4,6‐Me₃C₆H₂OMe, and 4‐Br‐2,6‐Me₂C₆H₂OMe. The reactions with the substituted anisoles require not only multiple C? H bond activation but also cleavage of the Me? OAr bond and the reversible formation of a C? C bond (as revealed by ¹³C labeling studies). Equilibria between the two tautomeric structures of these complexes were achieved by prolonged heating at temperatures between 100 and 140 °C, with interconversion of isomeric complexes requiring inversion of the metal configuration, as well as the expected migratory insertion and hydrogen‐elimination reactions. This proposal is supported by a detailed computational exploration of the mechanism at the quantum mechanics (QM) level in the real system. For all compounds investigated, the equilibria favor the alkylidene structure over the olefinic isomer by a factor of between approximately 1 and 25. Calculations demonstrate that the main reason for this preference is the strong Ir–carbene interactions in the carbene isomers, rather than steric destabilization of the olefinic tautomers.     

Comparison of adsorption equilibrium of fructose, glucose and sucrose on potassium gel-type and macroporous sodium ion-exchange resins

Adsorption equilibrium of fructose, glucose and sucrose was evaluated on sulfonated poly(styrene-co-divinylbenzene) cation-exchange resins. Two types of resins were used: potassium (K⁺) gel-type and sodium (Na⁺) macroporous resins. Influence of the cation and effect of the resin structure on adsorption were studied. The adsorption isotherms were determined by the static method in batch mode for mono-component and multi-component sugar mixtures, at 25 and 40 °C, in a range of concentrations between 5 and 250 g L⁻¹. All adsorption isotherms were fitted by a linear model in this range of concentrations. Sugars were adsorbed in both resins by the following order: fructose > glucose > sucrose. Sucrose was more adsorbed in the Na⁺ macroporous resin, glucose was identically adsorbed, and fructose was more adsorbed in the K⁺ gel-type resin. Data obtained from the adsorption of multi-component mixtures as compared to the mono-component ones showed a competitive effect on the adsorption at 25 °C, and a synergetic effect at 40 °C. The temperature increase conducted to a decrease on the adsorption capacity for mono-component sugar mixtures, and to an increase for the multi-component mixtures. Based on the selectivity results, K⁺ gel-type resin seems to be the best choice for the separation of fructose, glucose and sucrose, at 25 °C.     

Synthesis and application of a peroxidase-like molecularly imprinted polymer based on hemin for selective determination of serotonin in blood serum

This work reports the preparation of a molecularly imprinted polymer (MIP) for selective catalytic detection of serotonin (5-hydroxytryptamine, 5-HT). The process is based on the synthesis of polymers with hemin introduced as the catalytic center to mimic the active site of peroxidase. The copolymer MIP, containing artificial recognition sites for 5-HT, has been prepared by bulk polymerization using methacrylic acid (MAA) and hemin as the functional monomers, and ethylene glycol dimethacrylate (EGDMA) as the cross-linker. For the determination of 5-HT, a flow injection analysis system coupled to an amperometric detector was optimized using multivariate analysis. The effects of different parameters, such as pH, buffer flow rate, buffer nature, peroxide concentration and sample volume were evaluated. After optimizing the experimental conditions, a linear response range from 1.0 up to 1000.0 μmol L⁻¹ was obtained with a sensitivity of 0.4 nA/μmol L⁻¹. The detection limit was found to be 0.30 μmol L⁻¹, while the precision values (n = 6) evaluated by relative standard deviation (R.S.D.) were, respectively, 1.3 and 1.7% for solutions of 50 and 750 μmol L⁻¹ of 5-HT. No interference was observed by structurally similar compounds (including epinephrine, dopamine and norepinephrine), thus validating the good performance of the imprinted polymer. The method was applied for the determination of 5-HT in spiked blood serum samples.     

Sequential injection analysis (SIA) and response surface methodology: A versatile small volume approach for optimization of photo-Fenton processes

Optimization of photo-Fenton degradation of copper phthalocyanine blue was achieved by response surface methodology (RSM) constructed with the aid of a sequential injection analysis (SIA) system coupled to a homemade photo-reactor. Highest degradation percentage was obtained at the following conditions [H₂O₂]/[phthalocyanine] = 7, [H₂O₂]/[FeSO₄] = 10, pH = 2.5, and stopped flow time in the photo reactor = 30 s. The SIA system was designed to prepare a monosegment containing the reagents and sample, to pump it toward the photo-reactor for the specified time and send the products to a flow-through spectrophotometer for monitoring the color reduction of the dye. Changes in parameters such as reagent molar ratios, residence time and pH were made by modifications in the software commanding the SI system, without the need for physical reconfiguration of reagents around the selection valve. The proposed procedure and system fed the statistical program with degradation data for fast construction of response surface plots. After optimization, 97% of the dye was degraded.     

Structural Factors and Mechanisms Underlying the Improved Photodynamic Cell Killing with Silicon Phthalocyanine Photosensitizers Directed to Lysosomes Versus Mitochondria

The phthalocyanine photosensitizer Pc 4 has been shown to bind preferentially to mitochondrial and endoplasmic reticulum membranes. Upon photoirradiation of Pc 4-loaded cells, membrane components, especially Bcl-2, are photodamaged and apoptosis, as indicated by activation of caspase-3 and cleavage of poly(ADP-ribose) polymerase, is triggered. A series of analogs of Pc 4 were synthesized, and the results demonstrate that Pcs with the aminopropylsiloxy ligand of Pc 4 or a similar one on one side of the Pc ring and a second large axial ligand on the other side of the ring have unexpected properties, including enhanced cell uptake, greater monomerization resulting in greater intracellular fluorescence and three-fold higher affinity constants for liposomes. The hydroxyl-bearing axial ligands tend to reduce aggregation of the Pc and direct it to lysosomes, resulting in four to six times more killing of cells, as defined by loss of clonogenicity, than with Pc 4. Whereas Pc 4-PDT photodamages Bcl-2 and Bcl-xL, Pc 181-PDT causes much less photodamage to Bcl-2 over the same dose–response range relative to cell killing, with earlier cleavage of Bid and slower caspase-3-dependent apoptosis. Therefore, within this series of photosensitizers, these hydroxyl-bearing axial ligands are less aggregated than is Pc 4, tend to localize to lysosomes and are more effective in overall cell killing than is Pc 4, but induce apoptosis more slowly and by a modified pathway.     

Silica supported phospholipid layers doped with GM1: A comparison between different methods

A method to coat hydrophobic surfaces with lipid molecules in a reproducible manner and in which the lipid molecules are resistant to detergent washings, would benefit the development of new ELISA assays. This work presents different approaches to build 1,2-dioleolyl-sn-glycero-3-phosphocholine (DOPC) layers doped with a monosialoganglioside (GM1) supported on silica surfaces, which are stable toward buffer rinsing and washing with surfactant (Tween 20). The three methods employed were: method 1, coadsorption of DOPC:GM1 (0-10 mol%) with the surfactant n-dodecyl-beta-D-maltoside (DDM) from micellar solutions, with successive adsorption and rinsing steps; method 2, vesicle fusion from DOPC: GM1 (0-10 mol%) liposomes; and method 3, deposition of GM1 from organic solvent (chloroform) and exposure to an aqueous environment (hydration method). The vesicle fusion method was also tested in polystyrene surfaces. Cholera toxin subunit B (CTB) was used to detect the presence of GM1 on the formed layers. The results indicated that the vesicle fusion was the only method that was successful in creating stable mono- and bilayers onto hydrophobized and hydrophilic silica, respectively. The mixed micellar solution method was suitable for creating pure lipid (DOPC) monolayers but the incorporation of GM1 in the micelles led to monolayers which were very unstable with respect to buffer rinsing. The hydration method led to monolayers of GM1 that were partly rinsed off by a continuous buffer flow. Adsorption of CTB was found to be proportional to the amount of GM1 present in the liposomes. The amount of CTB adsorbed onto the lipid bilayers was roughly the double as the one determined on the monolayers with the same liposome compositions. The vesicle fusion method was also able to create monolayers of pure DOPC and DOPC:10 mol% GM1 on the polystyrene surfaces.     

LC Method for Studies on the Stability of Sibutramine in Soft Gelatin Capsules

A sensitive and rapid liquid chromatographic method was successfully developed and validated for the determination of sibutramine hydrochloride in bulk and capsules. Sibutramine in the presence of its degradation products was analyzed using UV detection at 225 nm. Chromatography was performed on a reversed-phase C₈ (150 × 4.0 mm I.D., 5 μm) analytical column under isocratic conditions. The mobile phase was composed of acetonitrile:water (aqueous phase containing 0.3% triethylamine and pH adjusted to 7.0) (75:25, v/v) at a flow-rate of 1.1 mL min⁻¹. No chromatographic interference was found during the analysis. Light was the stress condition which most contributed to sibutramine degradation. The method showed a linear response (r > 0.999) from 30 to 90 μg mL⁻¹. The mean recovery for capsules was 101.2%. Inter-day assays showed relative standard deviations of 0.42 and 1.62% for bulk and capsules, respectively. The developed method is able to separate sibutramine from its major degradation products and it may be used in the quality control of this active pharmaceutical ingredient in both bulk and capsules.