Voltammetric Determination of Folic Acid Using a Graphite Paste Electrode

A simple differential pulse voltammetric method based on a graphite paste electrode (GPE) was developed for the quantitative determination of folic acid (FA) in tablets. The electrode exhibits a clear improvement of the current response. A linear response in the electroanalytical approach exists from 4.97×10^?6 to 2.94×10^?5 mol L^?1 with a limit of detection of about 2.67×10^?6 mol L^?1 in KCl solutions. The developed procedure was tested by recovery studies and compared with spectrophotometric and chromatographic methods. The results are described and discussed in the light of existing literature.     

Response surface methodology (RSM) as a tool for optimization in analytical chemistry

A review about the application of response surface methodology (RSM) in the optimization of analytical methods is presented. The theoretical principles of RSM and steps for its application are described to introduce readers to this multivariate statistical technique. Symmetrical experimental designs (three-level factorial, Box-Behnken, central composite, and Doehlert designs) are compared in terms of characteristics and efficiency. Furthermore, recent references of their uses in analytical chemistry are presented. Multiple response optimization applying desirability functions in RSM and the use of artificial neural networks for modeling are also discussed.     

Development of a certified reference material for cachaça: an effective material for quality assurance

Cachaça is the typical and genuine denomination for the sugar cane beverage produced in Brazil. It has an alcoholic content between 38 and 48 % by volume, at 20 °C, and is obtained from the distillation of fermented sugar cane juice with the possible addition of up to 6 g/L of sugar, expressed by sucrose. This paper aims to outline the approach taken for the certification of the mass fraction of individual alcohols and their associated uncertainties in a cachaça certified reference material (CRM) produced by the Organic Analysis Laboratory of the Chemical Metrology Division of Inmetro. The requirements of ISO Guide 31, ISO Guide 34 and ISO Guide 35 were followed for the certification. This included the assessment of the degree of homogeneity of the material, the short-term stability study to determine the transport conditions, the long-term stability study to establish the shelf life and storage conditions of the CRM and the characterization process. The certified values were determined by two analytical techniques: gas chromatography coupled to mass spectrometry and gas chromatography with flame ionization detection. In order to support the routine testing of cachaça, in helping analytical laboratories validate and standardize their methods, the certified reference material (CRM 02.1/10.003b) was developed and certified for the mass fractions of methanol (9.18 mg/100 g ± 0.82 mg/100 g), 2-butanol (4.15 mg/100 g ± 0.40 mg/100 g), 1-butanol (1.30 mg/100 g ± 0.18 mg/100 g), isobutanol (24.0 mg/100 g ± 1.0 mg/100 g) and 1-propanol (29.4 mg/100 g ± 1.3 mg/100 g) in a spiked cachaça.     

Non-hydrolytic sol–gel synthesis of polypropylene/TiO2 composites by reactive extrusion

Journal of Sol-Gel Science and Technology - An original way to synthesise polypropylene/titanium dioxide (PP/TiO2) composites combining non-hydrolytic sol–gel chemistry and reactive extrusion...     

Comprehensive two-dimensional liquid chromatography-based quali-quantitative screening of aqueous phases from pyrolysis bio-oils

Pyrolysis processes are an alternative to minimize the environmental problem associated to agrifood industrial wastes. The main product resulting from these processes is a high-value liquid product, called bio-oil. Recently, the use of comprehensive two-dimensional liquid chromatography (LC × LC) has been demonstrated as a useful tool to improve the characterization of the water-soluble phases of bio-oils, considering their complexity and high water content. However, the precise composition of bio-oils from different agrifood byproducts is still unknown. In the present study, the qualitative and quantitative screening of eight aqueous phases from different biomasses, not yet reported in the literature, using LC × LC is presented. The two-dimensional approach was based on the use of two reverse phase separations. An amide column in the first dimension together with a C18 column in the second dimension were employed. Thanks to the use of diode array and mass spectrometry detection, 28 compounds were identified and quantified in the aqueous phase samples with good figures of merit. Samples showed a distinct quali-quantitative composition and a great predominance of compounds belonging to aldehydes, ketones and phenols, most of them with high polarity.     

On the variational convergence of fuzzy sets in metric spaces

Kaleva [9] has studied the relationships between the metric convergencesH andD of fuzzy convex sets on Euclidean spaces. The distanceH between two fuzzy set is given by Hausdorff distance of their sendographs, whileD is the supremum of the Hausdorff distances of the level sets corresponding to the fuzzy sets. The aim of this paper is to compareH andD with the variational convergence, called γ-convergence (see De Giorgi and Franzoni [3]). Our analysis which is carried out in the setting of metric spaces (not necessarily locally compact or vector spaces), improves Kaleva's results.

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Sunto Kaleva ha investigato in [9] le relazioni esistenti tra due convergenze metriche, detteH eD, di sottoinsiemi fuzzy di spazi euclidei finito-dimensionali. In questo articolo le convergenzeH eD (la loro definizione dipende dalla distanza di Hausdorff tra insiemi compatti) sono confrontate con la convergenza variazionale, detta γ-convergenza, introdotta da De Giorgi and Franzoni in [3] nel contesto degli spazi topologici. Tale confronto con la γ-convergenza (vedi Teorema 3.7), svolto nell'ambito degli spazi metrici (non necessariamente, localmente compatti o lineari) migliora ed estende i precedenti risultati di Kaleva.

     

Exploiting the bead injection concept for sequential determination of copper and mercury ions in river-water samples

A procedure involving bead-injection concept and sequential determination of copper and mercury ions in river-water samples is proposed. The method is based on the solid-phase extraction of both metal ions on the same beads surface (Chelex 100 resin) and in their subsequent reaction with the colorimetric reagents (APDC and Dithizone for copper and mercury ions, respectively). For this task, a resin mini-column is established in the optical path by the selection, introduction and trapping of a defined volume of the Chelex-100 resin beads suspension in the flow system. The passage of the sample solution through the resin mini-column promotes the sorption of Cu(II) ions and, making the APDC colorimetric reagent flows through the beads, the formation of the coloured complex on the solid phase surface occurs. The absorbance of the formed APDC-Cu complex is then monitored at 436 nm and the spent beads are discarded. Packing another resin mini-column in the flow cell and repeating the concentration step it is possible to carried out the mercury determination by using Dithizone as reagent. The absorbance of the Dithizone-Hg complex is monitored at 500 nm. After each measurement, the spent beads are wasted and a new portion of fresh one is trapped in the system, letting it ready for the next measurement. The bead injection system is versatile and can be used to concentrate different sample volumes, which permits the determination of a wide range of copper and mercury ions concentrations. When the sample-selected volumes are 100 and 1000 μl the analytical ranges were 5.0 up to 500.0 μg l⁻¹ and 2.5 up to 30.0 μg l⁻¹ for Cu(II) and Hg(II) ions, respectively. Under these conditions, the detection limit was estimated as 0.63 and 0.25 μg l⁻¹ for copper and mercury ions determination. The system consumes 2 mg of Chelex 100 resin beads, 0.20 mg of APDC or 1.25 mg of Dithizone per determination and the traditional organic solvent extraction methodology, normally used in connection with APDC and Dithizone reagents, is not used here which permits to classify the present method as green.     

Simultaneous Production of Amyloglucosidase and Exo-Polygalacturonase by <Emphasis Type="Italic">Aspergillus niger</Emphasis> in a Rotating Drum Reactor

Simultaneous production of amyloglucosidase (AMG) and exo-polygalacturonase (exo-PG) was carried out by Aspergillus niger in substrate of defatted rice bran in a rotating drum bioreactor (RDB) and studied by a 3¹ × 2² factorial experimental design. Variables under study were A. niger strains (A. niger NRRL 3122 and A. niger t0005/007-2), types of inoculum (spore suspension and fermented bran), and types of inducer (starch, pectin, and a mix of both). Solid-state fermentation process (SSF) was conducted at 30 °C under 60-vvm aeration for 96 h in a pilot scale. Production of AMG and exo-PG was significantly affected by the fungal strain and the type of inoculum, but inducers did not trigger any significant effect, an evidence of the fact that these enzymes are constitutive. The maximum activity of exo-PG was 84 U g_dm ^?1 whereas the maximum yield of AMG was 886.25 U g_dm ^?1.     

Acuminatanol, the first 2′,2?-bis-dihydrobiflavonol from the aqueous extract of Trichoscypha acuminata

One new 3′,4′,5′,5,7-pentahydroxy-2′,2?-bis-dihydrobiflavonol, acuminatanol (1), was obtained from the aqueous extract of Trichoscypha acuminata. The structure elucidation process was performed primarily utilizing a capillary scale NMR probe. Acuminatanol (1) is the first example of a bis-dihydroflavonol linked exclusively via the B-rings at C-2′ and C-2? positions. To date, it is the first naturally-occurring compound reported from the genus Trichoscypha, and the first new natural product published from our compound libraries generated from the aqueous extracts of American and African plants.