A membraneless gas-diffusion unit-multisyringe flow injection spectrophotometric method for ammonium determination in untreated environmental samples

A new design of a membraneless gas-diffusion (MGD) unit coupled to a multisyringe flow injection system is proposed. The spectrophotometric determination of ammonium using an acid-base indicator was chosen to show the feasibility of this approach. Hence, in alkaline medium, ammonium ions are transformed into ammonia (donor channel) which diffuses through the headspace into the acceptor stream (bromothymol blue solution), causing a pH change and subsequently a colour change. The exploitation of the enhanced potentialities of this re-designed MGD device was the main purpose of the present work. Hence, several strategies concerning flow management were studied seeking to characterize and improve the analytical features of the methodology and moreover, untreated environmental samples were analysed without previous filtration. Consequently, stopped flow in acceptor channel with continuous flow in donor channel was chosen for the application to wastewater and spiked river water samples. A linear concentration range between 10.0 and 50.0 mg L⁻¹ of NH₄⁺, a limit of detection of 2.20 mg L⁻¹ and a determination frequency of 11 h⁻¹ were obtained.     

Electrochemical Determination of Norepinephrine on Cathodically Pretreated Poly(1,5‐diaminonaphthalene) Modified Electrode

A sensitive and simple electrochemical method for norepinephrine (NE) determination was developed based on a poly(1,5‐diaminonaphthalene) film electrode (PDAN). Cathodically pretreated PDAN presents good selectivity, sensitivity, and reproducibility for NE. The polymer film can be easily electropolymerized onto a platinum electrode by cyclic voltammetry in 1.0 M HClO₄. A cathodic pretreatment, consisting of the application of a potential of ?0.7 V for 3 s (vs. Ag/AgCl) to PDAN before each voltammetric measurement, enhanced the electrochemical activity of NE with no inference of ascorbic acid (AA). In optimized conditions, PDAN presents linear responses for NE in the range of 9.90 to 90.9 µM by differential pulse voltammetry (DPV) with a detection limit of 1.82 µM. A relative standard deviation of 3.0 % was obtained for 10 consecutive measurements of 40.0 µM NE solutions. The cathodically pretreated PDAN was successfully applied for NE determination in pharmaceutical formulation samples.     

Experimental generation of high-contrast Talbot images with an ultrashort laser pulse

A femtosecond Ti:sapphire laser oscillator emitting pulses with 800 nm central wavelength, 10.9 fs pulse width, and 75 MHz repetition rate, combined with a dispersion-compensated diffractive system, was used to implement a large-area, high-contrast, broadband optical interference technique based on the Talbot effect. Chromatic artifacts associated with the huge spectrum of the optical source (approximately 150 nm) are compensated for with an air-separated hybrid diffractive-refractive lens doublet. The spatial resolution of the chromatically compensated Talbot images under femtosecond illumination is nearly identical to that achieved under continuous wave monochromatic illumination. Furthermore, the temporal width of the signal at the Talbot planes is limited by the group-delay-dispersion coefficient which is shown to be small. High-contrast one-dimensional periodic structures of 96.1 μm spacing generated by Talbot diffractometry are experimentally demonstrated.     

The Effects of Grape Polysaccharides Extracted from Grape By-Products on the Chemical Composition and Sensory Characteristics of White Wines

There is an increasing interest in the valorization of wine waste by-products. Grape pomace/marc can be an important source of polyphenols but also of polysaccharides (PSs). Therefore, the aim of this work was to extract PSs from grape pomace and musts and incorporate them into wines to improve their quality and valorize these residues. Two white wines were elaborated and treated with four different PS extracts obtained from white grape pomace, white must, a wine purified extract rich in RG-II, and commercial inactivated yeasts. In general, the use of grape PSs extracted from grape pomace or must improve some characteristics of wine, increasing the polysaccharide and volatile concentrations. These PS extracts can be useful to modulate some taste attributes such as an excess of acidity and bitterness and can also prevent the loss of volatile compounds associated with fruity and floral notes over time. This is the first study that shows the effects of grape polysaccharides on the chemical composition and sensory characteristics of white wines. Considering the obtained results, the grape pomace and surplus of musts can be considered valuable sources to obtain polysaccharide-rich products, opening a new opportunity to take advantage of by-products from the wine industry.