The fast response double buck DC-DC converter (FRDB): operation and output filter influence

The fast response double buck (FRDB) dc-dc converter was presented like a low output voltage dc-dc converter with fast transient response, in order to feed devices such as microprocessors and digital signal processors (DSPs). The topology of the FRDB is composed of two buck converters connected in parallel, each one of them with different features and aims, and controlled by means of the novel linear-non-linear (LnL) control. In this paper, the topology, the control strategy and the operation principle are shown. Finally, experimental results in different prototypes are presented to show both, the transient response and the recovery time when these prototypes are subjected to load current steps, and the influence of the output filter on these parameters.     

Determination of Allura Red and Tartrazine in Food Samples by Sequential Injection Analysis Combined with Voltammetric Detection at Antimony Film Electrode

An antimony film electrode prepared on‐line and installed as part of a sequential injection system, was used as an electrochemical detector to determine azo dyes in food samples. The influence of several flow variables were evaluated using a central composite design. In optimal conditions, the linear range of the calibration curve varied from 1–5 µM, with a limit of detection limit of 0.3 µM. The relative standard deviation of analytical repeatability was <5.0 %.The method was validated by comparing the results obtained with those provided by HPLC; no significant difference were seen.     

PWM-PD multiple output DC/DC converters: operation and control-loop modeling

In this paper, PWM-PD multiple output dc/dc converters are presented. Operation analysis and power block design are shown. Furthermore, a small-signal model is developed for the PWM-PD multiple output dc/dc converters working in continuous conduction mode. The control-block is presented and the closed-loop circuit performances, such as the line, load and cross regulation, are obtained analytically. Finally, experimental results for a PWM-PD converter, with three fully regulated outputs and with transformer, are shown.     

Amperometric biosensor for oxalate determination in urine using sequential injection analysis

An amperometric flow biosensor for oxalate determination in urine samples after enzymatic reaction with oxalate oxidase immobilized on a modified magnetic solid is described. The solid was magnetically retained on the electrode surface of an electrode modified with Fe (III)-tris-(2-thiopyridone) borate placed into a sequential injection system preceding the amperometric detector. The variables involved in the system such as flow rate, aspired volumes (modified magnetic suspension and sample) and reaction coil length were evaluated using a Taguchi parameter design. Under optimal conditions, the calibration curve of oxalate was linear between 3.0-50.0 mg·L^-1, with a limit of detection of 1.0 mg·L^-1. The repeatability for a 30.0 mg·L^-1 oxalate solution was 0.7%. The method was validated by comparing the obtained results to those provided by the spectrophotometric method; no significant differences were observed.     

Determination of mineral balances in sheep offered feed with added cadmium and zinc

The optimum conditions for microwave digestion of herbage and faeces to determine mineral concentrations were obtained by varying sample mass, reagent and heating programme, and it was confirmed that the resulting element concentrations were the same as for certified reference material. The effects of feeding cadmium to sheep at a level that is typical of polluted regions (1 mg/kg) for ten days were investigated, as well as the possible amelioration of cadmium effects by adding 30 mg/kg Zn to the diet. Cadmium in the feed increased the cadmium balance and produced several mineral disturbances, in particular a reduction in sodium balance which is typical of renal tubular disorders. Including zinc in the diet as well as cadmium reduced the cadmium balance to a level similar to that of sheep that did not receive cadmium or zinc, which suggests that the zinc status is critical in determining whether cadmium in feed increases the cadmium balance in sheep.     

Determination of Piroxicam in Pharmaceutical Formulations Combining Amperometry and Multicommutation

This work describes the development of a multicommutated flow system with amperometric detection, applied in the determination of piroxicam in pharmaceutical formulations.     

High-performance liquid magneto-chromatography

High-performance liquid magneto-chromatography (HPLMC) is a new chromatography technique with two distinctive features: (a) a high surface area stationary phase with paramagnetic properties composed of magnetite embedded in a silica gel, and (b) a magnetic field (variable intensity 0-5.5 mT) that selectively retains paramagnetic substances in the stationary phase depending on their magnetic susceptibility. The system can also be used to separate diamagnetic compounds such as biologically active organic molecules, but these first need to be complexed with Fe and Cu compounds to render them paramagnetic. Herein, we describe the experimental setup and the relationship between the retention factor and the magnetic field intensity, i.e., the force interaction of the complexes in relation to the magnetized magnetite. The expression derived also provides the effective magnetic susceptibility (Deltachi) of the components separated.     

Determination of primary amino acids in wines by high performance liquid magneto-chromatography

Eight amino acids (ethanolamine, glycine, alanine, β-aminobutyric acid, leucine, methionine, histidine and asparagine) were identified and quantified in Spanish wines by high performance liquid magneto-chromatography (HPLMC) with UV-V spectrophotometry. For this method, the amino acids are first complexed with mono(1,10-phenanthroline)-Cu(II) to confer them paramagnetic properties, and then separated by application of a low magnetic field intensity (5.5 mT) to the stationary phase contained in the chromatographic column. Principal components analysis of the results obtained grouped together the wine samples according to their denomination of origin: “Ribera del Duero”, “Rueda” or “Rioja” (Spain). Through cluster analysis, a series of correlations was also observed among certain amino acids, and between these groupings and the type of wine. These clusters were found to reflect the role played by the amino acids as primary or secondary nutrients for the bacteria involved in alcoholic and malolactic fermentation.     

Polarographic determination of zirconium at trace level

An indirect polarographic method has been developed for the determination of zirconium by formation of molybdozirconophosphoric acid, its extraction with MIBK or a mixture of diethyl ether and 1-butanol, stripping with alkali and measurement of the Mo(VI) by its catalytic effect on the polarographic reduction of hydrogen peroxide. Depending on the extradant, a detection limit of 2.5 or 8.9 mu/gl, can be achieved.     

Dispersive solid-phase extraction based on butylamide silica for the determination of sulfamethoxazole in milk samples by capillary electrophoresis

A new method based on the combination of dispersive solid-phase extraction and capillary electrophoresis is proposed for the determination of sulfamethoxazole in milk samples. Butylamide silica was synthesized and used as extractant. Factors involved in sample treatment method such as: butylamide silica amount, NaOH concentration in methanol, sample volume, and dispersion time were evaluated using a Taguchi parameter design. Under optimal conditions, average recoveries ranged from 73 to 85% with a limit of detection of 0.05?mg?L^?1 were achieved. The proposed method is a useful technique for cleanup milk samples.