Virtual instrumentation for electro–analytical measurements

This paper deals with some applications of Virtual Instrumentation to electroanalytical measurements. Virtual Instruments (VIs) are software programmes that simulate the external appearance and functions of a real instrument on the screen of a computer. In this work, programmes have been developed to control the potential of a working electrode (through a suitable potentiostat), acquire the current response, process the acquired current signal, and control a peristaltic pump and injection valve. The sequence of operations was controlled by the VI. The programmes developed have been applied to amperometric and voltammetric measurements in static and flowing solutions. The Vl package that has been used was Lab VIEW 4.0.1 from National Instruments

Effect of guar gum on the physicochemical, thermal, rheological and textural properties of green edam cheese

In attempts to produce a low-fat cheese with a rheology and texture similar to that of a full-fat cheese, guar gum (within 0.0025–0.01%; w/v, final concentration) was added to low-fat milk. The obtained cheeses were characterised regarding their physicochemical, thermal, rheological and textural properties. Control cheeses were also produced with low and full-fat milk. The physicochemical properties of the guar gum modified cheeses were similar to those of the low-fat control. No significant differences were detected in the thermal properties (concerning the enthalpy and profile of water desorption) among all types of cheeses. The rheological behaviour of the 0.0025% modified cheese was very similar to the full-fat control. Overall, no trend was observed in the texture profile (hardness, cohesiveness, gumminess and elasticity) of the modified cheeses versus guar gum concentration, as well as in comparison with the control groups, suggesting that none of the studied polysaccharide concentrations simulated the textural functions of fat in Edam cheese

Qualitative Evaluation of N-Way Model Matching Approaches

In product line engineering tasks, the need for merging models from different product variants emerges as the commonly used clone-and-own approach suffers from high maintenance costs in the long run. By identifying models with a high number of similarities we can merge them to one highly reusable model. This approach will increase the maintainability, and further expandability of the model. Already many works have been published aiming to solve this problem with different N-way model Matching approaches. However, there is lack of practical evidence that the published theories work as designed in real world cases. In this work, we will evaluate relevant published approaches and then attempt to integrate the most promising one in the product line analysis framework VARIOUS from Fraunhofer IESE. Next, the implemented approach will be evaluated in comparison to the existing mechanism for model matching that VARIOUS integrates that is called "System Aligner". The main aspects of our evaluation are: • Accuracy - Can it accurately find the most similar models? • Performance - How fast is it? • Scalability - How well does it scale in large amount of input models? • Configurability - Can it be adapted easily for different systems

Determination of rutin and other flavonoids by flow-injection/adsorptive stripping voltammetry using nujol-graphite and diphenylether-graphite paste electrodes

The possibility of determination of twelve flavonoids (fisetin, galangin, hesperetin, hesperidin, kaempherol, morin, myricetin, naringin, quercetin, quercitrin, rutin, rhamnetin) using adsorptive stripping voltammetry in a flow injection system is examined. Carbon paste electrodes based on mixtures of nujol-graphite and diphenylether-graphite were used and compared as working electrodes and measurements were made using both 'direct' and 'medium-exchange' procedures. The effect of experimental parameters such as pH, accumulation potential and period, presence of various compounds was examined. Sample size (typically 0.33 ml) is greatly reduced by applying a reciprocating flow of the sample plug through the detector during the preconcentration step. The instrumental sensitivities and lower detection limits were calculated for all flavonoids in all cases. In some cases the differences are so high that determination of certain flavonoids in the presence of excess of others is allowed. Depending on the flavonoid, the electrode type, and the measurement procedure the analytical range and the reproducibility (RSD%) were 10-5-10-8 M and 2.5-10%, respectively. A simple procedure is developed for the electrochemical determination of rutin in a multivitamin preparation. (C) 2000 Elsevier Science B.V

Fast screening of total flavonols in wines, tea-infusions and tomato juice by flow injection/adsorptive stripping voltammetry

A novel approach for a fast screening of total flavonols (quercetin, kaempferol, myricetin) in wines, tea-infusions and tomato juice using adsorptive stripping voltammetry in a flow injection system is described. The proposed method is based on the property of flavonols to be pre-concentrated on carbon paste electrodes where diphenylether is used as the pasting liquid. The samples are subjected to an acid hydrolysis step and 1 mL sample of the diluted hydrolysate is injected in the flow injection apparatus. After 2 min pre-concentration period (under reciprocated flow) the electrode is washed with Britton-Robinson buffer, pH 5 solution and an anodic voltammetric scan is applied to produce an anodic current peak (analytical signal). The lower determination limits for kaempferol, quercetin and myricetin in pure aqueous solutions were 20, 9 and 25 μg L-1. Mixtures of flavonols resulted into a single anodic peak, which can be used for the calculation of the total flavonols concentration expressed in terms of "quercetin equivalent". The measurement throughput was about 13 h-1 and the overall reproducibility of measurements was 3-6%. The total concentration of quercetin equivalent in eight tested samples was found in the range 3-60 mg L-1 and the results compare favorably with those obtained by an LC procedure. © 2005 Elsevier B.V. All rights reserved

Virtual instrumentation for electro-analytical measurements

This paper deals with some applications of Virtual Instrumentation to electroanalytical measurements. Virtual Instruments (VIs) are software programmes that simulate the external appearance and functions of a real instrument on the screen of a computer. In this work, programmes have been developed to control the potential of a working electrode (through a suitable potentiostat), acquire the current response, process the acquired current signal, and control a peristaltic pump and injection valve. The sequence of operations was controlled by the VI. The programmes developed have been applied to amperometric and voltammetric measurements in static and flowing solutions. The VI package that has been used was LabVIEW 4.0.1 from National Instruments

Electrochemical Oxidation of Rutin

An electrochemical investigation of rutin oxidation on a glassy carbon electrode was carried out using cyclic voltammetry, differential pulse voltammetry and square-wave voltammetry over a wide pH interval. The electrochemical oxidation is a complex process, which proceeds in a cascade mechanism, related with the 4-hydroxyl groups of the rutin molecule. The catechol 3prime,4prime-dihydroxyl group is the first to be oxidized by a two-electron - two-proton reversible oxidation reaction, followed by an irreversible oxidation reaction due to the 5,7-dihydroxyl group. Both mechanisms are pH dependent. An adsorption process is also observed and the oxidation products block the electrode surface