1,721,257 research outputs found
Analytical perspectives of taurine/graphite oxide electrode coatings
No full textSurface modifications of electrodes aimed at confering them appealing features, such as increased sensitivity and selectivity, still receive a continuously growing attention. Amongst the possible modifiers, are worth mentioning sulphonated species, such as Nafion, poly(p-aminobenzene sulfonic acid), cysteic acid, poly(p-toluene sulfonic acid) and so on [1]. All these species (except Nafion, that is directly casted onto the electrode) are deposited by electrochemical oxidation, either potentiostatically or by cyclic the potential in a wide range.
The applications of these sensors are quite widespread [1], spanning from inorganic ions to drugs, pharmaceuticals, herbicides, pollutants, biological fluids, etc.
In this contribution, a new type of modified electrode, based on the deposition of a taurine/graphite oxide film onto glassy carbon (GC) electrodes is proposed. The modification of the electrode is achieved by potentiostatic oxidation in a taurine solution using pH 7 phosphate buffer as supporting electrolyte.
The modified electrode presents attractive features, such as permselectivity against anions and preconcentration of cations, leading to substancially increased selectivity and sensibility with respect to bare GC electrodes.
The research is in progress, especially for evaluating possible applications to the analysis of species of alimentary concern in real samples. In fact, the permselectivity of the modifying layer should be particularly effective in avoid fouling and adsorption phenomena frequently seen in real matrices.
[1] E. Desimoni, B. Brunetti, Electroanalysis, 24, 2012, 1481-150
Comparing regression relationships: application to chemically modified electrodes
No full textWhen developing new chemically modified electrodes (CMEs), as currently
done in this laboratory, attention is always paid to carefully evaluate their
experimental performances [1-3]. This is especially needed after some
tentative modifications of experimental conditions. Comparing regression
relationships (RRs), usually obtained by ordinary least square regression,
may help in deciding the right direction towards the optimization of
electrode performances. This implies evaluating if significant differences
exist between slopes and/or intercepts of RRs, hence if experimental
differences arise only by inevitable random errors or not. In practice, the
necessary tests should allow verifying if the considered regression
relationships come from the same RRs population from which the actual
samples are drawn. It was suggested that such a kind of comparisons can be
performed by specific Student’s t-tests [4]. The flow chart for comparing
two RRs is presented in the figure.
H0: b1=b2
H0: not rejected H0: rejected
1 Compute common
slope
2 H0: a1=a2
END
H0: not rejected H0: rejected
1 Compute common END
regression relationship
2 END
(regression lines are significantly different)
(regression lines are parrallel)
Figure: Flow chart for the regression of two RRs; b: slopes; a: intercepts.
Comparing more that two RRs is also possible by similar tests [4]. The matter is presented with the help of specifically developed Mathcad worksheets. Some examples are described by using simulated results as well
as results relevant to CMEs developed in this laboratory.
[1] E. Desimoni, Analyst, 124 (1999) 1191-1196
[2] E. Desimoni, B. Brunetti, Anal. Chim. Acta, 655 (2009) 30-37
[3] E. Desimoni, B. Brunetti, Accred. Qual. Assur., 17 (2012) 635-637
[4] J.H. Zar, Biostatistical analysis, 5th Ed., Prentice Hall, Inc., Upper Saddle River, New Jersey, US, 201
Recent Advances in Electroanalysis of Vitamins
No full textVitamins are a chemically heterogeneous group of compounds known as essential for the normal functioning of the organic metabolism. Their decrease in humans can lead to several diseases and not being produced by the body, they need to be obtained from dietary sources or supplements. For these reasons, their determination in food, pharmaceutical and clinical samples is crucial. This article reviews key advances in electrochemical measurements of vitamins over the past decade. Particular attention is given to papers proving applicability to real samples analysis. The technical features of the proposed sensors are presented and discussed along with their analytical performances. Future trends and challenges are also addressed
About estimating the limit of detection of heteroscedastic analytical systems
No full textThe limit of detection is a fundamental figure of merit in chemical analysis. Many different approaches are available for its estimation, but only few allow analysing data characterized by a significant change of precision with concentration. Among these, the ISO 11843-2 approach is certainly the most suitable. However, its implementation may not look easy to operators needing to develop the necessary spreadsheets by commercial software packages. This paper is aimed to verifying if alternative approaches are available for getting acceptably approximate estimates of the LOD. Pragmatically, they were set-up by simply adapting some of the approaches already available in the literature, but compatible only with homoscedastic analytical systems. The results obtained by these alternative approaches when analysing a series of calibrations relevant to the electroanalytical determination of hexavalent chromium in some water samples were compared to those furnished by the ISO approach. The results allowed confirming the critical role of the numerosity of the available data on the consistency of any estimate. Even when using the ISO approach, reliable estimates were only obtained by performing a number of calibrations usually uncommon under standard routine conditions. In such a situation, the differences between the results obtained by all the examined approaches appear less important
Confronto di alcune linee guida internazionali per la verifica della conformità a normative legali o composizionali
No full textVoltammetric determination of Vitamin B6 in food samples and dietary supplements
No full textA simple and rapid voltammetric method based on the use of disposable screen-printed electrodes is proposed for the determination of vitamin B6. The influence of the pH on the voltammetric response was analyzed. Estimation of the linear range (2.0•10-6/7.2•10-5 M), calibration function, limit of detection (1.5•10-6 M) and reproducibility was performed along with the determination of possible interferences from species present in real samples. The proposed analytical system was successfully applied for the determination of pyridoxine in multivitamin supplements, energy drinks and breakfast cereals by using the standard addition method
Permselectivity and preconcentration properties of taurine/graphite oxide electrode coatings: Analytical perspectives
No full textA glassy carbon electrode is modified by the formation of a taurine/graphite oxide film. The procedure involves potentiostatic oxidation of taurine in a pH 7 solution. The modified electrode presents attractive features such as permselectivity against anions and preconcetration of cation species leading to an increased selectivity and sensibility respect to a bare electrode. Potential analytical applications are investigated
A new voltammetric sensor based on a glassy carbon electrode modified with 8-hydroxyquinoline-5-sulfonic acid
No full textAbout Acceptance and Rejection zones as defined in the EURACHEM/CITAC Guide (2007) “Use of uncertainty information in compliance assessment
No full textConsidering measurement uncertainty is mandatory in assessing conformance to legal or compositional limits, and specific guidelines are available issued by ASME, ISO and Eurachem/CITAC. However, differences between ISO and Eurachem/CITAC wordings could induce some perplexities in the most careful readers. Possible problems arise from considering that, before performing a test, it should be decided whether it is to be a test for conformity or a test for non-conformity. This choice could perhaps require some renaming of acceptance/rejection zones as defined in the Eurachem/CITAC Guide. A tentative solution is discussed in this contribution
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