University of North Florida
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Contact Info

Stuart Chalk, Ph.D.
Department of Chemistry
University of North Florida
Phone: 1-904-620-1938
Fax: 1-904-620-3535
Email: schalk@unf.edu
Website: @unf

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Adelio A. S. C. Machado

Abbrev:
Machado, A.A.S.C.
Other Names:
Adélio A. S. C. Machado
Address:
LAQUIPAI, Faculdade de Ciências, R. Campo Alegre 687, Porto P4150, Portuga
Phone:
+351 2 6082874
Fax:
+351 2 6082959

Citations 5

"Urea Potentiometric Biosensor Based On Urease Immobilized On Chitosan Membranes"
Talanta 1998 Volume 47, Issue 1 Pages 183-191
Júlia M. C. S. Magalhães and Adélio A. S. C. Machado*

Abstract: Potentiometric biosensors based on urease (E.C. 3.5.1.5.) immobilized on chitosan membranes coupled to all-solid-state nonactin ammonium ion selective electrodes are described.:The enzyme was immobilized on the chitosan membranes by four procedures: (A) adsorption; (B) adsorption followed by reticulation with dilute aqueous glutaraldehyde solution;
Urea Potentiometry Sensor Electrode Chitosan

"Comparison Of The Simplex And Powell Methods With A Weighted Response Function For The Optimization Of FIA Systems"
Talanta 1993 Volume 40, Issue 7 Pages 1113-1126
L. M. B. C. Álvares-Ribeiro and A. A. S. C. Machado*J. Alonso, J. Bartroli and M. del Valle,

Abstract: The cited optimization methods were compared with regard to the determination of nitrite in water by flow injection spectrophotometry based on the method of Nakashima et al, (Anal. Chim. Acta, 1974, 155, 263). Both methods proved to be effective for the optimization, neither having any definite advantages over the other. The use of a weighted response function in the optimization methods was useful in assessing the versatility of flow injection systems.
Nitrite Water Optimization Powell Simplex

"Use Of A Linear Function Of Several Variables In Simplex Optimization As A Procedure For Assessing Analytical Versatility In FIA"
J. Chemom. 1988 Volume 3, Issue S1 Pages 249-256
Alonso, J. Bartroli, M. del Valle, A. A. S. C. Machado, L. M. A. Ribeiro

Abstract: The simplex optimization procedure described previously (Anal. Lett., 1987, 20, 1247) was used in conjunction with a linear response function involving sensitivity (peak height) and sampling rate (residence time, which should be minimized) to optimize a flow injection system similar to that of Nakashima et al. (cf. Anal. Abstr., 1984, 46, 7H41) for the determination of NO2- in water. It is concluded that sampling rates can be more than doubled compared with those of Nakashima et al. when analyzing residual waters containing >10 ppb of NO2-.
Nitrite Environmental Optimization Simplex

"Usefulness Of A Ruggedness Test In The Validation Of Flow Injection Analysis Systems"
Anal. Chim. Acta 1997 Volume 355, Issue 2-3 Pages 195-201
Luis M. B. C. Álvares-Ribeiro and Adélio A. S. C. Machado*

Abstract: The usefulness of a ruggedness test to evaluate the influence of small variations in the parameters fixed in the assemblage of a flow injection analysis (FIA) system on its response is presented. The purpose of the tested system was the determination of calcium in water with increased sensitivity by differential potentiometry involving two identical calcium ion selective electrodes. Youden and Steiner's ruggedness test was found to be a useful technique to ascertain that the optimized system worked properly.

"Optimization Of A Bipotentiometric Flow Injection Analysis System For Simultaneous Determination Of Calcium And Chloride Ions In Natural Waters"
Analyst 1998 Volume 123, Issue 4 Pages 653-659
Luis M. B. C. Álvares-Ribeiro and Adélio A. S. C. Machado

Abstract: Experimental optimization using the modified simplex method of a bipotentiometric flow injection analysis (FIA) system, constituted by two different ion selective electrodes (ISE) placed in series, for the simultaneous determination of Ca2+ and Cl- in water is reported. The response function used was a weighted linear combination of three variables, chosen to achieve maximization of the Ca2+ electrode sensitivity, minimization of the interference of the Ca2+ signal on the Cl- response, and maximization of the sampling rate. The optimized system can determine Ca2+ from 5 x 10^-5 to 5 x 10^-3 mol/L with a sensitivity of ~27 mV/decade and Cl- from 2 x 10^-4 to 2 x 10^-2 mol/L (the max. value tested), with a sensitivity of ~55 mV/decade. Repeatability was 1.9 and 0.6%, respectively, at 2 x 10^-4 and 2.2 x 10^-3 mol/L (8 and 90 mg/L), for Ca2+ determinations, and 1.8 and 1.2%, respectively, at 3.4 x 10^-4 and 8.3 x 10^-4 mol/L (12 and 29 mg/L), for Cl- determinations A sampling rate of 40/h was obtained. The affect of ionic strength on the results is discussed. The relative accuracy of the bipotentiometric FIA system was demonstrated by determining the content of both ions in natural water in parallel with ASTM certified methods.
Calcium Chloride Environmental Bipotentiometry Electrode Electrode Simplex Optimization Standard method Method comparison Interferences