University of North Florida
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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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Alberto N. Araujo

Abbrev:
Araujo, A.N.
Other Names:
Alberto N. Araújo, Alberto Nova Araújo
Address:
CEQUP/Departamento de Quimica-Fisica, Faculdade de Farmacia UP, Rua Anibal Cunha, 164, 4050 Porto, Portugal
Phone:
+351-2-208-7132
Fax:
+351-2-200-4427

Citations 15

"Colorimetric Determination Of Copper In Aqueous Samples Using A Flow Injection System With A Pre-concentration Poly(ethylenimine) Column"
Talanta 1999 Volume 50, Issue 2 Pages 337-343
Alberto N. Araújo, Rui C. C. Costa and Julian Alonso-Chamarro

Abstract: A colorimetric flow injection-system for the determination of Cu(II) in waters based on complexation reaction with 4-(2-pyridylazo)-resorcinol, usually termed PAR, is described. Performing measurements in 0.25 mol L-1 HNO3 medium allowed improved selectivity of the analytical method. The lack of sensitivity deriving from the low complex absorption under acidic conditions was balanced by the insertion of an immobilized poly(ethylenimine) (PEI) column where Cu(II) pre-concentration in neutral media occurs. Using sample volumes ranging from 2 to 4 ml, sampling rates of 24 and 12 samples h-1 within a detection limit of 25 and 13 µg L-1, respectively, were accomplished. Accuracy of the developed methodology was assessed by comparison with atomic absorption spectrometry being the relationship [FIA] mg L-1 = 1.00 (±0.03) x [AAS] mg L-1 + 0.00 (±0.02) obtained after analyzing 15 samples. Precision was also evaluated using two samples of 0.05 and 0.5 mg L-1 copper, and a relative standard deviation (RSD) better than 3% was attained for both.

"Amperometric Biosensor Based On Monoamine Oxidase (MAO) Immobilized In Sol-gel Film For Benzydamine Determination In Pharmaceuticals"
J. Pharm. Biomed. Anal. 2003 Volume 33, Issue 5 Pages 983-990
Djane S. de Jesus, Cristina M. C. M. Couto, Alberto N. Araújo and M. C. B. S. M. Montenegro

Abstract: The development and application of a flow-through amperometric biosensor for benzydamine determination in anti-inflammatory drugs is described. The biosensor was obtained by physical entrapment of monoamine oxidase in a sol-gel film applied on platinum or carbon paste conducting support. The sol-gel membranes were prepared using an optimum concentration of 3-aminopropyltriethoxy silane, 2-(3,4-epoxycyclohexyl)ethyl-trimethoxy silane, double distilled water saturated with polyethylene glycol 6000 and HCl. The developed biosensors were incorporated in a single channel flow injection system to enable the determination of benzydamine in the concentration range of 0.05-2.5 mmol L-1 (with platinum based electrode) or within 0.1-2.5 mmol L-1 (carbon paste based electrode). The operational stability of the bioanalytical system developed was about 3 months permitting approximately 4700 substrate measurements. The flow injection system developed enables a sampling rate of 20-25 samples h-1 and relative S.D. of results less than 4%. The analytical usefulness of the proposed procedure was evaluated through analysis of commercial pharmaceutical products containing benzydamine, available on the Portuguese market. The results obtained did not differ significantly from the values resulting from analysis of the same products by the method described in the BP Pharmacopoeia.

"Solid Phase Retention With Reversed Elution In A SIA System With Detection By Flame Atomic Absorption Spectrometry"
Can. J. Anal. Sci. Spectrosc. 2003 Volume 48, Issue 5 Pages 320-324
COSTA Rui C. C. ; ARAUJO Alberto N. ; MONTENEGRO M. Conceicao B. S. M. ; PIMENTEL M. Fernanda ; SILVA Valdinete L.

Abstract: The development of a pre-concentration procedure based on sequential injection analysis with flame atomic absorption spectrometry (SIA/FAAS) for the determination of Mn in water samples presenting a concentration between 4.50 and 200.0 ?g L-1 is described. Mn is retained on-line on a strong cationic resin (AG 50W-X8) and eluted under stopped-flow conditions with a chelating solution. Accuracy of the results attained was assessed by comparison with electro thermal atomic absorption spectrometry providing the relationship [SIA] ?g/L = 1.00 (±0.07)*[ETAAS]?g/L - 0.3 (± 7.6) after analysis of 10 samples. Evaluation of repeatability give a relative standard deviation of 2.9 and 1.8 % after ten replicate of two samples containing 108 and 166 ?g L-1 of Mn, respectively.
Manganese Water Spectrophotometry

"Sequential Preconcentration For The ETAAS Determination Of Pd In Human Urine"
Atom. Spectrosc. 2002 Volume 23, Issue 1 Pages 17-23
Costa, R.C.C.;Almeida, A.A.;Araujo, A.N.;Silva, V.L.

Abstract: A sequential injection analysis system for the determination of Pd in human urine by electrothermal atomic absorption spectrometry is described. The system runs fully independent of the autosampler of the equipment. The procedure is based on the retention of the complex formed between Pd and diethyldithiocarbamate on a column of silica C18 and elution with about 43 µL of ethanol directly into the graphite furnace. Using about 8 mL of sample resulted in a detection limit of 9 ng/L and a sampling rate of about 10 samples/h. Accuracy of the proposed methodology was evaluated by recoveries ranging between 91% and 100%. Repeatability assessed as %RSD in three samples with 26, 46, and 61 ng/L Pd concentration yielded 11.3, 5.8, and 4.8%, respectively.
Knotted reactor

"Sequential Injection Analysis Of Lead Using Time-based Colorimetric Detection And Preconcentration On An Anionic-Exchange Resin"
Anal. Sci. 2004 Volume 20, Issue 4 Pages 679-682
Nestor Zárate Aracama, Alberto N. Araújo And Ricardo Perez-olmos

Abstract: The development of a sequential injection analysis manifold for the colorimetric determination of lead in water samples is described. The concentration of lead was assessed from its catalytic effect on the reaction of resazurine reduction caused by sulfide in an alkali medium. To that effect, the reaction zone was stopped at the detector, and the time interval required for the attainment of an absorbance decrease of 0.800 at the wavelength of 610 nm was estimated. Interference of other transition metals of the samples was minimized by adding potassium iodide to the sample and retaining the iodocomplexes formed in an on-line anionic resin (AG1 X8). Elution was made with a 2 mol/L sodium hydroxide solution. The relationship [SIA] µg/L = 0.99 (±0.11) x [ETAAS] µg/L + 0 (±4) was obtained upon comparing the results given by the proposed system and by electrothermal atomization atomic absorption spectrometry (ETAAS) after the analysis of ten water samples.

"Application Of Sequential Injection Analysis To The Assay Of Lead Retention Characteristics By Poly(vinylpyrrolidone): Trace Analysis Of Lead In Waters"
Anal. Sci. 1999 Volume 15, Issue 10 Pages 991-994
Alberto N. Araújo, Rui Cerdeira C. Costa And José L. F. C. Lima

Abstract: This paper presents the use of poly(vinylpyrrolidone) (PVP), which is a low-cost polymer for lead pre-concentration in natural-water samples. The weak granular structure of this polymer imposed the use of a stainless-steel filter holder for its conditioning in a thin filtering layer. This unit was inserted into a sequential injection analysis system coupled to a flame atomic absorption spectrophotometer (SIA/FAAS). The developed system allows sampling rates of 16 samples/h with a 60-fold enrichment factor and a detection limit of less than 5 µg/l for a 13 mL sample volume. The performance of the present system was also assessed by carrying out recovery trials, which provided results of between 96% and 101%. The precision of the methodology developed has never been over 3% regarding RSD and 5% for the deviations to the conventional procedure.
Preconcentration Preconcentration Extraction

"Kinetic Determination Of Uric Acid In Urine Based On Single-line Flow-system With Multi-site Detection"
Anal. Sci. 1998 Volume 14, Issue 4 Pages 809-813
Alberto N. Araújo, José A. M. CATITA and José L. F. C. LIMA

Abstract: A flow injection system based on multi-site detection for kinetic spectrophotometric determination of uric acid in urine is described. The system was studied regarding phys. dispersion, elimination of sample matrix interferences and applicability to real samples. In the optimized system, the sample is inserted into a water stream which merged downstream with the reagent solution containing iron(II) chloride and TPTZ. This system enables the determination of about 30 samples/h, and yields precise results (RSD usually <2.9%). Sensitivity is 212 mAU l/mmol up to 0.60 mmol/l uric acid. Accuracy was assessed by running 32 samples already analyzed by a conventional enzymatic procedure. No statistical difference between methods was found at the 95% confidence level.
Uric acid Urine Kinetic Interferences Optimization Method comparison Multidetection

"Colorimetric Bismuth Determination In Pharmaceuticals Using A Xylenol Orange Sol-gel Sensor Coupled To A Multicommutated Flow System"
Anal. Chim. Acta 2004 Volume 504, Issue 2 Pages 235-241
Paula C. A. Jer&oacute;nimo, Alberto N. Ara&uacute;jo, M. Concei&ccedil;&atilde;o B. S. M. Montenegro, Dalibor Satinsk&yacute; and Petr Solich

Abstract: A new sol-gel Bi(III) sensor was developed by incorporating xylenol orange (XO) into sol-gel thin films (<1?m thick) coated on glass slides. Several sols were produced in order to evaluate the effect of different processing parameters on the final characteristics of the sensor. Sensor films based on tetramethoxysilane (TMOS) as precursor, nitric acid catalysis, water:alkoxide ratio of 2 and XO concentration of 1.5gl-1 were found to be the most suitable to be used as Bi(III) sensors. They presented good sensitivity, reversibility and stability, low leaching and fast response time in the proposed working conditions. These sensors were coupled to a multicommutated flow system for the determination of Bi(III) in pharmaceutical products. The absorbance of the Bi(III)-immobilized XO complex formed was monitored at 515 nm. The regeneration of the sensor was accomplished by flowing a Cl- ion solution through the flow cell containing the sensor membranes. The procedure enables a relative standard deviation of results better than 0.8%, an analytical concentration range between 125.0 and 875.0?gl-1, a detection limit of 7.0?gl-1 and a sampling frequency of 45 samples per hour. The results obtained on real samples analysis were compared with those obtained by EDTA titrimetric method (British Pharmacopoeia), with relative deviation errors inferior to 5%. © 2003 Elsevier B.V. All rights reserved.

"Determination Of Fe(III) And Total Fe In Wines By Sequential Injection Analysis And Flame Atomic Absorption Spectrometry"
Anal. Chim. Acta 2001 Volume 438, Issue 1-2 Pages 227-233
Rui Cerdeira de Campos Costa and Alberto Nova Ara&uacute;jo

Abstract: The sequential determination of Fe(III) and total Fe in Portuguese table wines by sequential injection analysis (SIA) with flame atomic absorption spectrometry (FAAS) at a sampling rate of 18 samples h-1 is described. The determination of Fe(m) is based on the extraction with MIBK of the complex formed between Fe(III) and thiocyanate by using an on-line device for gravimetric analysis previously described for FIA systems, as liquid-liquid extraction module for organic phases less dense than water Afterwards, the determination of total iron is accomplished by sending a small sample aliquot directly to the FAAS nebulizer. The injection of about 1.8 mL of sample enabled the determination of Fe(m) ranging between 0.10-6.00 mg L-1 The injection of sample volumes of 83, 125, or 333 µL enabled the determination of total iron contents ranging between 1.50-15.00, 0.50-10.00, or 0.25-5.00 mg L-1, respectively. The Linear regression analysis of the results obtained for the two parameters with the proposed procedure and those provided by the reference methods (colorimetry for Fe(III) and FAAS for total Fe) led to the following relationships: [SIA] = 0.05(±0.31) + 0.98(±0.10) x [colorimetric] for Fe(III) and [SIA] = -0.14(±0.29) + 1.03(±0.04) x [FAAS] for total Fe.

"Sequential Injection System In Flame Atomic Absorption Spectrometry For The Determination Of Calcium And Magnesium In Mineral Waters"
Anal. Chim. Acta 1998 Volume 358, Issue 2 Pages 111-119
Alberto N. Ara&uacute;jo,*, Rui C. C. Costa, Jos&eacute; L. F. C. Lima and Boaventura F. Reis

Abstract: A flow set-up based on sequential injection analysis is proposed to increase the versatility and robustness of routine flame atomic absorption anal. methods. Four procedures were selected to allow the determinations of Ca within 0.03-10.00 and 0.58-200.00 mg/L, and Mg within 0.03-1.5 and 0.80-50.0 mg/L in mineral waters. The sample aliquots inserted were 70.8 and 12 µL for Ca and 13 and 12 µL for Mg. The system enabled to restrict the consumption of the releasing agent to respectively. 142 and 97 µL in the determinations of Ca and to 26 and 12 µL in the determinations of Mg. The results of the analysis of 15 mineral waters were compared with those obtained by the corresponding conventional procedures. In all cases the sampling rates were >110/h, and reproducibility was better than 3.
Calcium Magnesium Mineral Spectrophotometry Sequential injection Method comparison

"Flow-through Sol-gel Optical Biosensor For The Colorimetric Determination Of Acetazolamide"
Analyst 2005 Volume 130, Issue 8 Pages 1190-1197
Paula C. A. Jer&oacute;nimo, Alberto N. Ara&uacute;jo, M. Concei&ccedil;&atilde;o B. S. M. Montenegro, Dalibor Satinsk&yacute; and Petr Solich

Abstract: An optical biosensor based on immobilized carbonic anhydrase and its application to the determination of the anti-glaucoma agent acetazolamide by enzyme inhibition measurements, is described. The enzyme and a pH indicator dye, cresol red, were physically immobilized in overlapped sol-gel thin films, in a dual-layer format. Carbonic anhydrase catalyses the dehydration of HCO 3-, which in turn causes a change of pH in the microenvironment of the sensor. By following the color transition of cresol red, the enzymatic reaction as well as its inhibition by acetazolamide can be monitored. The sensor was integrated in a flow cell and coupled to a continuous flow system operating on a multicommutation and binary sampling approach. Measurements were made at pH 6.0 at the wavelength of 570 nm. Linear response was obtained for acetazolamide concentrations between 1.0 and 10.0 mmol l -1, with a sampling frequency of 22 samples h-1 and a detection limit of 0.2 mmol l-1. The results obtained in the analysis of real samples were in good agreement with those obtained by a reference method, showing no significant differences at a confidence level of 95%. © The Royal Society of Chemistry 2005.

"Electrospray Ionization Mass Spectrometry Fingerprinting Of Beer"
Analyst 2005 Volume 130, Issue 6 Pages 884-889
Alexssander S. Ara&uacute;jo, Lilian L. da Rocha, Daniela M. Tomazela, Alexandra C. H. F. Sawaya, Reinaldo R. Almeida, Rodrigo R. Catharino and Marcos N. Eberlin

Abstract: After just simple degassing, dilution, pH adjustment and direct flow injection, characteristic fingerprint spectra of beer samples have been obtained by fast (few seconds) electrospray ionization mass spectrometry (ESI-MS) analysis in both the negative and positive ion modes. A total of 29 samples belonging to the two main beer types (lagers and ales) and several beer subtypes from USA, Europe and Brazil could be clearly divided into three groups both by simple visual inspection of their ESI(+)-MS and ESI(-)-MS fingerprints as well as by chemometric treatment of the MS data. Diagnostic ions with contrasting relative abundances in both the positive and negative ion modes allow classification of beers into three major types: P = pale (light) colored (pilsener, pale ale), D = dark colored (bock, stout, porter, mild ale) and M = malt beer. For M beers, samples of a dark and artificially sweetened caramel beer produced in Brazil and known as Malzbiers were used. ESI-MS/MS on these diagnostic beer cations and anions, most of which are characterized as arising from ionization of simple sugars, oligosaccharides, and iso-α-acids, yield characteristic tandem mass spectra adding a second and optional MS dimension for improved selectivity for beer characterization by fingerprinting. Direct ESI-MS or ESI-MS/MS analysis can therefore provide fast and reliable fingerprinting characterization of beers, distinguishing between types with different chemical compositions. Other unusual polar components, impurities or additives, as well as fermentation defects or degradation products, could eventually be detected, making the technique promising for beer quality control.

"Sequential Injection Analysis Of Free And Total Potassium In Wines Using Potentiometric Detection And Microwave Digestion"
Am. J. Enol. Vitic. 2003 Volume 54, Issue 1 Pages 46-49
N&eacute;stor Z&aacute;rate, Alberto N. Ara&uacute;jo, Maria Concei&ccedil;&atilde;o B.S.M. Montenegro, and Ricardo P&eacute;rez-Olmos

Abstract: An automatic procedure for the determination of free and total potassium in wines is described that combines sequential injection analysis with potentiometric detection. A sequential injection mounting is coupled to a microwave system to conduct the on-line digestion of the sample, thereby making the injection of samples possible without prior treatment. Free potassium was determined by injecting 110 µL of sample and forwarding it to the detection system. In the evaluation of total potassium, the sample was previously digested with 390 µL of hydrogen peroxide for 60 seconds at 700 W in a microwave oven. Using an optimized mounting, 10 samples of different wine types were analyzed (white, red, and port), and results were then compared with those provided by flame emission photometry. Relative standard deviations obtained were always below 3% and sampling rate attained was about 14 samples per hour.
Potassium Port Wine Wine Red Wine White Sample preparation Sample preparation Spectrophotometry Potentiometry Apparatus Automation

"Metals Determination In Wines By Sequential Injection Analysis With Flame Atomic Absorption Spectrometry"
Am. J. Enol. Vitic. 2000 Volume 51, Issue 2 Pages 131-136
Rui Cerdeira C. Costa, M. Isabel Cardoso, and Alberto N. Ara&uacute;jo

Abstract: This paper describes the application of sequential injection analysis with flame atomic absorption spectrophotometric detection (SIA/FAAS) for the determination of Zn, Mn, Fe, and Cu in Portuguese Verde, Maduro, and Porto wines. The basic configuration of the system allowed the determination of Zn, Mn, Fe, and Cu, the latter in concentrations higher than 0.20 mg/L. Selecting a sample volume of 340 µL allowed the determination of Zn and Mn up to 1.50 and 3.00 mg/L, respectively. The Fe determination was accomplished using 85, 120, and 340 µL sample volumes for Fe contents in the range of 1.50 to 15.00 mg/L, 0.50 - 10.00 mg/L, and 0.25 - 5.00 mg/L, respectively. Wine samples with Cu contents in the 0.20 to 2.00 mg/L range were analyzed with a sample volume of 750 µL. The determination of Cu trace levels was carried out using an heterogeneous-phase pre-concentration unit composed of a commercial cartridge packed with silica C18 coupled to the system. Cu was retained as diethylammonium-N,N-diethyldithiocarbamate chelate. Using about 2 mL of sample allowed determination of Cu between 0.05 and 0.50 mg/L. A comparison of the results obtained by the proposed methodologies and the reference procedures presented relative deviations less than 5%. Repeatability of determinations was always better than 3% (RSD).
Zinc Manganese Iron Copper Wine Spectrophotometry Sequential injection C18 Method comparison

"Direct Determination Of Copper In Urine Using A Sol–gel Optical Sensor Coupled To A Multicommutated Flow System"
Anal. Bioanal. Chem. 2004 Volume 380, Issue 1 Pages 108-114
Paula C. A. Jer&oacute;nimo, Alberto N. Ara&uacute;jo, M. Concei&ccedil;&atilde;o B. S. M. Montenegro, Celio Pasquini, Ivo M. Raimundo Jr

Abstract: In this work, a multicommutated flow system incorporating a sol-gel optical sensor is proposed for direct spectrophotometric determination of Cu(II) in urine. The optical sensor was developed by physical entrapment of 4-(2-pyridylazo)resorcinol (PAR) in sol-gel thin films by means of a base-catalyzed process. The immobilized PAR formed a red 2:1 complex with Cu(II) with maximum absorbance at 500 nm. Optical transduction was based on a dual-color light-emitting diode (LED) (green/red) light source and a photodiode detector. The sensor had optimum response and good selectivity towards Cu(II) at pH 7.0 and its regeneration was accomplished with picolinic acid. Linear response was obtained for Cu(II) concentrations between 5.0 and 80.0 µg L-1, with a detection limit of 3.0 µg L-1 and sampling frequency of 14 samples h-1. Interference from foreign ions was studied at a 10:1 (w/w) ion:Cu(II) ratio. Results obtained from analysis of urine samples were in very good agreement with those obtained by inductively coupled plasma mass spectrometry (ICP-MS); there was no significant differences at a confidence level of 95%.
Copper Copper(II) Urine Sensor Sol-gel Complexation Light emitting diode Photodiode Selectivity Linear dynamic range Detection limit Interferences Statistics