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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Celio Pasquini

Abbrev:
Pasquini, C.
Other Names:
Address:
Instituto de Química, Universidade Estadual de Campinas, CP: 6154 CEP: 13083-970 Campinas SP, Brazil
Phone:
+55-19-3788-3136
Fax:
+55-19-3788-3023

Citations 16

"Effect Of Ethanol In The Organic Phase On Liquid-liquid Extraction In Monosegmented Flow Analysis. Determination Of Zinc In Drugs"
Talanta 2002 Volume 56, Issue 4 Pages 643-653
Emerson Vidal de Aquino, Jarbas José Rodrigues Rohwedder, Ileana Facchin and Celio Pasquini

Abstract: In liquid-liquid extraction performed by monosegmented flow analysis (MSFA), the aqueous sample is introduced between two air bubbles and flows, under restricted dispersion, through a glass extraction tube where the analyte is retained, usually at pH higher than 8. The retained analyte is removed to a small volume of an organic phase containing a ligand which is introduced after the second air bubble. In this work, the effect of the organic phase composition on the extraction of Cu(II), Zn(II) and Cd(II) in MSFA systems was investigated by changing the ethanol content (0.1-4% v/v) in toluene, chloroform and carbon tetrachloride. The extracting efficiency of the organic phases containing ethanol was evaluated by using dithizone (DT), 1-2-pyridylazo-2 naphthol (PAN) and sodium diethyldithiocarbamate (DDTC) as ligands for the metals. The MSFA extraction system was improved by introducing a new syringe-based device for organic phase delivery. The presence of ethanol in the organic phase shows a remarkable (up to ten times) effect on the extraction efficiency of the flow system when DT is employed. Its presence is mandatory if DDTC is used, as it accounts for ligand solubility in the organic phase. The extraction efficiency also increases with the pH of the aqueous phase as a consequence of higher ionisation of the glass silanols, where the analytes are adsorbed before extraction. The system has been evaluated for determination of Zn(II) in drugs showing a mean RSD of 2.2% and mean relative accuracy of 4.4%, when compared with atomic absorption spectrometry results. Typical sample frequency, sample and organic phase consumption are 30 samples per hour, 200 and 100 µl, respectively.

"Determination Of Water In Ethanol And Acetone By Direct Injection Enthalpimetry Based On The Heat Of Dilution"
Talanta 1984 Volume 31, Issue 1 Pages 82-84
Walace A. De Oliveira and Celio Pasquini

Abstract: Two analytical procedures based on the magnitude of the heat of dilution and direct injection enthalpimetry have been developed for determination of water in ethanol and acetone. The results obtained by means of the heat of dilution were compared with the values given by pycnometry, and gave a relative difference in the range 0.2-3%. The precision depends on the slope of the calibration curve, which varies with the procedure and the concentration of the sample.
Water Organic compound Organic compound Industrial Enthalpimetry

"Direct Reading Of Signals Obtained In Flow Injection Analysis"
Quim. Nova 1982 Volume 5, Issue 2 Pages 51-53
Pasquini, C.;De Oliveira, W.A.;Pasquini, C.

Abstract: A method is described for the direct reading of signals obtained in flow injection analysis which did not depend on the use of a microprocessor but was of simple low-cost construction. Experiments were made with K2Cr2O7 solutions in which routine absorption readings were made at 372 nm with a spectrophotometer, and 240 signals could be obtained per h.
Dichromate Chromium(VI) Spectrophotometry Apparatus

"Flow System For Pre-concentration And Spectrophotometric Determination Of Reactive Mercury"
J. Braz. Chem. Soc. 2005 Volume 16, Issue 5 Pages 928-935
Fernando S. Yonehara; Celio Pasquini*; Jarbas J. R. Rohwedder

Abstract: A new flow system to pre-concentrate and determine reactive mercury in effluents by photometry is presented. The system is based on the reduction of the reactive mercury present in a 500 mL sample with a Sn(II) solution. The reduced mercury is swept out by an argon stream and carried to a straight glass tube (60 cm long, 3 mm i.d.) inclined in an angle of 15o. The inner surface of this tube has been previously covered by a renewable liquid layer of an oxidant solution containing H2O2 (12%, m/v) and HNO3 (3.0 mol L-1) produced after introduction and passage of a liquid monosegment containing those reagents. The swept Hg0 undergoes an oxidative process and the Hg(II) formed is retained in the layer. After a 10 min sweep time interval the argon flow is stopped and a reagent monosegment (350 µL) containing PAR [4-(2-pyridylazo)resorcinol], 1.0 x 10^-3 mol L-1, in an ammonia/ammonium chloride buffer (4.0 mol L -1; pH 9.0) is introduced and passes through the glass tube. A strongly colored complex between PAR and Hg(II) is formed and carried to the detection system composed of a light emitting diode (LED, ?max = 525 nm) and a photodiode detector. Sample processing time is about 12 min. The system is washed and a fresh liquid layer is formed, preparing the system for a new determination. This method concentrates the sample by a factor of 148 and achieves a detection limit of 0.16 ?g L-1. ©2005 Sociedade Brasileira de Qui?mica.

"Gran Method For End Point Anticipation In Monosegmented Flow Titration"
J. Braz. Chem. Soc. 2004 Volume 15, Issue 1 Pages 111-115
Aquino, Emerson V; Pasquini, Celio; Rohwedder, Jarbas J. R; Raimundo Jr, Ivo M; Montenegro, M. Conceição B. S. M; Araújo, Alberto N

Abstract: An automatic potentiometric monosegmented flow titration procedure based on Gran linearisation approach has been developed. The controlling program can estimate the end point of the titration after the addition of three or four aliquots of titrant. Alternatively, the end point can be determined by the second derivative procedure. In this case, additional volumes of titrant are added until the vicinity of the end point and three points before and after the stoichiometric point are used for end point calculation. The performance of the system was assessed by the determination of chloride in isotonic beverages and parenteral solutions. The system employs a tubular Ag2S/AgCl indicator electrode. A typical titration, performed according to the IUPAC definition, requires only 60 µL of sample and about the same volume of titrant (AgNO3) solution. A complete titration can be carried out in 1-5 min. The accuracy and precision (relative standard deviation of ten replicates) are 2% and 1% for the Gran and 1% and 0.5% for the Gran/derivative end point determination procedures, respectively. The proposed system reduces the time to perform a titration, ensuring low sample and reagent consumption, and full automatic sampling and titrant addition in a calibration-free titration protocol.

"Adaptation Of A Cold Vapor Mercury Analyzer To Flow Injection Analysis"
J. Autom. Methods Manag. Chem. 1988 Volume 10, Issue 4 Pages 188-191
CELIO PASQUINI, WILSON F. JARDIM, and LOURIVAL C. DE FARIA

Abstract: A Coleman MAS-50A Mercury Analyser system was modified to allow the determination of Hg by flow injection analysis. Samples were digested either by the conventional EPA method or by a simplified procedure involving addition of concentrated HNO3 - H2SO4 (1:1), cooling to room temperature and addition of 6% KMnO4 solution before analysis within 15 min. A sample was mixed with carrier solution (1% HNO3 solution) and then with a 35% (w/v) solution (10% solution for EPA digestion procedure) of SnCl2 in 1% HNO3, before stripping of Hg from the aqueous solution with N (200 mL min-1). The mixture then passed to a gas - liquid separation cell (illustrated) and thence to the detector. The calibration graph was rectilinear for up to 25 µg of Hg. Average recovery of Hg was 96%. Results agreed with those obtained by the EPA procedure.
Mercury Industrial Spectrophotometry Sample preparation Method comparison Optimization Phase separator

"Mechanical Removal Of The Central Sample Zone To Avoid Air Bubbles In Nonsegmented Continuous-flow Analysis"
Anal. Chem. 1986 Volume 58, Issue 11 Pages 2346-2348
Celio Pasquini

Abstract: Two manifolds are proposed for substitution of the membrane air permeation cell used in the method described by Pasquini and De Oliveira (cf. Anal. Abstr., 1986, 48, 7J13). A fixed volume is removed from the central part of the monosegmented sample at the end of the incubation coil and introduced into the detector line, while the remainder of the solution and air bubbles pass to waste. The method is demonstrated by the spectrophotometric determination of NH3. Reproducibility is within <1%, response is rectilinear from 0.05 to 0.7 µg mL-1 and the detection limit is 5 ng mL-1.
Ammonia Spectrophotometry Debubbler Zone sampling

"Monosegmented System For Continuous-flow Analysis. Spectrophotometric Determination Of Chromium(VI), Ammonia And Phosphorus"
Anal. Chem. 1985 Volume 57, Issue 13 Pages 2575-2579
Celio Pasquini and Walace A. De Oliveira

Abstract: The system described is based on established flow injection analysis apparatus, into which the sample is introduced into the flow manifold between two air bubbles. The bubbles are removed with a permeation membrane before the stream reaches the detector. The characteristics of the system, evaluated in the absence of reactions, showed that the approach can be used for analytical methods requiring long residence times. In the spectrophotometric determination of NH3, P and Cr(VI) the detection limits were 5, 20 and 3 ng mL-1, respectively, at the 99.7% confidence level. The precision was better than 1%, and samples could be introduced at 120 h-1. The system can replace the classical segmented continuous-flow analysis or flow injection analysis methods, with improved sampling rate, sensitivity, and reagent and sample consumption.
Chromium(VI) Ammonia Phosphorus Spectrophotometry Membrane

"Flow System For Liquid-solid Extraction And Pre-concentration Using A Renewable Extracting Solid Phase"
Anal. Chim. Acta 2002 Volume 472, Issue 1-2 Pages 141-146
Angelo Capri Neto and Celio Pasquini

Abstract: A mechanised flow system is described aimed at extracting and pre-concentrating metal ions in a renewable water-insoluble solid phase containing a suitable ligand. The main difference between the proposed system and previously described ones for use with liquid-solid extraction is in the renewable characteristics of the solid phase, which allows for refreshing the extracting surface to be employed between pre-concentration operations. The renewable feature imposes no demands in terms of reversibility of the adsorption process as all the solid organic phase containing the complexed metal is dissolved by a non-aqueous solvent and carried to the detection system. Simultaneously, the system promotes a better compromise between metal extraction and pre-concentration as lower solvent volumes can be used to recover the absorbed species. The system has been evaluated for Zn(II) extraction in order to optimise its main geometrical and chemical variables. A simple spectrophotometric detection system employing a light emitting diode (LED) and a silicon photodiode was employed in these studies. Concentration gains of 42 and detection limits below 1.0 µg L-1 were obtained. Sample throughput and sample consume depend on the desired pre-concentration. For higher (>40) concentration factors, about 40 mL of aqueous sample and a total processing time of 20 min per sample are required.

"Monosegmented Flow Titrator"
Anal. Chim. Acta 2001 Volume 438, Issue 1-2 Pages 67-74
Emerson Vidal de Aquino, Jarbas J. R. Rohwedder and Celio Pasquini

Abstract: An automatic titrator based on the monosegmented flow approach is described. The flow titrator is unique in fulfils the definition of IUPAC for the titration technique. This means that, the flow analyzer. produces a complete titration curve and is capable using the equivalence point concept for determination of the titrant concentration without the use of any calibration, usually employed in similar systems. The titrant is added to the sample monosegment by using a syringe driven by a step motor. The titrant is added with a precision of±0.5 µl. The main advantage of the proposed flow titrator is in the fact that, if necessary, only one aliquot (100-200 µl) of the sample need be employed to make a complete titration with a suitable titrant solution. This feature has been demonstrated by titrating Fe(II) and H2O2 solutions with KMnO4. However, a complete titration is not the fastest way to find the end point. A successive approximations algorithm is described which allows the end point to be achieved in, at most, eight steps. The novelty of this approach is that the sample solution does not need to be discarded when titrant addition do not exceed the end point. The proposed flow titrator has been evaluated for spectrophotometric, indicator based, titrations of strong and weak acids and for titration of hydrogen peroxide in commercial products using KMnO4. The results show that the system can, on average, perform one titration each 2 min, when employing the successive approximations algorithm. The precision and accuracy for HCl or acetic acid titrations (concentration range 0.0025-0.100 mol l-1), using phenolphthalein as indicator, and H2O2, using the self indicating KMnO4 titrant, was from 0.5 to 2%. Because the proposed system resembles a real titrator in all aspects, all detection techniques employed for conventional titrations can be, in principle, also employed with this flow manifold.

"Determination Of Carbon Dioxide In Gaseous Samples Using A Monosegmented Flow System And Conductimetric Detection"
Anal. Chim. Acta 1998 Volume 366, Issue 1-3 Pages 223-229
Maria do Carmo Hespanhol da Silva, Jarbas Jos&eacute; Rodrigues Rohwedder and Celio Pasquini*

Abstract: The monosegmented approach to flow analysis was employed for determination of low contents (100-1000 ppmv) of CO2 in gaseous samples. The front bubble of the flow pattern constitutes the gaseous sample. The sample is pumped through a glass tube (2 mm i.d., 80 cm long) by deionised water. The film of water present in the tube wall absorbs the CO2 present in the sample. The liquid monosegment collects, by convection movement of the fluid, the layer containing the partially ionized CO2, while the second bubble restricts the dispersion of the collected specimens. The conductivity of the liquid monosegment is monitored at the end of the glass tubing and is proportional to the CO2 content in the gaseous sample. The system has been optimized for determination of CO2 in the 50-1000 ppmv range. For the experiment, 100 µL of sample is employed and the system can perform 60 determination per hour. The relative standard deviation for the signals of standards in the 100-900 ppmv range was ~3%. Comparison with a gas chromatographic method revealed a mean relative difference of 7% for samples containing CO2 in the 20-700 ppmv range. The system employing conductimetric detection does not employ any reagent, is very simple and suitable for field monitoring of CO2 present in the atmosphere, indoors and outdoors.
Carbon dioxide Gas Conductometry

"Determination Of Gaseous Species By Monosegmented Flow Systems. Volumetric Determination Of Oxygen And Carbon Dioxide"
Anal. Chim. Acta 1997 Volume 349, Issue 1-3 Pages 377-384
Maria do Carmo Hespanhol da Silva and Celio Pasquini*

Abstract: A Monosegmented Flow System was developed to determine the content of gaseous analytes in gaseous samples. The proposed system, in contrast with previous monosegmented systems, employs the gas bubbles as gaseous samples. The volume of the bubbles is assessed indirectly by counting the time elapsed by the passage (at constant flow rate) of the liquid-gas and gas-liquid boundaries, defined for each bubble, through optical switches. Two optical switches are employed for bubble volume measurement: one counts the bubble passage before analyte absorption and the other is positioned after the inlet point of the reagent (added only into the liquid monosegment) and, therefore, can assess the bubble volume after the analyte absorption. The ratio of the elapsed time intervals taken before and after the analyte absorption is used as analytical parameter and inversely related with the content of the gaseous analyte. The instrument is controlled by a micro-computer. The principle has been applied to the determination of O2 and CO2 (including when they are present in mixtures containing both specimens) in gaseous samples together with an inert gas. The results show a mean absolute error of 0.1% and 0.3% for determination of O2 and CO2 present in the range 5-50% and 5-15% (v/v), respectively, when calibration with standard gaseous mixtures is employed. An alternative procedure that employs the volume ratio directly as the volumetric fraction of the gaseous species in the sample was also evaluated. About 40 samples can be processed per hour with the proposed system.
Oxygen Carbon dioxide

"Two-phase Liquid-liquid Extraction In Monosegmented Flow Analysis. Determination Of Cadmium With 1-(2'-pyridylazo)naphthol"
Anal. Chim. Acta 1995 Volume 308, Issue 1-3 Pages 231-237
Ileana Facchin and Celio Pasquini*

Abstract: A monosegmented flow system was developed for liquid-liquid extraction. Monosegmented aqueous samples were introduced into a glass tube (50 cm x 2 mm i.d.) between two 50 µL air bubbles. The organic phase containing the extraction reagent was introduced after the second air bubble. The transfer of the analyte from the aqueous to the organic phase was achieved by adsorption on the inner walls of the tube followed by desorption into the organic phase. Flow rates of typically 1.2 ml/min were used. The detection assembly was attached to the glass tube and consisted of a green light emitting diode (λmax = 560 nm) and a light dependent resistor. The system was evaluated for the extraction of Cd(II) of pH 9.9 with 0.05% 1-(2'-pyridylazo)naphthol in CHCl3. Volumes of 200 µL were used for both the aqueous and organic phases and the extraction path length (i.e. distance to detector) was 45 cm. A linear calibration graph was obtained for up to 2 mg/l Cd(II) and the detection limit was 85 ng/ml. The extraction efficiency was ~e;75% and was improved to near 100% by changing the direction of the carrier flow a number of times during each extraction. The same methodology can be employed to extract Cu(II) and Zn(II). The sampling rate was 30 samples/h.
Cadmium(2+) Copper(II) Zinc(II) Spectrophotometry Sample preparation Air segmentation Complexation Extraction Light emitting diode Organic solvent Photodiode

"Single-phase Liquid-liquid Extraction In Mono-segmented Continuous-flow Systems"
Anal. Chim. Acta 1994 Volume 285, Issue 3 Pages 287-292
Ileana Facchin, Jos&eacute; W. Martins, Patr&iacute;cio G. P. Zamora and Celio Pasquini*

Abstract: The method depends on mixing an aqueous sample solution, an immiscible reagent solution and a common solvent for the other two phases. Reaction occurs rapidly in the single phase, which is then air-segmented and carried to a confluence with an aqueous solution, causing separation of the reagent phase for subsequent spectrophotometric measurement. The method was illustrated by the extraction of Fe(III). The sample solution was mixed with 50 mM thenoyltrifluoroacetone solution in isobutyl methyl ketone and with ethanol in a mixing chamber. The single-phase solution passed through a debubbler, then through a loop, where it was segmented between two air bubbles. A water stream carried the segment to a junction with saturated NaNO3 solution and phase separation occurred in an inverted U-tube. The complex in the organic phase was detected with light from a light-emitting diode (560 nm) passing through the liquid to a light-dependent resistor, which formed one arm of a wheatstone bridge. Calibration graphs were linear for 2-30 mg/l of Fe(III). The RSD was 1.5% (n = 10) for 10 mg/l. The results were similar to those obtained by manual extraction. Up to 80 samples/h could be processed.
Iron(III) Spectrophotometry Sample preparation Light emitting diode Segmented flow Method comparison Organic phase detection Debubbler Solvent extraction

"Flow System For Liquid Sample Introduction In Arc-spark Excitation Sources"
Analyst 1996 Volume 121, Issue 12 Pages 1923-1927
Carlos Roberto Bellato and Celio Pasquini

Abstract: A flow system, based on the monosegmented flow analysis approach, is described for the automated delivery of liquid samples to arc/spark excitation sources commonly used with plane grating spectrographs. The sample (50 µL) was carried between two air segments into the path of the excitation source via a hole drilled in a conventional graphite electrode. The arc/spark is applied to excite the sample for a pre-set time interval and the light emitted is integrated. A diagram of the flow system is given. The throughput was 25 samples/h. The flow system was used in the determination of Al, Pb and mixtures of Hf and Zr in aqueous solution (results presented and discussed).
Aluminum Lead Hafnium Zirconium Spectrophotometry Interface

"A New Approach To Flow-batch Titration. A Monosegmented Flow Titrator With Coulometric Reagent Generation And Potentiometric Or Biamperometric Detection"
Anal. Bioanal. Chem. 2006 Volume 386, Issue 6 Pages 1921-1930
Emerson Vidal de Aquino, Jarbas Jos&eacute; Rodrigues Rohwedder and Celio Pasquini

Abstract: Monosegmented flow analysis (MSFA) has been used as a flow-batch system to produce a simple, robust, and mechanized titrator that enables true titrations to be performed without the use of standards. This paper also introduces the use of coulometry with monosegmented titration by proposing a versatile flow cell. Coulometric generation of the titrand is attractive for titrations performed in monosegmented systems, because the reagent can be added without increasing the volume of sample injected. Also, biamperomeric and potentiometric detection of titration end-points can increase the versatility of the monosegmented titrator. The cell integrates coulometric generation of the titrand with detection of end-point by potentiometry or biamperometry. The resulting titrator is a flow-batch system in which the liquid monosegment, constrained by the interfaces of the gaseous carrier stream, plays the role of a sample of known volume to be titrated. The system has been used for determination of ascorbic acid, by coulometric generation of I2 with biamperometric detection, and for determination of Fe(II), by coulometric generation of Ce(IV) with potentiometric detection of the end-point, both in feed supplements. © Springer-Verlag 2006.