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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Citations 24

"A Robust Multisyringe System For Process Flow Analysis. 1. Online Dilution And Single Point Titration Of Protolytes"
Analyst 1999 Volume 124, Issue 9 Pages 1373-1381
Fernando Albertús, Burkhard Horstkotte, Andreu Cladera and Víctor Cerdá

Abstract: A robust multichannel manifold involving a multisyringe piston pump used for performing process flow analysis is proposed. The simultaneous sequential determination of two analytes with a sampling frequency of 97 injections per hour is demonstrated. A robust and rapid continuous flow titration system, including a predilution step, was developed. A quantitative dilution, avoiding the need for diluting the standards too, is achieved in two steps by first splitting the concentrated sample stream and further dilution in a mixing chamber. A wide range of dilution grades (from 80 to 1150) can be easily implemented by software instructions, without the necessity of mechanical reconfiguration of the manifold. The resulting system gives medium or low dispersion peak signals with a sampling frequency of over 75 injections per hour for off-line diluted samples, and more than 33 injections per hour for concentrated samples. The proposed assemblage allows the automation of the single point flow injection titration procedure for the assay of acids and bases in concentrated process solutions. Recoveries of 97.5-103% were found with a maximum RSD value of 5%.
Sequential injection Simultaneous analysis Mixing chamber Dilution

"Non-linear Calibration In Single Point Flow Titration Of Protolytes - A Comparison Of Model Options By Using Delta Test"
Anal. Chim. Acta 2000 Volume 414, Issue 1-2 Pages 221-237
Fernando Albertús, Isel Cortés, Manuel Alvarez and Victor Cerda

Abstract: The complete description of the non-linear absorbance/concentration relationship obtained for systems used in single point photometric flow injection titrations of acids and bases is presented. The applicability of different models for fitting calibration data, as well as the more frequently used data processing options, are investigated under normal and restraining conditions by using experimental and simulated data sets. Theoretical and empirical models are examined in order to choose the simplest and the more efficient ones to provide good recoveries. The comparison among models is based on a novel statistical criterion (Delta Test) for contrasting the prediction efficiency by detecting systematic errors in estimated concentrations.
Spectrophotometry Theory Modeling Titrations

"An Automatic Titrator Based On A Multicommutated Unsegmented Flow System - Its Application To Acid-base Titrations"
Anal. Chim. Acta 2000 Volume 407, Issue 1-2 Pages 213-223
Cristina M. N. V. Almeida, Rui A. S. Lapa, José L. F. C. Lima, Elias A. G. Zagatto and M. C. U. Araújo

Abstract: A continuous flow methodology to perform acid-base titrations is described. The titrations are carried out on a multicommutated flow system which simulates batch titration procedures. The titration strategy is based on sequential insertion of increasing titrant and decreasing titrand volumes in a reactor, thus accomplishing complete titration curves. The assessment of the titration end point is similar to that of conventional batch procedures. The theoretical model for the determination of titrand concentration without requiring any calibration process is presented and discussed. The present system was evaluated in vinegar acidity determinations and provided an accuracy better than 3% with a good repeatability (relative standard deviation (RSD) = 2.5%; n = 10) and reproducibility (RSD < 5%). The titration accuracy is time-dependent and has been tested in the 2-10 min range.
Food Potentiometry Electrode Multicommutation Titrations Theory

"Single-point Titration. 4. Determination Of Acids And Bases With Flow Injection Analysis"
Anal. Chim. Acta 1979 Volume 105, Issue 1 Pages 67-75
Ove &Aring;str&ouml;m

Abstract: A single-point titrimetric system for acids and bases based on the flow injection principle is reported. The 30 µL sample is introduced into a water stream with a pneumatic injector; this stream is recorded potentiometrically with a glass electrode in a flow-through cell. The peak maxs. are a linear function of the acid or base concentration. in the range 0.01-0.1M. At a sampling rate of 180 samples/h, the relative deviation is <1%. The method can be used at sampling rates as high as 720 samples/h.
Potentiometry Electrode Titrations Buffer

"Comparison Of Merging Zones, Injection Of Reagent And Single Line Manifolds For Enthalpimetric Flow Injection Analysis"
Anal. Chim. Acta 1984 Volume 156, Issue 1 Pages 307-312
Celio Pasquini and Walace A. De Oliveira

Abstract: The flow enthalpimeter described can be used with any of the flow injection manifolds cited. Improved sensitivity and sampling rate are achieved by immersing the complete manifold (including the injection valve) in a constant-temperature bath and by using an open tube reactor (Schifreen et al., Anal. Abstr., 1979, 37, 3J177; 1978, 35, 1J25). The effects of flow parameters (viz, reaction-path length, flow rate and sample volume, etc.) on the over-all dispersion factor were investigated for all three manifold configurations listed for the determination of HCl by neutralization with NaOH. Limits of detection obtained with reversed-flow, single-line and merging-zone techniques were 0.07, 0.2 and 0.4 mM HCl, respectively, and sampling rates of 80 to 90 h-1 were possible.
Enthalpimetry Dispersion Heated reaction Merging zones Open tubular reactor Reverse

"Theoretical And Practical Aspects Of Acid-base Determinations By Spectrophotometric Flow Injection Analysis"
Anal. Chim. Acta 1988 Volume 206, Issue 1-2 Pages 333-337
Yecheskel Israel

Abstract: A simple mathematical treatment is applied to the instantaneous acid - base equilibria prevailing at the peak maxima for acid - base indicators when used as reagents in spectrophotometric flow injection determinations. Equations are derived relating the absorbance, the fraction of the relevant form of the indicator and the rate of change of either form with the initial concentration. of the analyte and other relevant parameters. Criteria are set for the choice of reagent/indicator combinations likely to yield rectilinear absorbance/concentration. dependence for general and special instances. Suitable conditions are described for the determination of HCl, H3PO4, acetic acid, NaOH and ethanolamine. Least-squares treatment of data yielded coefficient of variation of 0.5% over a reasonably wide concentration. range. The highest throughput of samples achieved was 144 h-1.
Spectrophotometry Theory

"Automatic Titrations In Unsegmented Flow Systems Based On Variable Flow-rate Patterns. 1. Principles And Applications To Acid-base Titrations"
Anal. Chim. Acta 1992 Volume 261, Issue 1-2 Pages 489-494
J. Marcos, A. &iacute;os and M. Valc&aacute;rcel*

Abstract: Automatic acid-base titrations were carried out by generating pH gradients in a continuous-flow manifold. A programmable, computer-controlled pump was used to produce variable, reproducible flow-rate patterns that were used to increase gradually the titrant concentration in the flow system. A colorimetric indicator reagent allowed the spectrophotometric detection of the equivalence point. Strong and weak acids, both alone and in mixtures, and two protons of the same acid were titrated with a relative standard deviation of 1.8%. The procedure was applied to the analysis of various real samples.
Titrations Flow rate variation

"Continuous-flow Titration System For The Generation Of Multivariate Spectrophotometric Data In The Study Of Acid-base Equilibria"
Anal. Chim. Acta 1995 Volume 312, Issue 2 Pages 189-198
J. Saurina, S. Hern&aacute;ndez-Cassou* and R. Tauler

Abstract: In the present work a continuous flow system to carry out spectrophotometric titrations is developed. The titrant solution is generated on-line from mixing two different stock buffer solutions. The composition of the titrant agent is sequentially varied along the titration by changing the ratio of flow rates of both buffer channels, and therefore the pH can be modified. One spectrum is recorded at each pH value when the absorbance achieves the steady state. The spectral data have been treated by means of a recently developed self-modelling multivariate curve resolution method (SPFAC procedure). This method has been applied to the study of the acid-base equilibria of 1,2-naphthoquinone-4-sulfonate (NQS). Four titrations with concentrations of NQS ranging from 1.6 x 10^-4 to 7.3 x 10^-4 M have been performed, and, in every case, 24 spectra at different pH have been registered. Three species are detected in the range of pH studied (6.9-12.3). Their distribution plot with pH and their unit spectrum have been obtained.
Spectrophotometry Titrations Equilibrium constants Multivariate calibration

"Selective Determination Of Protolytes By Flow Injection Analysis. A Guide For The Rational Selection Of Reagent Composition"
Anal. Chim. Acta 1997 Volume 344, Issue 3 Pages 271-280
Fernando Albert&uacute;s*, Isel Cort&eacute;s, Lars G. Danielsson and Folke Ingman

Abstract: The measurement of the concentration of a strong acid or base in the presence of a weaker one is described. A systematic methodology for selecting a reagent mixture for the spectrophotometric determination of protolytes by FIA is proposed. A theoretical study was performed of the instantaneous equilibria obtained at the peak maximum when two protolytes injected into the carrier merge and react with a buffer/indicator stream. The strength and concentration of the buffer required to neutralize the stronger component without reacting with the weaker one were deduced. Guidelines are given for the selection of an indicator for combination with a preselected buffer. Synthetic and real samples of acid and alkaline mixtures were analyzed and the results were compared with those obtained by potentiometric titration.
Spectrophotometry Potentiometry Buffer Titrations Method comparison

"Flow Injection System For The Rapid And Sensitive Assay Of Concentrated Aqueous Solutions Of Strong Acids And Bases"
Anal. Chem. 1985 Volume 57, Issue 2 Pages 563-564
John A. Polta, In-Hyeong Yeo, and Dennis C. Johnson

Abstract: A pulsed amperometric detection method is described for the frequent quality-control monitoring of production streams of high-purity acids and bases, especially for strong acids and bases for which H+-selective glass electrodes lack sensitivity. The measurement of a small difference in concentration. between the reference and an injected solution is preferable to the quantitative determination of that difference over an extended range of concentration. Alternatively, the sample solution can be pumped as the carrier stream with occasional injections of standard reference solution. The theory of the method, based on the measurement of change of anodic current at a platinum electrode, is given.
Water Amperometry Electrode Process control

"Sequential Determination Of Both Acids And Bases By Optosensing Flow Injection Analysis Using A Single-line Manifold"
Anal. Chem. 1987 Volume 59, Issue 23 Pages 2767-2773
Bruce A. Woods, Jaromir Ruzicka, and Gary D. Christian

Abstract: Dilute acids and bases were determined by single-point titration by injection of the sample (30 µL) into 0.1 M acetate buffer (pH 5.7) carrier stream followed by monitoring of the color change of an immobilized indicator (Colorphast, Merck) with use of an optical-fiber system (details given) in the same single-line manifold at the rate of 120 samples h-1. Plots of peak-height and peak-width measurements vs. concentration. gave rectilinear calibration graphs from 0.001 to 0.11M.
Spectrophotometry Optical fiber Immobilized reagent Optosensing Peak width Titrations

"A New Flow Injection Titration Analysis"
Fresenius J. Anal. Chem. 1988 Volume 330, Issue 6 Pages 484-488
Jun'ichi Toei

Abstract: The flow injection system consists of a multi-function pump, UV detector and sample syringe connected to a six-way injection valve with a loop containing a mixing chamber and attached reagent syringe. The sample and reagent can be stirred and the chamber volume can be varied between 15 and 150 µL. Results are reported of tests to determine reproducibility (coefficient of variation 2.0 to 2.5%) and the effects of carrier flow rate, reagent volume, carrier acidity, type of acid and sample concentration. on peak width and shape for the titration of NaOH (sample) with HCl, H2SO4 or acetic acid (carrier) with phenolphthalein as indicator (reagent). The sampling rate is 60 to 120 h-1 and the method is useful when the reagent is unstable, and for slow titration reactions.
Spectrophotometry Optimization Reactor Titrations Peak width

"Continuous Sample Monitoring By Flow-reversal Methodology"
Fresenius J. Anal. Chem. 1992 Volume 342, Issue 7 Pages 547-551
M. Romero-Salda&ntilde;a, A. R&iacute;os and M. Valc&aacute;rcel

Abstract: In the configuration proposed, the spectrophotometric detector was mounted in the loop of the injection valve. A single reversal of the flow direction, via a selecting valve, was activated when the detector signal fell to zero. Compared with the normal flow, peaks obtained by flow reversal were narrower and more Gaussian with lower dispersion. The influence of ionic strength, viscosity, surface tension and temperature on the dispersion were studied. Applications of the system, including acid - base titrations are described. A flow reversal methodology based on a single change of the flow direction was used for the continuous monitoring of samples injected into an unsegmented flow-system. The photometric detector was located in the loop of the injection valve and the flow was reversed once each whole plug emerged. Sample dispersion in the carrier stream was continuously monitored in systems with and without chemical reaction. The influence of various physicochem. variables was studied and some anal. possibilities are discussed.
Spectrophotometry Flow reversal Peak shape Dispersion Titrations Viscosity

"Flow Injection Analysis With Amperometric Detection For Measurements Of Proton Activities In Solutions Of Strong Acids And Strong Bases"
Fresenius J. Anal. Chem. 1997 Volume 357, Issue 4 Pages 392-396
Anastas Dimitrov Dakashev

Abstract: Flow injection and reversed flow injection analysis with amperometric detection were used for the determination of the concentrations of strong acids and strong bases and the pH of the solutions. The amperometric detection was based on the reduction current of hydrogen ion or water molecules. A platinum indicator electrode cathodically polarized at a constant potential was employed, choosing the potential in the rising part of the current/potential curve. On the basis of the experimental data an equation was developed for the calculation of the concentrations of the strong acids and strong bases and the pH by a non-linear regression computer program. Analysis was carried out with an FIA system (schematic given) consisting of a peristaltic pump and an injection valve with a loop volume of ~100 µL. An electrochemical detector as described previously (Ilcheva and Dakashev, Analyst, 1990, 115, 1247) was adapted to amperometric determination using a Pt wire (4 x 0.5 mm diameter) placed axially in a cylindrical channel (2 mm diameter) as an indicator electrode. An OH 102 polarograph was also used. A buffer vessel (75 ml) was inserted between the peristaltic pump and the injector valve. Buffer solutions were aqueous solutions of 0.1 M HCl/glycine for acid buffers and 0.1 M NaOH/glycine for basic. An equation was developed, using the data obtained by this system, to calculate concentrations of strong acids and bases, and pH, by a non-linear regression computer program (details given).
Amperometry Electrode Chemometrics Buffer Activity

"Flow Sorption Calorimetry, A Powerful Tool To Investigate The Acid-base Character Of Organic Polymer Surfaces"
Fresenius J. Anal. Chem. 1997 Volume 358, Issue 1-2 Pages 244-247
S. Schneider A, F. Simon A, D. Pleul A, H.-J. Jacobasch

Abstract: Flow sorption calorimetry (FSC) can be a useful tool to estimate the Lewis acid-base behavior of the surface of organic polymers with less than 1 m2/g surface area. Polyethylene powders grafted with different amounts of acrylic acid have been chosen as samples. The surface of the powders was investigated by means of X-ray photoelectron spectroscopy (XPS) at first and than brought into contact with the strong electron donor triethylamine in a special FSC measuring system. The heat of the displacement isotherm together with the surface excess isotherm of triethylamine adsorbed onto the powders was determined. The results obtained with FSC and XPS were well correlated and gave a comprehensive picture of the acidic surface character of modified polyethylene.
Calorimetry

"Studies On Peak Width Measurement-based Flow Injection Analysis Acid - Base Determinations"
Microchim. Acta 1985 Volume 87, Issue 1-2 Pages 49-64
Jae-Seong Rhee and Purnendu K. Dasgupta

Abstract: Peak width measurement was used to determine strong acids or bases by injection into an aqueous indicator flow stream and spectrophotometric measurement in a flow-through cell (8 or 75 µL volume) at 615 nm (bandwidth 4 nm). The parameters investigated included concentration. and pK of the indicator, dimensions of the dispersion tube, signal level used for peak width measurement, sample volume, carrier flow rate, viscosity of the carrier stream and the diffusion coefficient of the analyte. As an example, the use of bromothymol blue is illustrated.
Spectrophotometry Diffusion coefficients Gradient technique Speciation Titrations Peak width Viscosity

"Determination Of Acids, Bases, Metal Ions And Redox Species By Peak-width Measurement Flow Injection Analysis With Potentiometric, Conductometric, Fluorimetric And Spectrophotometric Detection"
Microchim. Acta 1985 Volume 87, Issue 1-2 Pages 107-122
Jae-Seong Rhee and Purnendu K. Dasgupta

Abstract: The concept described earlier (see preceding abstract) has been extended by using the cited detection modes. Thus, conductometric and potentiometric detection were used to determine strong acids and bases, fluorimetric detection for Al(III) (aqueous morin as carrier), and spectrophotometric detection for Fe(II) [K3Fe(CN)6 as carrier], Cu(II) (catechol violet as carrier), H2O2 (I- as carrier), and Na2S2O3 (I3- as carrier). Absolute calibration plots over a wide concentration. range were obtained by using a few dispersion measurements; precision was good.
Conductometry Fluorescence Potentiometry Spectrophotometry Gradient technique Peak width

"Flow Injection Analysis Of Concentrated Aqueous Solution Of Strong Acids And Bases"
Anal. Sci. 1985 Volume 1, Issue 5 Pages 481-482
T. IMATO and N. ISHIBASHI

Abstract: The sample solution (e.g., 7.32 M H2SO4 or 6.97 M NaOH) is injected into a carrier stream of water, which then merges with a stream of 3 M acetic acid - 3 M Na acetate containing 20 µM-methyl red. The absorbance change at 520 nm and the potential change of a glass electrode in the flow path are monitored. The peak heights are almost rectilinearly related to concentration. of H2SO4 up to 4 M or NaOH up to 7M, and the method is also applicable to H3PO4. For 7 M NaOH, the coefficient of variation was 0.8% (n = 10). The procedure can be used for intermittent analyzes or continuous monitoring.
Electrode Electrode

"Sequential Injection Acid-base Titration - A Useful Application For Process Analytical Science"
Anal. Commun. 1997 Volume 34, Issue 5 Pages 147-151
Jacobus F. van Staden and Hanneli du Plessis

Abstract: The method is based on sequential injection of base titrant, acid analyte and base titrant into a carrier stream of water, giving a stack of well-defined zones in the holding coil (4.8 m x 1.02 mm i.d.) prior to reversed flow-through a reaction coil to the detector. A diagram of the system is given. Bromothymol blue (0.0016%) was included in the base (NaOH) as indicator for detection at 620 nm. The optimal flow rate was 2.13 ml/min. The calibration graph was linear for 0.01-0.1 M HCl using 1 mM NaOH as titrant. The RSD were Only 700 µL base and 100 µL acid sample was required per analysis. A sequential injection (SI) titration system is proposed for the titration of a strong acid with a strong base. The concept is based on the sequential injection of a base titrant, acid analyte and a base titrant zone into a distilled water carrier stream, giving a stack of well-defined zones adjacent to each other in a holding coil, which is swept by reversal through a reaction coil to the detector. The base zones contain Bromothymol Blue as indicator and the endpoint was monitored spectrophotometrically at 620 nm. A linear relation between peak width and logarithm of acid concentration. was obtained in the range 0.01 to 0.1 mol L-1 of HCl with 1 x 10^-3 mol L-1 of NaOH as titrant. Other linear ranges are possible by changing the titrant concentrations. The results obtained of the sequential injection titration of samples is in good agreement with a standard potentiometric method with an relative standard deviation < 0.30%. The system is fully computerized with a sample frequency of 30 samples h-1.
Spectrophotometry Method comparison Sequential injection Titrations Process control

"Flow Injection Analysis: Potential For Process Composition Measurement"
InTech 1984 Volume 31, Issue 5 Pages 51-54
Mowery, R.A.

Abstract: A review is presented, with 16 references, in which sample dispersion and concentration. profiles are discussed and applications to redox and acid - base measurements are described.
Industrial Dispersion Review Redox Process control

"The Principles Of Flow Injection Analysis As Demonstrated By Three Lab Exercises"
J. Chem. Educ. 1979 Volume 56, Issue 10 Pages 677-680
Hansen, E. H.; Ruzicka, J.

Abstract: Three lab. experiments are described to illustrate a continuous-flow anal. technique, in which samples are injected into a continuously moving stream. The sample then mixes with and reacts with reagents in the stream (or added downstream) prior to its passage through a detecting device. Significant factors in this flow injection analysis technique are sample injection, reproducible timing, and controlled dispersion. The described experiments are for determination of chloride in water samples, determination of phosphate in output from a chromatography column, and titration of a strong acid with a strong base.
Water Spectrophotometry Education Review Titrations

"Flow Injection Analysis Of Acid And Base Using Thermo-sensitive Resistance Coils"
J. Flow Injection Anal. 1995 Volume 12, Issue 1 Pages 66-76
Kei TODA*, Senju IWATA, Isao SANEMASA and Toshio DEGUCHI

Abstract: A flow injection analysis of acid-base by detecting neutralization heat is proposed. A injected sample (acid or base), combined with a carrier (deionized water), was mixed with a reagent (base or acid) stream. A change in the solution temperature was detected by passing the solution, immediately after mixing, through a stainless steel capillary tube around which a thermo-sensitive resistance was coiled. The temperature of carrier was used as a reference. Hydrochloric acid solutions of 0.003 to 0.2 M could be determined at a rate of 120 samples/h. Using this system, determination in weak-acid and weak-base system could also be performed. Thermo-sensitive resistances used in this work were completely free from corrosion, and effects of the ambient temperature and the sample diffusion in the detector were minimized.
Thermistor Temperature

"Flow Injection Spectrophotometric Determination Of Acids And Bases"
Quim. Anal. 1994 Volume 13, Issue 4 Pages 200-205
Albertus, F.;Cortes, I.;Ingman, F.;Danielsson, L.G.

Abstract: A flow-injection system is described for the spectrophotometric determination of acids and bases. Sample was injected into a carrier stream of water (2.6 ml/min) which was merged with a stream containing buffer solution and indicator. After passing through a mixing coil (1 m x 0.5 mm i.d.) the absorbance of the resulting stream was measured. Results were calculated using a non-linear calibration method. A variety of buffer systems and indicators were investigated; results are tabulated. Measurements with RSD <2% were possible. Results were compared with those obtained using potentiometric titrimetry.
Environmental Spectrophotometry

"FIA Acid–base Titrations With A New Flow-through PH Detector"
Anal. Bioanal. Chem. 2005 Volume 382, Issue 8 Pages 1981-1986
H. Kahlert, J. R. P&ouml;rksen, J. Behnert and F. Scholz

Abstract: A pH-sensitive detector for flow-through potentiometry based on a graphite/quinhydrone composite electrode was applied for flow-injection analysis (FIA) titrations. Hydrochloric acid and acetic acid were titrated by injection of samples into a sodium hydroxide carrier solution. System conditions were optimized by variation of flow rate, injection volume and titrant concentration. The parameters sampling frequency, residence time and dispersion coefficient were determined. The evaluation of peak width (time between the two inflection points on each side of the peak), peak area and slope of the raising edge of the peak lead were studied with respect to their use for calibration. Hydrochloric acid and acetic acid could be titrated down to a concentration of 2 x 10^-4 mol L-1 using 150 µL injection volumes, which is almost ten times lower than can be achieved using color indicators and a spectrophotometric detection.
Electrode Peak width Dispersion Method comparison Optimization Titrations