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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Spas D. Kolev

Abbrev:
Kolev, S.D.
Other Names:
Address:
Department of Chemistry, Centre for Scientific Instrumentation, La Trobe University, Bundoora, Vic. 3083, Australia
Phone:
+61-3-9479-3747
Fax:
+61-3-9479-1399

Citations 17

"On-line Determination Of Mercury(II) By Membrane Separation Flow Injection Analysis"
Talanta 2004 Volume 63, Issue 4 Pages 1069-1075
Nazanin Amini, Terence J. Cardwell, Robert W. Cattrall, Richard J. S. Morrison and Spas D. Kolev

Abstract: A rapid and inexpensive gas-diffusion (GD) flow injection method for the on-line determination of Hg(II) in aqueous samples is described. The analytical procedure involves the injection of a Hg(II) sample into a 1.5 M H2SO4 carrier stream which is merged with a reagent stream containing 0.6% SnCl2 and 1.5 M H2SO4. Under these conditions Hg(II) is reduced to metallic mercury which partially evaporates through a Teflon membrane into an acceptor stream containing 1.75 x 10^-4 M KMnO4 in 0.3 M H2SO4. The decrease in the absorbance of the acceptor stream at 528 nm corresponding to the absorption maximum of the permanganate anion can be related to the original concentration of Hg(II) in the sample. The method is characterized by a detection limit of 4 µg L-1 and a sampling frequency of 8 h-1. The flow system was successfully applied to the analysis of river samples spiked with Hg(II).

"Determination Of Carbon Dioxide In Gaseous Samples By Gas Diffusion-flow Injection"
Talanta 2004 Volume 62, Issue 3 Pages 631-636
Sakchai Satienperakul, Terence J. Cardwell, Robert W. Cattrall, Ian D. McKelvie, Douglas M. Taylor and Spas D. Kolev

Abstract: A gas diffusion-flow injection system was developed for the determination of carbon dioxide in gaseous samples. The calibration was based on the use of either gaseous carbon dioxide or aqueous sodium carbonate standards. Gaseous carbon dioxide samples and gaseous or aqueous standards were injected directly into a donor stream of 1.0 x 10^-4 M H2SO4. In the gas diffusion unit, carbon dioxide diffused through a PTFE membrane into an acceptor stream containing a mixed acid/base indicator. The absorbance of the acceptor stream was monitored spectrophotometrically at 554 nm. The calibration plot was linear over the range of 5.00 x 102 to 1.27 x 104 µl L-1 with a sample throughput of 28 h-1 and 3.2% RSD ([CO2]=2.37 x 103 µl l-1, n=12). The detection limit was determined as 2.50 x 102 µl l-1. The flow system was successfully applied to the analysis of several natural gaseous samples and the headspace of milk containers during storage. The flow injection results were found to be statistically indistinguishable at the 95% confidence level from those obtained by gas chromatography using thermal conductivity detection.

"An Optical Membrane Redox Chemical Sensor For The Determination Of Ascorbic Acid"
Lab. Rob. Autom. 2000 Volume 12, Issue 4 Pages 200-204
Damien T. Newcombe, Terence J. Cardwell, Robert W. Cattrall, Spas D. Kolev

Abstract: The redox indicator, ferroin, tris(1,10-phenanthroline)iron(II) was incorporated into the perfluorosulfonated cation-exchange membrane Nafion and, together with optical fibers, a photodiode, and a light-emitting diode, was used for the construction of a redox optical sensor (optode). The optode was incorporated in the flow-through cell of a computer-controlled sequential injection (SI) system and used for the determination of ascorbic acid (vitamin C). A linear relationship between the logarithm of the ascorbic acid concentration and the membrane absorbance was obtained for the concentration range from 2.50 x 10^-3 to 1.00 x 10^-1 mol L-1 and a sample frequency of 17 h-1. The concentration of ascorbic acid determined in a number of commercial pharmaceutical products agreed well with iodometric titration results. This result shows that the SI system incorporating the ferroin/Nafion optode is suitable for the automated analysis of ascorbic acid in pharmaceutical products.

"Study Of The Reduction Of 1-(2 -pyridylazo)-2-naphthol In Ethanol-water Solutions"
Electroanalysis 2000 Volume 12, Issue 11 Pages 841-845
Spas D. Kolev, Lilibeth dlC. Coo, Terence J. Cardwell, Robert W. Cattrall

Abstract: The reduction of the azo dye 1-(2-pyridylazo)-2-naphthol (PAN) to 1-(2-pyridylhydrazino)-2-naphthol in ethanol-water solutions at a glassy carbon electrode was studied chronoamperometrically. A mathematical model taking into account the three dimensional diffusion of these two species and the disproportionation reaction of 1-(2-pyridylhydrazino)-2-naphthol was developed and fitted to the experimental chronoamperograms. In this way the value of the kinetic rate constant of the disproportionation reaction was determined as 0.090 s-1, in ethanol-water solutions containing 40, 80, and 100% (v/v) ethanol, respectively It was found also that electrons were involved in the reduction of the azo group. The value of the PAN diffusion coefficient used in the model calculations was determined earlier by flow injection analysis (FIA). The combination of FIA and chronoamperometry offers new possibilities in studying electrode reactions.

"Gas-diffusion Flow Injection Determination Of Hg(II) With Chemiluminescence Detection"
Anal. Chim. Acta 2007 Volume 582, Issue 1 Pages 103-108
Nazanin Amini and Spas D. Kolev

Abstract: A gas-diffusion flow injection method for the chemiluminescence detection of Hg(II) based on the luminol-H2O2 reaction was developed. The analytical procedure involved the injection of Hg(II) samples and standards into a 1.50 M H2SO4 carrier stream, which was subsequently merged with a reagent stream of 0.60% (w/v) SnCl2 in 1.50 M H2SO4 to reduce Hg(II) to metallic Hg. The gas-diffusion cell was thermostated at 85°C to enhance the vaporisation of metallic Hg. Mercury vapor, transported across the Teflon membrane of the gas-diffusion cell into the acceptor stream containing 1.00 x 10^-4 M KMnO4 in 0.30 M H2SO4, was oxidized back to Hg(II). The acceptor stream was merged with a reagent stream containing 2.50 M H2O2 in deionised water and then the combined stream was merged with another reagent stream containing 7.50 x 10^-3 M luminol in 3.00 M NaOH at a confluence point opposite to the photomultiplier tube of the detection system. The chemiluminescence intensity of the luminol-H2O2 reaction was enhanced by the presence of Hg(II) in the acceptor stream. The corresponding increase was related to the original concentration of Hg(II) in the samples and standards. Under optimal conditions, the chemiluminescence gas-diffusion flow injection method was characterized by a linear calibration range between 1 ?g L-1 and 100 ?g L-1, a detection limit of 0.8 ?g L-1 and a sampling rate of 12 samples per hour. It was successfully applied to the determination of mercury in seawater and river samples. © 2006 Elsevier B.V. All rights reserved.

"Pervaporation-flow Injection Determination Of Arsenic Based On Hydride Generation And The Molybdenum Blue Reaction"
Anal. Chim. Acta 2001 Volume 445, Issue 2 Pages 229-238
Thusitha Rupasinghe, Terence J. Cardwell, Robert W. Cattrall, Maria D. Luque de Castro and Spas D. Kolev

Abstract: A pervaporation-flow injection system for the determination of As(V) by the molybdenum blue method is described. Samples containing As(V) were pretreated with KI and HCl prior to injection to reduce As(V) to As(III). As(Hl) samples were injected into a 0.5 M HNO3 stream and then mixed with a stream containing 0.5% sodium borohydride. The arsine generated was transported in the pervaporation unit across a semi-permeable membrane into a 1.97 x 10^-3 M I-3(-) acceptor solution where it was oxidized to As(V). The acceptor stream was merged with a reagent stream containing 0.01% SnCl2, 0.1% hydrazine sulfate and 0.5% ammonium molybdate thermostated at 70°C. The concentration of arsenomolybdenum blue was monitored photometrically at 840 run. The calibration graph is characterized by two linear ranges between 2.0 and 15 mg L-1 and 25 and 1000 µg L-1, a sampling frequency of 8 h-1 and a detection limit of 15 µg L-1. The presence of phosphate, Ni(II), Cu(II), and Fe(H) which normally interfere with arsenic in the molybdenum blue reaction or with atomic absorption spectrometry does not affect the analytical determination in this new method at concentrations up to 1000 mg L-1. The method was applied successfully to industrial effluents containing As in the concentration range from 15 to 250 µg l-(1). Very good agreement with hydride generation atomic absorption spectrometry was obtained.
Pervaporation Speciation Preconcentration

"Determination Of Phenol In Water By Pervaporation-flow Injection Analysis"
Anal. Chim. Acta 2000 Volume 419, Issue 1 Pages 9-16
Sami Y. Sheikheldin, Terence J. Cardwell, Robert W. Cattrall, Maria D. Luque de Castro and Spas D. Kolev

Abstract: A pervaporation-flow injection method for the determination of phenol in aqueous samples is described. The method involves sample injection into a concentrated sodium chloride (25 wt.%) donor stream at pH 2 and stopping the flow of the acceptor stream containing 0.1 M KNO3 and 0.01 M NaOH in the acceptor chamber of the pervaporation unit for 12 min. This period allows the completion of phenol transfer from the headspace of the donor chamber of the pervaporation unit through the membrane into the static solution in the acceptor chamber. After restarting the flow through the acceptor chamber the phenol concentration is detected amperometrically at a glassy carbon electrode set at +0.6 V. At 20°C the linear detection range was found to be 1-50 mg L-1 with RSD varying between 1 and 4% for n=3. The detection Limit and sample throughput were determined as 0.9 mg L-1 and 5 hr-1, respectively. Excellent agreement with the standard 4-aminoantipyrine (4-AAP) method was observed when validating the method with lake samples containing suspension and spiked with phenol.
Phenol Lake Amperometry Electrode Pervaporation Method comparison

"Pervaporation-flow Injection Determination Of Ammonia In The Presence Of Surfactants"
Anal. Chim. Acta 2000 Volume 416, Issue 2 Pages 177-184
Lijuan Wang, Terence J. Cardwell, Robert W. Cattrall, M. D. Luque de Castro and Spas D. Kolev

Abstract: A pervaporation flow injection method is described for the analysis of ammonia in complex matrices (e.g. in the presence of surfactants, solid particles). The donor solution is 1.0 mol L-1 NaOH while the acceptor solution contains mixed acid-base indicators cresol red and thymol blue. The color change resulting from the ammonia entering the acceptor stream in the pervaporation unit is monitored photometrically at 590 nm. The method is characterized by a linear calibration range between 0.2 and 20 mg L-1, sampling frequency of 11 h-1 and detection limit of 0.1 mg L-1. The presence of surfactants in high concentrations (1000 mg l-1) does not affect the analytical determination. The method was applied successfully to industrial effluents containing ammonia in the presence of surfactants, other organics and suspended solids.
Ammonia Industrial Spectrophotometry Pervaporation Interferences Surfactant Teflon membrane

"An Optical Redox Chemical Sensor Based On Ferroin Immobilised In A Nafion (R) Membrane"
Anal. Chim. Acta 1999 Volume 401, Issue 1-2 Pages 137-144
Damien T. Newcombe, Terence J. Cardwell, Robert W. Cattrall and Spas D. Kolev

Abstract: The redox indicator, Fenoin, tris(1,10-phenanthroline) iron(II) was successfully incorporated into the perfluorosulfonated ionomer membrane Nafion(R). The redox properties of the optode membrane were studied under batch and flow conditions using acidified bromate or cerium(IV) solutions as oxidants and ascorbic acid or sodium ascorbate solutions as reductants. The experiments under flow conditions were performed in a computer-controlled sequential flow injection system incorporating a flow-through measuring cell where the optode membrane was mounted. Optical fiber technology was used to monitor the membrane absorbance with time. Some loss of sensitivity was observed after a number of redox cycles of the optode membrane. This was attributed to the dissociation of the Ferroin in the presence of Hi ions that entered the optode membrane from the acidified oxidising solutions and to the formation of a binuclear Fe(III)/1,10-phenanthroline complex when Ferroin was oxidized. Both undesirable effects were suppressed by the addition of excess 1,10-phenanthroline to the membrane composition.
Ascorbic acid

"Online Determination Of Cyanide In The Presence Of Sulfide By Flow Injection With Pervaporation"
Anal. Chim. Acta 1999 Volume 390, Issue 1-3 Pages 133-139
Hermin Sulistyarti, Terence J. Cardwell, M. D. Luque de Castro and Spas D. Kolev

Abstract: A pervaporation-flow injection (PFI) method is described for the analysis of cyanide in the presence of sulfide. The interfering sulfide ion in the injected sample is precipitated online using an acidified lead nitrate reagent solution before the donor stream enters the pervaporation cell. Using amperometric detection at a silver electrode set at -50 mV (vs Ag/AgCl), linear calibration was obtained in the range 0.02-100.0 mg L-1 with a detection limit of 1.0 µg L-1. Sample throughput was of the order of 12-15 h-1. When the method was applied to the analysis of synthetic samples, there was no significant interference from sulfide at concentrations up to 50 mg L-1. Thiocyanate did not interfere at levels up to 1000 mg L-1. When applied to industrial samples containing sulfide and thiocyanate ions where the cyanide ions are predominantly complexed with various metal ions the PFI method was found to give results close to those obtained by standard distillation methods for weak acid dissociable (WAD) cyanide.
Pervaporation

"Determination Of The Diffusion Coefficient Of 1-(2-pyridylazo)-2-naphthol In Ethanol-water Solutions Using Flow Injection And Nuclear Magnetic Resonance Techniques"
Anal. Chim. Acta 1999 Volume 386, Issue 1-2 Pages 137-144
Lilibeth dlC. Coo, Maruse Sadek, Robert T. C. Brownlee, Terence J. Cardwell, Robert W. Cattrall and Spas D. Kolev

Abstract: The values of the diffusion coefficient of PAN (1-(2-pyridylazo)-2-naphthol) in various ethanol-water solutions at 298 K were determined using both flow injection (FI) and nuclear magnetic resonance (NMR) techniques. The transient FI concentration curves monitored by the detector were described by the axially dispersed plug flow model with an axial dispersion coefficient obeying Taylors theory. The diffusion coefficient of PAN determined in 40-100% (v/v) ethanol solutions in water by both curve-fitting and the statistical moments method varied in the range from 2.43 x 10^-10 to 8.31 x 10^-10 m2 s-1. As expected, the diffusion coefficient values obtained by curve-fitting were found to be more reliable. A pulsed field gradient (PFG) spin echo NMR experiment was also used to measure the diffusion coefficient of PAN in the same solutions. The NMR results were found to follow the same trend as the FI results though they were from 5% to 16% lower in value. This deviation was attributed to the association effects facilitated by the experimental conditions under which the NMR measurements were taking place, i.e. in quiet solutions and at considerably higher concentrations than those used by the FI technique. The diffusion coefficient of PAN in pure water was calculated as 2.21 x 10^-10 m2 s-1 by extrapolating the FI results to zero ethanol concentration. The results reported in the present investigation can be used for studying the electrochemical properties of PAN in ethanol-water solutions as well as for elucidating the sensing mechanism of an optode based on immobilization of PAN into Nafion membranes.
1-2-Pyridylazo-2-naphthol Spectrophotometry Diffusion coefficients

"Determination Of Cyanide As Tetracyanonickelate(II) By Flow Injection And Spectrophotometric Detection"
Anal. Chim. Acta 1997 Volume 357, Issue 1-2 Pages 103-109
Hermin Sulistyarti, Terence J. Cardwell and Spas D. Kolev,*

Abstract: A two channel gas diffusion flow injection (GDFI) system was utilized successfully for the quantitative determination of cyanide. The analytical procedure is based on the complexation reaction in the acceptor stream between nickel ions in ammoniacal solution and the cyanide ions formed as a result of the diffusion of hydrogen cyanide from the acidified donor stream where the sample is injected. The design and the chemical parameters of the GDFI system were optimized with respect to sensitivity and sampling rate. The interference effect of a number of frequently encountered chemical species on the analytical determination was investigated in real samples and methods for their removal were developed. When applied to real samples where the cyanide ions are predominantly complexed with various metal ions the GDFI method was found to give results close to those obtained by standard distillation methods for weak acid dissociable (WAD) cyanide.
Cyanide Spectrophotometry Complexation

"Mathematical Modeling Of Flow Injection Systems"
Anal. Chim. Acta 1995 Volume 308, Issue 1-3 Pages 36-66
Spas D. Kolev

Abstract: Existing mathematical models of flow injection manifolds were classified on the basis of the main principles on which they were constructed. The models were also compared with respect to their predictive power, the complexity of their mathematical treatment and the requirement for computation time when applied to single-line and conjugated two-line flow injection systems. The axially dispersed plug flow model was found to give an acceptable compromise between mathematical simplicity and precision.
Dispersion Modeling Plug flow Review Theory

"Mathematical Modeling Of A Flow Injection System With A Membrane Separation Module"
Anal. Chim. Acta 1992 Volume 268, Issue 1 Pages 7-27
Spas D. Kolev*, and Willem E. van der Linden

Abstract: The mathematical model developed takes into account the geometrical dimensions and dispersion properties of the main section of the manifold, the mass transfer in the chambers of the separation module and the thickness and diffusion coefficient of the membrane. The model was solved analytically by the Laplace transform technique, in which the equations reduce to ordinary linear differential equations of the second order (details given). Details are given of the experimental flow scheme, which incorporates a dialysis module, and the stimulus - response technique (Levenspiel and Bischoff, Adv. Chem. Eng., 1963, 4, 95) was used to identify the unknown parameters in the model under flow injection conditions. Three experimental series were run: one with a PTFE dialysis membrane impermeable to the KCl tracer; a second series with a Cuprophan membrane which was permeable to KCl; and the third series with water as carrier solution in the acceptor line and 1.6 mM KCl in the donor line. The response curves at the inlet and outlet of each channel were monitored at different flow rates. Applications include the optimization of sensitivity and sample throughput, and characterization and improvement of the membranes. A math. model for a flow injection system with a membrane separation module based on the axially dispersed plug flow model was developed. It takes into account the geometrical dimensions and dispersion properties of the main sections of the manifold, the mass transfer in the channels of the separation module, and the characteristics of the membrane (thickness and diffusion coefficient within it). The model was solved anal. in the Laplace domain. The inverse transformation was found to give satisfactory results for reactor Peclet nos. less than 120. Otherwise a numerical solution based on the implicit alternating-direction finite difference method was preferred. The adequacy of the model was confirmed experimental on a flow injection manifold with a parallel-plate dialysis module. The unknown flow and membrane parameters were determined by curve fitting. The membrane parameters were determined also by steady-state measurements. Fairly good agreement between the dynamic and steady-state results and with results given in the literature was observed, which, together with other experimental results, supported the validity of the model and showed that it can be used successfully for the math. description and optimization of flow injection systems with membrane separation modules. In this connection, the influence of the reactor parameters and the sample volume on the performance of such a system were investigated and conclusions for improving its sensitivity and sample throughput were drawn. Other possible applications of the model are in membrane technol. for characterizing of various membranes and in process engineering for investigating the mass transfer in different dialyzers.
Modeling Dispersion Diffusion coefficients Dialysis Plug flow Laplace Optimization

"Analysis Of Transient Laminar Mass Transfer In A Parallel-plate Dialyzer"
Anal. Chim. Acta 1992 Volume 257, Issue 2 Pages 331-342
Spas D. Kolev* and Willem E. van der Linden

Abstract: Mass transfer under laminar flow conditions is discussed on the basis of the Navier-Stokes equations and the axially dispersed plug-flow model. By fitting the data, relationships were derived for predicting the mass-transfer coefficient and the Peclet number in a parallel-plate laminar flow system with one impermeable wall and an opposite wall at which the concentration. is uniform. This single-stream relation can be utilized for calculating the mass-transfer coefficients in both channels of a co-current parallel-plate dialyzer. The Peclet number in the axially dispersed plug-flow model derived for a parallel-plate flow where both sides are impermeable gives better results when applied to the co-current dialyzer than the single-stream relationship. The results obtained allow the math. modeling of process and anal. flow-through manifolds incorporating a dialysis module.
Theory Laminar flow Dispersion Modeling Dialysis

"Influence Of The Main Parameters Of A Parallel-plate Dialyzer Under Laminar Flow Conditions"
Anal. Chim. Acta 1992 Volume 257, Issue 2 Pages 317-329
Spas D. Kolev* and Willem E. van der Linden

Abstract: A math. model describing the mass transfer in a parallel-plate dialyzer with cocurrent laminar flow in both channels based on the Navier-Stokes equations and Fick's 2nd law was developed. Numerical solutions are presented for pulse- and stepwise concentration. changes of the solute in one of the channels using the Laplace transform technique. By simulation the effect of the main design and operational parameters of the dialyzer and the most important phys. constants for the mass-transfer process were investigated. Conclusions with regard to optimum design and operation were drawn and some possibilities for simplifying the model were established.
Dialysis Modeling Theory Dispersion Laplace Optimization Laminar flow

"Solution Of Mathematical Models Of Flow Systems Used In Analytical Chemistry And Process Analysis In The Case Of Slug And Time Injection"
Anal. Chim. Acta 1990 Volume 229, Issue 1 Pages 183-189
Spas D. Kolev

Abstract: Simple relationships have been derived for reduction of the analytical solutions obtained when using distributed- and lumped-parameter models for slug and time injection to the solutions for step- or δ-function inputs. The relationships allow considerable simplification, and afford substantial economy in computational time if numerical integration is performed. The validity of the approach is demonstrated with hydraulic models frequently used in flow injection analysis and chromatography.
Timed injection Theory Modeling