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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Adsorption

Classification: Parameter -> Adsorption

Citations 31

"Synthesis Of A New Chelating Resin Containing Nitrogen And Sulphur Donor Sites And Its Application For The Removal Of Inorganic Arsenic From Natural Water"
Indian J. Chem. A 2002 Volume 41, Issue 9 Pages 1821-1825
Mondal, Bhim Chandra; Das, Arabinda K

Abstract: Chloromethylated polystyrene divinyl benzene (3 %) has been functionalised through -NH-CH2- bond with bis-(2-aminophenyl)disulfide. The resulting chelating resin has been characterized by elemental analyzes, infrared spectra and metal ion capacity. The sorption capacities for both As(III) and As(V) have been determined using batch technique and they show a strong sorption at pH 4.5. The effect of the presence of co-existing ions have also been examined. The concentration of each of the arsenic species has been determined by HG-AAS. The sorption and desorption cycles have been examined using a column packed with the resin without any loss of column performance which indicates the possibility for its reuse. The developed column technique has been used for the removal of arsenic species from natural water.

"Adsorption Of Aqueous Inorganic Mercury And Methylmercury On Suspended Kaolin: Influence Of Sodium Chloride, Fulvic Acid And Particle Content"
Appl. Organomet. Chem. 2001 Volume 15, Issue 6 Pages 490-498
Alberto de Diego, Chun Mao Tseng, Nicolai Dimov, David Amouroux, Olivier F. X. Donard

Abstract: The main tendencies in the adsorption of dissolved inorganic mercury (Hg2+) and methyl-mercury (MeHg+) on suspended kaolin particles have been investigated in synthetic aqueous solutions. The influence of NaCl, fulvic acid (FA) and suspended particulate matter (SPM) in the system has been studied at a constant pH of 7.2, The experiments were arranged according to a full factorial design with three factors (NaCl, FA SPM) at low (-) and high (+) levels. A central point (0) was repeated four times to estimate the reproducibility of the results. The low and high levels investigated were 0-35 g L-1 0-10 mg L-1 and 0.5-5 g L-1 for the concentrations of NaCl, FA and kaolin respectively. In order to match the linear range of the analytical technique the total concentration of mercury (as Hg2+ or MeHg+) in the synthetic suspensions was 25 ng mi After chemical stabilization of each suspension, the Hg2+ or MeHg+ content in the clear filtrate was determined by an automated hyphenated technique combining the following steps: (i) derivatization by hydride generation, (ii) pre-concentration by cryogenic trapping, (iii) separation by packed column gas chromatography and (iv) detection by quartz furnace atomic absorption spectrometry, The removal of Hg2+ and MeHg+ from the solution via adsorption on particles ranged, respectively, from 12.4 to 94.9% and from 1.7 to 45.6% of the total mercury compound concentration, High concentrations of NaCl led to lower adsorption rates of both mercury species, The adsorption of MeHg+ was enhanced in the presence of FA, whereas that of Hg2+ was clearly diminished. High levels of SPM promoted the adsorption of both Hg2+ and MeHg+ on kaolin particles. Several experiments were also conducted to check the adsorption rate of Hg2+ and MeHg+ on natural particles collected in the Gironde estuary, The results confirmed the general trends observed when using reference kaolin particles, The results presented here will be helpful for groups modelling the physico-chemical behavior of mercury in estuary conditions.

"Disjoining Pressure Vs Thickness Isotherms Of Thin Emulsion Films Stabilized By Proteins"
Langmuir 2001 Volume 17, Issue 26 Pages 8069-8077
Tatiana D. Dimitrova, Fernando Leal-Calderon, Theodor D. Gurkov, and Bruce Campbell

Abstract: In the present paper, we report measurements of the disjoining pressure vs thickness isotherms of emulsion films stabilized by proteins. A novel variant of the Mysels-Bergeron thin liquid film setup was constructed and further employed in the investigation of foam and emulsions films. The films are formed in a porous glass plate immersed in the corresponding oil phase. The disjoining pressure is directly measured by means of a pressure transducer, and the thickness is determined via light interferometry. The disjoining pressure vs thickness isotherms show different features in respect to the stabilizing protein. When the films are stabilized by bovine serum albumin (BSA) and beta -lactoglobulin (BLG), a steric-like interaction comes into play being differently pronounced in the two cases. In contrast, the films stabilized with beta -casein exhibit classical Derjaguin-Landau-Verwey-Overbeek (DLVO) behavior. The disjoining pressure was converted to force adopting the Derjaguin approximation, and the result is compared with force-distance laws obtained employing magnetic chaining technique (MCT); there is an excellent agreement. Similar comparison with data obtained in a surface force apparatus (SFA) experiment reveals substantial discrepancies due to the different physical state of the proteins adsorbed at a liquid-liquid and a solid interface. The experiment reported here demonstrates one important possibility for realistic modeling of the interaction between emulsion droplets.

"Self-contained Microelectrochemical Immunoassay For Small Volumes Using Mouse IgG As A Model System"
Anal. Chem. 2002 Volume 74, Issue 14 Pages 3321-3329
Zoraida P. Aguilar, Walter R. Vandaveer, IV, and Ingrid Fritsch

Abstract: A self-contained, microelectrochemical immunoassay on the smallest volumes reported to date (1 µL for the antigen, 1 µL for the secondary antibody-enzyme conjugate, and 200 nL for the electrochemically detected species) has been developed using mouse IgG as a model system in a sandwich-type enzyme-linked immunosorbent assay, which takes less than 30 min to both complete the assembly of immunoassay components onto the antibody-modified surface and detect enzymatically generated species (excluding time for electrochemical cleaning of electrodes). These studies demonstrate the advantage of the close proximity of electrodes to modified surfaces and their application in the analysis of small volumes. Using a 50 mum diameter x 8 mum deep cavity with individually addressable electrodes on a microfabricated chip, the primary antibody was selectively and covalently attached at a gold, recessed microdisk (RMD) at the bottom of the microcavity to the free end of SAMs of either 11-mercaptoundecanoic acid or 11-mercapto-1-undecanol using 1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide hydrochloride. Nonspecific adsorption to the surrounding material, polyimide, of the microcavity device was eliminated. Electrochemical desorption was used to confine the immunoassay activity at the RMD. Enzymatic conversion of the substrate p-aminophenyl phosphate to p-aminophenol is detectable in less than 30 s using cyclic voltammetry at a gold, tubular nanoband electrode, which is on the wall of the microcavity and immediately adjacent to the modified RMD. A third electrode, also within the region of the microcavity, served as the pseudoreference/auxiliary electrode. Calibration curves obtained for 1 µL solutions of 5-100 ng/mL of IgG and for 200 nL-solutions of 5 muM to 4 mM of PAP(R) gave detection limits of 4.4 nM (6.4 ng/mL) or 880 fmol (129 pg) for PAPR and 56 fM (9 pg/mL) or 56 zmol (9 fg) for IgG. It is expected that the device may be suitable for analysis with volumes down to tens of picoliters.

"Novel Sorbents For Mercury Removal From Flue Gas"
Ind. Eng. Chem. Res. 2000 Volume 39, Issue 4 Pages 1020-1029
Evan J. Granite, Henry W. Pennline, and Richard A. Hargis

Abstract: A laboratory-scale packed-bed reactor system is used to screen sorbents for their capability to remove elemental mercury from various carrier gases. When the carrier gas is argon, an online atomic fluorescence spectrophotometer (AFS), used in a continuous mode, monitors the elemental mercury concentration in the inlet and outlet streams of the packed-bed reactor. The mercury concentration in the reactor inlet gas and the reactor temperature are held constant during a test. For more complex carrier gases, the capacity is determined off-line by analyzing the spent sorbent with either a cold vapor atomic absorption spectrophotometer (CVAAS) or an inductively coupled argon plasma atomic emission spectrophotometer (ICP-AES). The capacities and breakthrough times of several commercially available activated carbons as well as novel sorbents were determined as a function of various parameters. The mechanisms of mercury removal by the sorbents are suggested by combining the results of the packed-bed testing with various analytical results.

"Dual Analyte Flow Injection Fluorescence Immunoassays Using Thiophilic Gel Reactors And Synchronous Scanning Detection"
Analyst 2000 Volume 125, Issue 10 Pages 1707-1708
Jiu C. Guo, James N. Miller, Mark Evans and Derek A. Palmer

Abstract: Heterogeneous fluorescence immunoassays have been automated using flow injection manifolds incorporating thiophilic gel solid phase reactors to separate antibody-bound and unbound analyte molecules. Antibody elution is achieved by changes in ionic strength, thus allowing the use of pH sensitive fluorescent labels. This facilitates the development of dual analyte systems, in which two competitive immunoassays with separate labels are monitored in parallel. Detection of the fluorophores by high speed synchronous fluorescence scanning while the flow is briefly stopped utilises either one synchronous interval which detects both fluorophores, or two separate scans at different wavelength intervals, one for each fluorophore. Simultaneous analyzes of serum albumin and transferrin exemplify these novel approaches. Spectroscopic interferences are very small, analyte recoveries are close to 100%, with a relative standard deviation of 5-6% and a sampling rate of 20 h-1.

"Electrochemical Oxidation Of Hydrogen Peroxide At Platinum Electrodes. Part IV: Phosphate Buffer Dependence"
Electrochim. Acta 1999 Volume 44, Issue 25 Pages 4573-4582
Simon B. Hall, Emad A. Khudaish and Alan L. Hart

Abstract: The electrochemical oxidation of H2O2 at platinum rotating disc electrodes and microelectrodes was studied as a function of phosphate buffer concentration in the range 0-100 mM and pH from pH 4 to pH 10. The results were interpreted in terms of development of a surface binding site for H2O2 from a precursor site through interaction with H2PO4-from the electrolyte. In the absence of phosphate an alternative binding site mechanism was evident. The precursor site was shown to be inhibited by protons at low pH producing an inactive site.

"Development Of An Automated Sequential Injection On-line Solvent Extraction-back Extraction Procedure As Demonstrated For The Determination Of Cadmium With Detection By Electrothermal Atomic Absorption Spectrometry"
Anal. Chim. Acta 2002 Volume 456, Issue 2 Pages 283-292
Jianhua Wang and Elo Harald Hansen

Abstract: An automated sequential injection (SI) on-line solvent extraction-back extraction separation/pre-concentration procedure is described. Demonstrated for the assay of cadmium by electrothermal atomic absorption spectrometry (ETAAS), the analyte is initially complexed with ammonium pyrrolidinedithiocarbamate (APDC) in citrate buffer and the chelate is extracted into isobutyl methyl ketone (IBMK), which is separated from the aqueous phase by means of a newly designed dual-conical gravitational phase separator. A metered amount of the organic eluate is aspirated and stored in the PTFE holding coil (HC) of the SI-system. Afterwards, it is dispensed and mixed with an aqueous back extractant of dilute nitric acid containing Hg(II) ions as stripping agent, thereby facilitating a rapid metal-exchange reaction with the APDC ligand and transfer of the Cd into the aqueous phase. The aqueous phase is separated in a second dual-conical gravitational phase separator, and 30 µL of it is entrapped and metered in a sample loop (SL) and subsequently introduced via air segmentation into the graphite tube for analyte quantification. The ETAAS determination is performed in parallel with the separation/pre-concentration process of the ensuing sample. An enrichment factor of 21.4, a detection limit of 2.7 ng L-1, along with a sampling frequency of 13 h-1 were obtained at a sample flow rate of 6.0 mL min-1. The precision (RSD) at the 0.4 µg L-1 level was 1.8% as compared to 3.2% when quantifying the organic extractant directly. The applicability of the procedure is demonstrated for the determination of trace levels of cadmium in three certified reference materials.

"Speciation And Oxidation Kinetics Of Arsenic In The Thermal Springs Of Wiesbaden Spa, Germany"
Fresenius J. Anal. Chem. 2001 Volume 371, Issue 7 Pages 927-933
Susanne P. Schwenzer, Caterina E. Tommaseo, Michael Kersten, Thomas Kirnbauer

Abstract: Since 1886 arsenic has been known to be present as a trace component in the Wiesbaden thermal waters at concentrations of over 100 µg L-1. In this study for the first time molecular level speciation of arsenic was measured both in the water (by HG-AAS) and in well-stone scale deposits (by XANES). Most of the arsenic in the anoxic NaCl-type waters is in the reduced arsenite form. Hydrous ferric oxide (HFO) precipitates in the scale deposits scavenge only the minor dissolved arsenate portion which is, however, accumulated up to 3% w/w. Isothermal precipitation experiments at in-situ temperatures showed a difference between the progress of both arsenic and iron oxidation and precipitation. This can be explained in terms of adsorption of the aqueous arsenite and heterogeneous oxidation on the HFO surface, but subsequently rapid release of the arsenate thereby formed back into the aqueous phase at enhanced temperature and increased pH. Such relatively rapid pseudo-homogeneous arsenite oxidation is too slow to efficiently retard the As(III) load already on the wellhead, but fast enough to prevent arsenic seepage into ground water aquifers.

"Flow Analysis-based Surface-enhanced Raman Spectroscopy Employing Exchangeable Microbeads As SERS-active Surfaces"
Appl. Spectrosc. 2000 Volume 54, Issue 7 Pages 1012-1018
Bernhard Lendl, Horst Ehmoser, Johannes Frank, and Rupert Schindler

Abstract: This paper reports on a new fully automated approach for highly sensitive and robust surface-enhanced Raman spectroscopic (SERS) detection using flow systems. An aqueous solution of silver nitrate was reduced by the addition of sodium borohydride and the thus formed silver sols adsorbed on Sephadex anion exchanger microbeads (dry bead size: 50-120 µm) present in the reaction mixture. In this way microbeads carrying a SERS-active layer were generated that could be easily pumped in the how system without facing problems due to Ag-sol adsorption on the Teflon(R) tubing. After online generation of the SERS-active microbeads, the analyte (test analyte: nicotinic acid) was added, and the homogeneous SERS-microbead-analyte suspension pumped into a specially designed dow cell where the beads were retained and the SERS spectra measured with a Fourier transform (FT)-Raman instrument with a laser wavelength of 1064 nm. Afterwards the SERS microbeads were discarded by flow reversal and new, freshly prepared SERS microbeads together with the analyte could be introduced automatically into the flow system. The developed method is characterized by complete computer control of all operation steps, high sensitivity of the SERS measurement, high precision, and long-term stability. The concentration dependence of the SERS signals was investigated over a range from 5.10^-6 M to 0.1 M nicotinic acid. The signal intensities increased until 1 mM, after which no further rise in the SERS intensities was found. Typical precision achieved was 8% throughout the whole calibration range.

"Quaternized Wood As Sorbent For Hexavalent Chromium"
Appl. Biochem. Biotechnol. 2001 Volume 90, Issue 1 Pages 75-87
Low, Kun-She; Lee, Chnoong-Kheng; Lee, Chun-Yuan

Abstract: The potential of quaternized wood (QW) chips in removing hexavalent chromium from synthetic solution and chrome waste under both batch and continuous-flow conditions was investigated. Sorption was found to be dependent on pH, metal concentration, and temperature. QW chips provide higher sorption capacity and wider pH range compared with untreated wood chips. The equilibrium data could be fitted into the Langmuir isotherm model, and maximum sorption capacities were calculated to be 27.03 and 25.77 mg/g in synthetic chromate solution and chrome waste, respectively. The presence of sulfate in high concentration appeared to suppress the uptake of chromium by QW chips. Column studies showed that bed depth influenced the breakthrough time greatly whereas flow rate of influent had little effect on its sorption on the column.

"Construction And Evaluation Of A Flow-through Cell Adapted To A Commercial Static Mercury Drop Electrode (SMDE) To Study The Adsorption Of Cd(II) And Pb(II) On Vermiculite"
Talanta 2002 Volume 58, Issue 3 Pages 433-443
Gilberto Abate, Jaim Lichtig and Jorge C. Masini

Abstract: This paper describes the construction and application of a robust flow-through cell for use with the capillary of a commercial static mercury drop electrode. Linearity of peak current was observed up to 0.50 µmol L-1 for Cd(II) or Pb(II) in anodic stripping voltammetry experiments performed under continuous flow during the deposition step, using 120 s of deposition time and flow rate of 4.0 mL min-1. Under these conditions the limits of detection for Cd(II) and Pb(II) were 13 and 17 nmol l-1, respectively. An analytical throughput of 20 analyzes per h was possible using 10 s for cleaning the cell between two samples and including the time needed for the potential scan, which was performed with the flow stopped, using the differential pulse mode for current sampling. The linear dynamic range can be extended up to 5 µmol L-1 for both cations if the deposition time is decreased to 30 s, a condition in which the sampling throughput is 35 analyzes per h. The proposed manifold was used to study the adsorption rates of Cd(II) and Pb(II) onto vermiculite at different pHs, allowing one to perform high sensitivity measurements at high sampling frequency, using low cost instrumentation.

"Binding Assays In Heterogeneous Media Using A Flow Injection System With An Expanded Micro-bed Adsorption Column"
Bioseparation 1999 Volume 8, Issue 1-5 Pages 237-45
Bo Mattiasson, M. P. Nandakumar

Abstract: Competitive binding assays have been performed in flow injection systems. To further increase the versatility of the system, and to enable it to deal with samples containing particulate matter, the adsorption step was designed as an expanded bed column. Immunochemical quantification of human serum albumin was chosen as a model system to use for the development of the technology. A competitive ELISA was set up using peroxidase labelled HSA as competing ligand. The introduction of the expanded bed immunosorption column made the system tolerant to samples containing suspended particulate matter. The analytical outcome is very similar to that from the packed bed system even though more time is required for each assay cycle. The capability of the system was tested by addition of increasing amounts of yeast cells. The results clearly indicate that the system is suitable e.g. for process monitoring of fermentations.

"Soil-modified Carbon Paste Electrode: A Useful Tool In Environmental Assessment Of Heavy Metal Ion Binding Interactions"
Fresenius J. Anal. Chem. 2000 Volume 367, Issue 8 Pages 701-706
Irena Grabec Svegl, Bozidar Ogorevc

Abstract: Carbon paste electrodes (CPEs) modified with different soils in their native form were prepared to create a soil-like solid phase suitable fur application in studies of heavy metal ion uptake and binding interactions. The preparation of CPEs modified with five different soils was examined and their heavy metal ion uptake behavior investigated using a model Cu(II) aqueous solution. Metal ions were accumulated under open circuit conditions and were determined after a medium exchange using differential pulse anodic stripping voltammetry, applying pre-electrolysis at -0.7 V. The soil-modified CPE accumulation behavior, including the linearity of the current response versus Cu(II) concentration, the influence of the pH on the solution, and the uptake kinetics, was thoroughly investigated. The correlation between the soil-modified CPE uptake capability and the standard soil parameters, such as ion exchange capacity, soil pH, organic matter and clay content, were evaluated for all five examined soils. The influence of selected endogenous cations (K(I), Ca(II), Fe(III)) on the transfer of Cu(II) ions from a solution to the simulated soil solid phase was examined and is discussed. Preliminary examinations of the soil-modified CPE uptake behavior with some exogenous heavy metal ions of strong environmental interest (Pb(II), Ng(II), Cd(II) and Ag(I)) are also presented. This work demonstrates some attractive possibilities fur the application of a soil-modified CPE in studying soil-heavy metal ion binding interactions, with a further potential use as a new environmental sensor appropriate fur fast on-site testing of polluted soils.

"Determination Of Trace Bismuth By Solid Phase Extraction And Anodic Stripping Voltammetry In Non-aqueous Media"
Anal. Chim. Acta 2001 Volume 437, Issue 2 Pages 217-224
M. H. Pournaghi-Azar, Dj. Djozan and H. Abdolmohammad zadeh

Abstract: The voltammetric characteristics of BL(III) oxinate at the mercury electrode in chloroform are investigated. Anodic stripping voltammetry (ASV) for the determination of trace bismuth was developed in chloroform, using the differential pulse technique to strip the amalgamated bismuth from hanging mercury drop electrode (HMDE). The experimental variables such as scan rate of electrode potential, deposition potential, deposition time and stirring speed were optimized. The linear range of calibration graph and the detection Limit were 5 x 10^-8 to 5 x 10^-6,d 3.5 x 10^-9 M for Bi(III), respectively. Preceded by a pre-concentration stage by solid phase extraction using octylsilane (RP-8) cartridge and subsequent elution by chloroform, the detection limit of the method is improved in 4.5 x 10^-10 M. The suitability of the proposed method for determination of trace bismuth in real sample was established by the analysis of a metallic aluminum sample.

"Adsorption Of Cationic Poly (diallyl-dimethyl-ammoniumchloride), Poly (diallyl-dimethyl-ammoniumchloride-co-N-methyl-N-vinylactamide) And Poly (N-methyl-N-vinyl-acetamide) On Polystyrene Latex"
Colloid Surf. A 1999 Volume 149, Issue 1-3 Pages 323-328
Roland Rehmet and Erwin Killmann

Abstract: Isotherms of the cationic polyelectrolyte poly (diallyl-dimethyl-ammoniumchloride), poly (diallyl-dimethyl-ammoniumchloride-co-N-methyl-N-vinylacetamid) and neutral poly(N-methyl-N-vinyl-acetamide) on polystyrene latex were determined by measuring the concentration of the polymer in the supernatant solution with polyelectrolyte titration. All isotherms are of the high affinity type. The adsorbed amount rises with the concentration of salt and with the decrease of polyelectrolyte charge density. At high concentrations of salt the adsorbed amount increases with the molar mass. The procedure for the polyelectrolyte titration of polyelectrolyte solutions with high salt concentrations was performed after dialysis against hydrochloric acid.

"Adsorption-desorption Studies Of Ketones At A Hanging Mercury Drop Electrode By A Flow Injection Method"
Anal. Sci. 1999 Volume 15, Issue 1 Pages 73-78
Hiromiti Sawamoto

Abstract: The adsorption-desorption phenomena of ketones were studied by measuring differential capacity-time curves in a flowing solution. The ketones investigated were acetone, 2-butanone, 3-pentanone and 4-heptanone. The differential capacity-time curves for these ketones showed different shapes with and without peaks. The curves were used to study the adsorption reversibility of the ketones at a mercury electrode. The adsorption of acetone was irreversible and that of 3-pentanone and 4-heptanone was reversible. The adsorption of 2-butanone was rather complicated. It seems that two types of adsorption exist for 2-butanone.

"Speciation Of As(III) And As(V) In Aqueous Solutions Using Bakers Yeast And Hydride Generation Inductively Coupled Plasma Atomic Emission Spectrometric Determination"
J. Anal. At. Spectrom. 2000 Volume 15, Issue 11 Pages 1493-1497
Patricia Smichowski, Julieta Marrero, Ariel Ledesma, Griselda Polla and Daniel A. Batistoni

Abstract: The use of Saccharomyces cerevisiae was evaluated as substrate for the biosorption of As(III) in the presence of As(V), for the determination of these species in aqueous solutions. Experiments were performed in batch to find a suitable and simple method to obtain information on arsenic uptake. The effect of chemical and physical variables affecting the biosorption of As were tested in order to select the optimal analytical conditions for the selective As retention by Saccharomyces cerevisiae. The parameters studied were: reaction media and pH, amount of biomass, analyte concentration and contact time. The influence of some concomitant ions up to a concentration of 50 mg L-1 was also tested. Quantitative determinations of As species in yeast and supernatant solution were carried out by means of inductively coupled plasma atomic emission spectrometry with hydride generation. During all the steps of the optimization process, As(V) remained in solution while As(III) was accumulated by the yeast cells. A pre-concentration factor of 7 was achieved for As(III) when 35 mL of water were processed. The detection limits for As(III) and As(V) were 0.1 and 0.5 ng mL-1, respectively. The speciation of inorganic As in different kinds of natural waters was performed following the proposed method. Spiked water samples were also analyzed and the recoveries in each phase were in all cases between 92 and 106%.

"Preparation Of Stable, Reproducible Silver Colloids For Use As Surface-enhanced Resonance Raman Scattering Substrates"
Appl. Spectrosc. 2002 Volume 56, Issue 5 Pages 551-559
Ruth Keir, Daran Sadler, and W. E. Smith

Abstract: A flow system for the production of stable, reproducible batches of silver colloid for use as substrates for surface-enhanced resonance Raman spectroscopy (SERRS) is described. The colloids were prepared by borohydride reduction of silver nitrate and subsequent stabilization was achieved by adding trisodium citrate. The batches of colloid produced were analyzed using UV-visible spectroscope and their suitability for use as SERRS substrates was assessed using 3,5-dimethoxy-4-(5-azobenzotriazole)phenylamine as the analyte. SERRS analysis was carried out using a flowcell. Using the method described, batches of silver colloid were prepared that were stable for at least five months and when used as SERRS substrates resulted in a relative standard deviation in SERRS intensity of 3,5dimethoxy-4-(5-azobenzotriazole)phenylamine of 6.6% between colloid batches. The robustness of the system for production of stable, reproducible colloids was assessed using experimental design. The final method proposed enables reproducible, time-stable colloid to be made in a simple manner, thus eliminating one of the major problems associated with the use of SERRS detection in analytical procedures.

"Flame Atomic Absorption Spectrometric Determination Of Chromium(VI) By On-line Preconcentration System Using A PTFE Packed Column"
Talanta 2002 Volume 57, Issue 1 Pages 15-22
Aristidis N. Anthemidis, George A. Zachariadis, John-S. Kougoulis and John A. Stratis

Abstract: A new, sensitive and robust time-based flow injection (FI) method for on-line pre-concentration and determination of ultra trace amounts of chromium(VI) by flame atomic absorption spectrometry (FAAS) has been elaborated. The sample is initially mixed on-line with ammonium pyrrolidine dithiocarbamate (APDC) and the Cr(VI)-PDC chelate is absorbed quantitatively on a mini-column packed with polytetrafluoroethylene (PTFE) turnings at a pH range 0.8-1.4. The complex is subsequently eluted with isobutyl methyl ketone (IBMK) and introduced directly into the nebulizer-burner system. The optimized system offered improved performance characteristics, with unlimited lifetime of the proposed column. The enhancement factor was 80, for a 3-min pre-concentration time and the sample frequency was 18 h-1. The calibration curve was linear over the concentration range 1-40 µg L-1 with a detection limit of c(L) = 0.8 µg L-1 and a relative standard deviation of s(r) = 3.2%, at the 20 µg L-1 level. The proposed method was evaluated by analyzing samples of certified and spiked water, and it was applied to the analysis of natural water samples and sediments. (C) 2002 Elsevier Science B.V. All rights reserved.

"Novel Calibration Of A Dynamic Surface Tension Detector: Flow Injection Analysis Of Kinetically-hindered Surface Active Analytes"
Talanta 1999 Volume 50, Issue 5 Pages 1045-1056
Keith E. Miller, Kristen J. Skogerboe and Robert E. Synovec

Abstract: First, a novel technique for calibration of a dynamic surface tension detector (DSTD) is described. The DSTD measures the differential pressure as a function of time across the liquid-air interface of growing drops that repeatedly form and detach at the end of a capillary tip. The calibration technique utilizes the ratio of pressure signals acquired from the drop growth of two separate solutions, i.e. a standard solution and a corresponding mobile phase, such as water, both of which have a known surface tension. Once calibrated, the dynamic surface tension of an analyte is obtained from the ratio of the pressure signals from the analyte solution to that of the mobile phase solution. Thus, this calibration technique eliminates the need to optically image the radius of the expanding drop of liquid. Accurate dynamic surface tension determinations were achieved for aqueous sodium dodecyl sulfate (SDS) solutions over a concentration range of 0.5-5.4 mM. The measured surface tensions for these SDS solutions range from 70.3 to 46.8 dyne/cm and were in excellent agreement with the literature. A precision of 0.2 dyne/cm (1 S.D.) was routinely obtained. Second, the DSTD with this calibration technique was combined with flow injection analysis (FIA) for the study of model protein solutions and polymer solutions. The kinetic surface tension behavior of aqueous bovine serum albumin (BSA) solutions as a function of concentration and flow rate is presented. Evaluation of the dynamic surface tension data illustrates that a protein such as BSA initially exhibits kinetically-hindered surface tension lowering, i.e. a time dependence, as BSA interacts with the liquid-air interface of an expanding drop. FIA/DSTD is then shown to be an effective tool for the rapid study of kinetically-hindered surfactant mixtures. It was found that mixtures of SDS and the polymeric surfactant Brij(R)-35 (lauryl polyoxyethylene ether with an average molecular weight of 1200 g/mol) result in essentially an additive lowering of the surface tension. Mixtures of polyethylene glycol (PEG), with an average molecular weight of 1470 g/mol, and Brij(R)-35, however, result in a competitive (non-additive) surface tension with the Brij(R)-35 dominating the response.

"Studies Of An Alkaline Activated Glassy Carbon Electrode On The Determination Of Purines And DNA"
J. Chin. Chem. Soc. 1999 Volume 46, Issue 2 Pages 233-238
Tang, Tzyh-Chyang ; Huang, Hsuan-Jung

Abstract: Performance of glassy carbon electrode on the determination of purines and DNA was found to be improved dramatically by activating time GCE with a simple but effective electrochemical pretreatment. Characteristics such as lowering of oxidation potential, enhancement of peak current and elimination of fouling effect were found for the activated GCE. By flow injection analysis, good reproducibility with relative standard deviations of 0.59 and 2.01% (n = 11) land rather low detection limits of 0.6±0.1 and 3.0±0.4 nM can be obtained for the analysis of guanine and adenine. Solutions of denatured calf thymus DNA were analyzed by differential pulse voltammetry with the activated GCE. Good agreement between the obtained results and the known values confirms the feasibility of the activated GCE for DNA analysis.

"Modified Carbon Paste Electrodes For Flow Injection Amperometric Determination Of Isocitrate Dehydrogenase Activity In Serum"
Anal. Biochem. 2002 Volume 308, Issue 2 Pages 195-203
Pablo Rodríguez-Granda, M. Jesús Lobo-Castañón, Arturo J. Miranda-Ordieres and Paulino Tuñón-Blanco

Abstract: A carbon paste electrode modified with the adsorbed products of the electrochemical oxidation of adenosine triphosphate is described. The electrode was applied to the amperometric electrocatalytic detection of the reduced form of both nicotinamide adenine dinucleotide and nicotinamide adenine dinucleotide phosphate. The catalytic oxidation current shows a linear dependence on the concentration of the reduced form of nicotinamide adenine dinucleotide up to 1 x 10^-4M, with a detection limit of 5 x 10^-9M. Modified carbon paste electrodes were coated with an electrogenerated film of nonconducting poly(o-phenylenediamine) to obtain a stable amperometric response for at least 150 h. In addition to static measurements, determination of both reduced cofactors was carried out in a flow injection analysis system with a thin-layer amperometric detection cell. The electrocatalytic monitoring of reduced nicotinamide adenine dinucleotide phosphate was applied to flow injection measurement of isocitrate dehydrogenase activity in serum. The results were in good agreement with those for the standard spectrophotometric test kit. The proposed method consumed less time and reagents and provided better precision than the standard method.

"Seasonal Variability In The Kinetics Of Cu, Pb, Cd And Hg Accumulation By Macroalgae"
Mar. Chem. 2001 Volume 74, Issue 1 Pages 65-85
M. Teresa S. D. Vasconcelos and M. Fernanda C. Leal

Abstract: Here it is demonstrated that both Porphyra spp. and Enteromorpha spp. of macro-algae display similar and very marked seasonal variations in their concentration factor (CF) of Cu, Pb, Cd and Hg in field conditions. The CF variations are specific for each metal and reproducible over several years. The way variations in the biological activity affect the equilibrium and kinetics of the interaction between trace metals and live algae was studied in vitro. Natural seawater was used as the culture medium. Voltammetry was used for the determination of natural organic ligands and trace metals except Hg, which was determined by mercury cold vapor after on-line pre-concentration. Titrations with the relevant metal demonstrated that the maximum binding capacity of the algae was not significantly dependent on the season for Pb (ca. 100 µmol g(dry algae)-1), Cd (ca. 50 µmol g-1) and Hg (80-100 µmol g-1). Marked seasonal variations were observed for Cu (ca. 40 µmol g-1 in January; 70 µmol g-1 in May; and 100 µmol g-1 in August). The conditional stability constants of metal-algae complexation sites were seasonally independent and similar for both algae: log K-MS = 8.5±0.3 (Cu), 5.6±0.2 (Pb), 5.3±0.2 (Cd) and 18.0±0.3 (Hg). Exudates with a strong Cu complexing capacity (log K-CuL = 12.47±0.06) were determined in cultures with added Cu, Pb or Cd concentrations, and identified by cathodic stripping voltammetry (CSV) as cysteine or glutathione. All the tested metals promoted the liberation of exudates, both cysteine- and glutathione-like ligands were exuded in the presence of Cu, only cysteine-like ligands in the presence of Pb, and only glutathione-like ligands in the presence of Cd, the rise depending of the season of the year, particularly for Cu. Highest levels were produced in the presence of added Pb. When exposed to either 1- or 100-muM total dissolved metal concentrations, the metal uptake, and its rate, varied with the season and the algae. (C) 2001 Elsevier Science B.V. All rights reserved.

"Separation And Preconcentration Of Fluoride At The Ng Ml(-1) Level With A Polymer Complex Of Zirconium(IV) Followed By Potentiometric Determination In A Flow System"
Anal. Chim. Acta 1999 Volume 388, Issue 1-2 Pages 201-208
Akio Yuchi, Kaoru Matsunaga, Tomoko Niwa, Hirohito Terao and Hiroko Wada

Abstract: A complex of Zr(IV) with a hydrophilic resin having an iminodiacetic acid group rapidly and selectively adsorbed fluoride from acidic media, which was reversibly expelled on increase in pH. A Bow system consisting of a mini-column packed with this polymer complex for separation and pre-concentration of fluoride and an ion-selective electrode for detection gave the same peak height for the same amount of fluoride, irrespective of the sample concentration and volume, and thus could be calibrated based on the chemical amount; the detection limit defined by S/N=3 was 0.1 nmol. Use of the Bow system decreased the lower limit for quantitative adsorption of fluoride down to 5 x 10^-8 M (compared with 1 x 10^-4 M by batch adsorption), and drastically increased the tolerance limits of interfering cations and anions; even the presence of a fourfold molar ratio of Al3+ was tolerated with cyclohexane diamine tetraacetic acid as masking reagent. This system was applied to the determination of fluoride in drinking water and concentrated brine. The adsorption and desorption mechanism is discussed in detail.

"Separation And Preconcentration Of Fluoride At The Ng Ml(-1) Level With A Polymer Complex Of Zirconium(IV) Followed By Potentiometric Determination In A Flow System"
Anal. Chim. Acta 1999 Volume 388, Issue 1-2 Pages 201-208
Akio Yuchi, Kaoru Matsunaga, Tomoko Niwa, Hirohito Terao and Hiroko Wada

Abstract: A complex of Zr(IV) with a hydrophilic resin having an iminodiacetic acid group rapidly and selectively adsorbed fluoride from acidic media, which was reversibly expelled on increase in pH. A Bow system consisting of a mini-column packed with this polymer complex for separation and pre-concentration of fluoride and an ion-selective electrode for detection gave the same peak height for the same amount of fluoride, irrespective of the sample concentration and volume, and thus could be calibrated based on the chemical amount; the detection limit defined by S/N=3 was 0.1 nmol. Use of the Bow system decreased the lower limit for quantitative adsorption of fluoride down to 5 x 10^-8 M (compared with 1 x 10^-4 M by batch adsorption), and drastically increased the tolerance limits of interfering cations and anions; even the presence of a fourfold molar ratio of Al3+ was tolerated with cyclohexane diamine tetraacetic acid as masking reagent. This system was applied to the determination of fluoride in drinking water and concentrated brine. The adsorption and desorption mechanism is discussed in detail.

"Studies Of Potential-dependent Metallothionein Adsorptions Using A Low-volume Electrochemical Quartz Crystal Microbalance Flow Cell"
J. Electroanal. Chem. 2001 Volume 513, Issue 1 Pages 16-24
Alejandro L. Briseno, Fayi Song, Alfred J. Baca and Feimeng Zhou

Abstract: Adsorptions of metallothioneins (MTs) onto thin mercury films (TMFs) at potentials more negative or positive than the point of zero charge (pzc) of mercury were quantified for the first time, using a novel electrochemical quartz crystal microbalance (EQCM) flow cell in conjunction with a simple flow injection system (FI-EQCM). The EQCM flow cell has a low internal volume (ca. 50 µL) designed for the investigation of biomolecular attachment to surfaces. Such a cell facilitates in-situ gravimetric measurements of MT adsorption processes at different potentials. The amount of the MT adsorption at - 0.9 V, a potential more negative than the pzc of the TMF, was found to be greater than that attached via simple chemisorption (in an open-circuit configuration). The quantity of metals released by the MT adsorbates, measured by electrochemical inductively coupled plasma-atomic emission spectrometry (EC/ICP-AES), was found to constitute similar to 3.8% of the total mass measured by FI-EQCM. The average number of cysteines per MT molecule involved in the Hg-cysteine thiolate formation was found to be 4.2±1.8. Thus, it appears that about 1-2 metal ions (Cd2+) per MT molecule have been released off the TMF electrode since the stoichiometric, ratio between the Cd2+ and the cysteines in a MT molecule is known to be 1/3. The quantitative measurements by the two hybrid electrochemical methods (FI-EQCM and EC/ICP-AES) help elucidate the electrode reactions of MT adsorbates at TMF surfaces and the MT metal transfer processes. (C) 2001 Elsevier Science BN. All rights reserved.

"Sequential Extraction And Analysis Of Phosphorus In Marine Sediments: Streamlining Of The SEDEX Procedure"
Limnol. Oceanogr. 2000 Volume 45, Issue 2 Pages 509-515
L. D. Anderson, M. L. Delaney

Abstract: We streamlined the five-step SEDEX (sedimentary extraction) procedure for characterizing sedimentary phosphorus to a four-step procedure. We combined extraction of adsorbed and oxide-associated pools into a single step, retaining steps for authigenic, detrital, and organic P. In addition, we used automated spectrophotometric flow injection analysis (FIA) to determine P concentrations, rather than traditional spectrophotometric tech-niques. We decreased our total extraction and analytical time from 12 d for 24 replicate samples to 5 d without sacrificing our geo-chemical objectives, detection limits, or analytical reproducibility.

"Development Of A Theoretical Model For Chromatographic-based Competitive Binding Immunoassays With Simultaneous Injection Of Sample And Label"
Anal. Chem. 1999 Volume 71, Issue 15 Pages 2965-2975
David S. Hage, David H. Thomas, A. Roy Chowdhuri, and William Clarke

Abstract: This study examined the theory and behavior of an HPLC-based chromatography competitive binding immunoassay with the simultaneous injection of sample and a labeled analyte analog. Equations based on nonlinear chromatography theory were derived to describe the calibration curve for this assay in a system with adsorption-limited kinetics and homogeneous binding sites. These equations related the assay response (B/Bo) to the columns binding capacity, the moles of injected analyte or labeled analog, and the flow rate/adsorption kinetics of the system. There was good agreement between the predicted theoretical response and experimental data obtained for the binding of human serum albumin (HSA) to an immobilized anti-HSA antibody column. This theory was also successful in describing the changes that occurred in the calibration curve when the flow rate or amt. of labeled analog applied to the column was varied. A comparison was made between the results of this study and previous theoretical work that examined the behavior of a related, sequential injection competitive binding method. On the basis of the results reported in this work, several general guidelines were developed for the design and optimization of simultaneous injection methods for use in such areas as clinical testing, pharmaceutical anal., and environmental monitoring.

"Interfacial Properties Of Biotin Conjugate-avidin Complexes Studied By Acoustic Wave Sensor"
Langmuir 1999 Volume 15, Issue 2 Pages 564-572
Shakour Ghafouri and Michael Thompson

Abstract: The adsorption of avidin, neutravidin, and biotin-labeled dextran 10,000, dextran 70,000, bovine albumin, and insulin to the gold electrodes of thickness-shear-mode acoustic wave devices was studied in a flow injection analysis configuration. Electrodes with different surface rugosity and free energy were also examined Changes in series resonance frequency for the various molecules as a result of electrode adsorption cannot be explained in terms of the conventional mass-response effect. Perturbation of the properties of the protein and polysaccharide layers, such as their viscosity, and acoustic coupling phenomena offer a more reasonable basis to evaluate the results. In an analogous fashion, the acoustic wave sensor signals obtained for the formation of the various avidin-and neutravidin-biotin conjugate samples do not correspond to the additional mass deposited on the device surface. The responses for the binding of biotinylated insulin to avidin and to the nonglycosylated form of the parent mol. were completely different. This result is ascribed to a difference of surface free energy associated with the two protein-based interfaces. The acoustic wave sensor was also employed to investigate the formation of avidin-biotin conjugate multilayer structures on the surface of the device. Multilayer buildup is detectable for several pairs of avidin-biotin interactions, but the corresponding shifts in series resonance frequency gradually diminish in magnitude. Finally, the introduction of biotin itself appears to result in structural changes in the multilayer deposit, causing alterations in viscoelastic properties.

"Adsorption-desorption Phenomena Of Sodium Dodecyl Sulfate And Sodium Dodecylbenzenesulfonate At A Hanging Mercury Drop Electrode"
Nippon Kagaku Kaishi 1998 Volume 1998, Issue 7 Pages 511-513
Hiromiti SAWAMOTO

Abstract: Adsorption-desorption phenomena of sodium dodecyl sulfate and sodium dodecylbenzenesulfonate at a mercury electrode were studied by flow injection method with measuring differential capacity-time curves. Adsorption of sodium dodecyl sulfate at -0.2 V is irreversible, while that at the potential more negative than -0.4 V is reversible. Adsorption of sodium dodecylbenzenesulfonate is irreversible at the potential morepositive then -0.8 V. It is reversible at the potential more negative than -1.0 V. From these results, adsorption models for the two surfactants were proposed.
Sodium dodecyl sulfate Sodium dodecylbenzenesulfonate Electrode