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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Jens E. T. Andersen

Abbrev:
Andersen, J.E.T.
Other Names:
Address:
Department of Chemistry, Technical University of Denmark, Building 207, DK-2800 Lyngby, Denmark
Phone:
+45-45-252348
Fax:
+45-45-883136

Citations 9

"Flow Injection Responses Of Diffusion Processes And Chemical Reactions"
Theor. Chem. Acc. 2000 Volume 103, Issue 5 Pages 409-416
Jens E.T. Andersen

Abstract: The technique of flow-injection analysis (FIA), now 25 years old, offers unique analytical methods that are fast, reliable and consume an absolute minimum of chemicals. These advantages together with its inherent feasibility for automation warrant the future application of FIA as an attractive tool of automated analytical chemistry. The need for an even lower consumption of chemicals and for computer analysis has motivated a study of the FIA peak itself, i.e., a theoretical model that provides detailed knowledge of the FIA profile was developed. It was shown that the flow in a FIA manifold may be characterized by a diffusion coefficient that depends on the flow rate, denoted as the kinematic diffusion coefficient. The description was applied to systems involving species of chromium, both in the case of simple diffusion and in the case of chemical reaction. It is suggested that the description may be used in the resolution of FIA profiles to obtain information about the content of interferences, in the study of chemical reaction kinetics and to measure absolute concentrations within the FIA-detector cell.
Diffusion Theory

"On The Possibility To Improve The Performance Of Flow Injection Analysis By Deconvolution Of Spectrophotometric Data"
Talanta 2001 Volume 54, Issue 1 Pages 131-138
Jens E. T. Andersen

Abstract: The concentration profile of chemical species pumped through a tubular system of 0.5-mm inner diameter is found to be trapezial shaped, as described theoretically by including the spatial resolution of the instrument, friction and diffusion. By applying the theory, which is based on the concept of segment flow. to experiments, it is shown that an injected segment of solute is diluted predominantly at the front and at the tail proportion of the segment in motion. A double-peaked structure in experiments of Row-injection analysis (FIA) was identified and by including all the data of the experimentally measured responses. it was possible to obtain an improvement of the sensitivity by a factor of 22 and obtain almost a factor of three times improvement on the standard deviation. (C) 2001 Elsevier Science B.V. All rights reserved.
Theory

"On-line Speciation Of Cr(III) And Cr(VI) By Flow Injection Analysis With Spectrophotometric Detection And Chemometrics"
Rev. Roum. Chim. 2003 Volume 48, Issue 4 Pages 271-278
DIACU Elena ; ANDERSEN Jens E. T.

Abstract: A flow injection system has been developed, for on-line speciation of Cr(III) and Cr(VI) by the Diphenylcarbazide (DPC) method with H 2O2 oxidation followed by spectrophotometric detection at the 550 nm wavelength. The data thus obtained were subjected to a chemometric analysis (PLS), which showed that it was possible to obtain reliable predictions of Cr(III) and Cr(VI) species. The method was validated on samples of stainless steel. In order to facilitate analysis of stainless-steel samples, it was essential to perform a step of evaporation to dryness followed by re-dissolution. The analysis showed that species of Cr(III) and Cr(VI) coexisted in the samples digested by this method. By spiking the samples with iron and nickel species, it was found that, although the total amount of chromium remained constant, the equilibrium of the two chromium species was displaced towards Cr(III). A detection limit of 10 ?g/L and a maximum sampling frequency of 120 injections per hour were obtained, excluding calculations and sample pre-treatments.

"Indications Of Segmental Flow In Straight Pipes By Flow Injection With Spectrophotometric Detection"
Phys. Scr. 2000 Volume 62, Issue 4 Pages 331-340
Jens T. Anderson

Abstract: A procedure of spectrophotometric analysis of fluid how in pipes is described and its performance is tested on three different dye compounds. The procedure follows measurement and mathematical de-convolution of the signal with an exponential function that is associated with molecular diffusion. Evidence is provided for the presence of segmental how and the three dye compounds, used as tracer molecules, indicate that the solute molecules gain velocity, predominantly in the streamwise direction, from the solvent how rate. The additional velocity, as gained from the solvent flow rate, depends on a kinetic-diffusion constant and the internal friction of the system. The model allows a calculation of the dow-injection signal and serves as a tool for the investigation of properties of fluid dynamics.
Dispersion

"Theoretical Considerations Of Flow Injection Analysis In The Absence Of Chemical Reactions"
J. Flow Injection Anal. 2000 Volume 17, Issue 1 Pages 59-64
J. E. T. Andersen

Abstract: NA

"Filterless Pre-concentration By Co-precipitation By Formation Of Crystalline Precipitate In The Analysis Of Barium By FIA-FAES"
J. Anal. At. Spectrom. 2003 Volume 18, Issue 1 Pages 49-53
Christoffer Plamboeck, Hans C. Westtoft, Sune A. Pedersen and Jens E. T. Andersen

Abstract: A novel method based on flow injection analysis (FIA) and flame atomic emission spectrometry (FAES) is presented. It was developed for direct determination of barium in drinking water, in natural water, in digested samples of bone and liver, in saline water and in a standard reference material (NIST SRM 1640). It was found that digestion of bone by an incineration procedure was required, in order to extract most of the barium. In the FIA manifold, barium was pre-concentrated by co-precipitation with lead chromate leading to a crystalline deposit that adhered well to the inner walls of a nylon knotted reactor (KR). The method documents a novel example of formation of a crystalline compound during the pre-concentration step. The method comprises filterless pre-concentration by co-precipitation that proceeds successfully in a FIA system. An enrichment factor (EF) of 24 was achieved under normal working conditions at a sampling frequency of 50 h-1. The detection limit (LOD, 3s) was determined as 0.8 µg L-1 and species of iron(II) and iron(III) constituted the main species of interference.

"Improved Performance Of The Potentiometric Biosensor For The Determination Of Creatinine"
Anal. Lett. 2007 Volume 40, Issue 1 Pages 39-52
Claus Dallerup Rasmussen; Jens E. T. Andersen; Birgit Zachau-Christiansen

Abstract: Contemporary methods of analyzing creatinine engage chemicals harmful to the environment and generate large volumes of waste disposals. By introducing a membrane-based potentiometric biosensor with immobilized creatinine deaminase, the measurements can be performed by miniaturized portable devices that are easy to handle and allow rapid analysis with minimum consumption of chemicals. Thus, the enzymatic creatinine biosensors were revisited and optimized with respect to repeatability, sensitivity, limit of detection (LOD), and response time. A detection limit of 0.3 ?M and a sensitivity of 58.78 ±0.03 mV (23.5°C) were obtained in tris buffer at pH=7.4 after introduction of shielding of all electronics and software filtering. Measurements performed by flow injection analysis (FIA) showed that the response time could be lowered to approximately 30 sec using sample volumes of 30 µL. Interferences were corrected for by application of the Nicolsky-Eisenman equation, thus allowing determination of creatinine in matrices resembling those of clinical measurements. Investigations of sandwich structures showed that the sensitivity decreased as a function of the number of membranes on top of the immobilized layer of active creatinine deaminase. It was thus shown that the sensitivity depends on the distance of diffusion of species from the sample solution through the membranes to the enzyme. Copyright © Taylor & Francis Group, LLC.

"Introduction Of Hydrogen Peroxide As An Oxidant In Flow Injection Analysis: Speciation Of Chromium(III) And Chromium(VI)"
Anal. Chim. Acta 1998 Volume 361, Issue 1-2 Pages 125-131
Jens E. T. Andersen*

Abstract: Hydrogen peroxode was used as an oxidant in flow injection analysis (FIA). The formation of gaseous components during the analysis was suppressed by maintaining the concentration of H2O2 <0.15% in 0.1 M NaOH. By this method, Cr(III) was oxidized online to Cr(VI) which was detected spectrophotometrically at 548 nm by complexation with 1,5-diphenylcarbazide (DPC). Linear responses were found for concentrations. <20 mg/l and the sensitivities obtained of the pure species were 0.0225±0.0015 L/mg for Cr(III) and 0.0420±0.0015 L/mg for Cr(VI). For the speciation of Cr(III) and Cr(VI), the anal. of both species was performed by treating them as mutual interferences. Thus, the total amt. of Cr species was measured by FIA and the total amount of Cr was measured by Graphite Furnace Atomic Absorption Spectrometry (GFAAS). The speciation was performed at concentrations. >6 mg/L which is suitable for online monitoring of e.g. waste waters.
Chromium(III) Chromium(VI) Waste Spectrophotometry Sample preparation Speciation Method comparison Process monitoring Interferences

"A Novel Method For The Filterless Preconcentration Of Iron"
Analyst 2005 Volume 130, Issue 3 Pages 385-390
Jens E. T. Andersen

Abstract: A novel method of analysis of iron by filterless pre-concentration is presented. This is the first example of efficient pre-concentration of a refractory transition metal where coprecipitation and columns were omitted. The method applies a manifold of flow injection analysis (FIA) to iron species that are pre-concentrated on the inner walls of a tubular reactor. It was found that the adsorption of iron species to the walls was particularly pronounced in reactors of nylon material and enrichment factors of 30-35 could be attained, as dependent on the length of the reactor and on the time of pre-concentration. In the pre-concentration step of the FIA accessory, the optimum efficacy was obtained when the acidity of the samples was adjusted by HCl to pH = 2.5 whereas the ammonia pre-concentration buffer should be kept alkaline at pH = 9.8. After being pre-concentrated on the tubular reactor, the iron species were eluted by hydrochloric acid and analyzed by flame atomic absorption spectrometry (FAAS). An unprecedented low limit of detection (LOD, 3?) of 1.8 ?g L -1 was thus obtained for the analysis of iron by FAAS, and the calibration line was linear up to 100 ?g L-1. A high sampling frequency of 40 per hour was obtained and the protocol allowed analysis of small amounts of iron in drinking water, in digested samples and in saline water. The major influence of interferences originated from ligands that are known to complex strongly to iron species. The method thus developed was uncomplicated in operation and it exhibited an excellent long-term stability and a high selectivity. Further, it was environmentally safe owing to production of non-toxic waste disposals. Equally high enrichment factors (EF) were obtained for Fe(II) and Fe(III), which is explained by the very low solubility product of both species. © The Royal Society of Chemistry 2005.