University of North Florida
Browse the Citations

Contact Info

Stuart Chalk, Ph.D.
Department of Chemistry
University of North Florida
Phone: 1-904-620-1938
Fax: 1-904-620-3535
Website: @unf

View Stuart Chalk's profile on LinkedIn


Citations 8

"A Comparison Between ICP-MS And AFS Detection For Arsenic Speciation In Environmental Samples"
Talanta 2000 Volume 51, Issue 2 Pages 257-268
Jose Luis Gómez-Ariza, Daniel Sánchez-Rodas, Inmaculada Giráldez and Emilio Morales

Abstract: Performances of two atomic detectors, Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) arid Atomic Fluorescence Spectrometry (AFS) have been compared for arsenic speciation in environmental samples. Instrumental couplings, based on the use of high performance liquid chromatography (HPLIC), hydride generation (HG), and the two atomic detectors were used for the speciation of arsenite, arsenate, dimethylarsinic acid and monomethylarsonic acid. Optionally, arsenobetaine was also determined using on-line ultraviolet (UV) photooxidation. The detection limits ranging from 0.1 to 0.3 µg L-1 (as As) and the precision > 10% RSD obtained with HPLC-(UV)-HG-AFS were comparable with those obtained with HPLC-(UV)-HG-ICP-MS. Both instrumental coupling were applied to the NRCC-TORT-1 and several environmental samples, such as seawater, freshwater, sediments, bivalves and bird eggs, taken from two areas with different degrees of pollution. No influence of the sample matrix was observed on the results using external calibration and standard additions met:hods, for both coupled techniques.
Arsenate ion Arsenite Arsenoβine Dimethylarsinic acid monomethylarsonic acid Fluorescence Mass spectrometry Sample preparation HPLC Speciation Extraction Method comparison Reference material Interferences Standard additions calibration Optimization

"On-line Preconcentration System For Lead Determination In Seafood Samples By Flame Atomic Absorption Spectrometry Using Polyurethane Foam Loaded With 2-(2-benzothiazolylazo)-2-p-cresol"
Anal. Chim. Acta 2001 Volume 441, Issue 2 Pages 281-289
Valfredo A. Lemos and Sérgio L. C. Ferreira

Abstract: In the present paper, an on-line system for enrichment and determination of lead is proposed. It is based on the chemical sorption of lead(II) ions on a minicolumn packed with polyurethane foam loaded with 2-(2-benzothiazolylazo)-2-p-cresol (BTAC) reagent. After pre-concentration, lead(II) ions are eluted by 0.10 mol L-1 hydrochloric acid solution and determined directly by flame atomic absorption spectrometry (FAAS). Chemical and flow variables as well as effect of other ions were studied. The results demonstrated that lead could be determinate with an enrichment factor of 26 for a sample volume of 7.0 mL and pre-concentration time of 1 min. The detection limit (3 s) was 1.0 µg L-1 and the precision (assessed as the relative standard deviation) reached values of 6.0-0.7% in lead solutions of 10^-500 µg L-1 concentration, respectively. The enrichment factor and the detection limit can be further improved by increasing pre-concentration time without degradation in the efficiency due to the favorable kinetics and low hydrodynamic impedance of the present system. Achieved sampling frequency was 48 samples per hour. The effect of another ions in concentrations agreeing with biological samples was studied. It was found that the proposed procedure has necessary selectivity for lead determination in seafood and other biological samples. The accuracy was confirmed by analysis of the followings certified reference materials: fish tissue IAEA, lobster hepatopancreas NRCC TORT-1 and citrus leaves NIST 1572. Recoveries of spike additions (0.2 or 1.0 µg g-1) to several seafood samples were quantitative (90-107%). These results proved also that the procedure is not affected by matrix interferences and can be applied satisfactorily for lead determination in samples of shrimp, oyster, crab, fish and mussel contaminated by it.
Lead Spectrophotometry Preconcentration Interferences Amberlite Polyurethane foam Solid phase extraction

"Continuous-flow Microwave-assisted Digestion Of Environmental Samples Using Atomic Spectrometric Detection"
J. Anal. At. Spectrom. 1995 Volume 10, Issue 11 Pages 981-986
Ralph E. Sturgeon, Scott N. Willie, Brad A. Methven, Joseph W. H. Lam and Henryk Matusiewicz

Abstract: A continuous-flow microwave-assisted digestion technique was tested with a view to the evaluation of its effectiveness for decomposition of environmental samples. A CEM SpectroPrep system was used at moderate powers and pressures of up to 2413 kPa to perform on-line digestion of slurried samples of biological tissues (0.5% m/v) and marine sediment (1% m/v). The efficiency of oxidation of biological matrices, as characterized by the residual carbon content of the solutions, was 64%. Recovery of trace elements averaged 90±1% and was accommodated with the use of suitable internal standards. Accuracy was verified by analysis of certified reference materials from the National Research Council of Canada, marine sediment BCSS-1 and lobster hepatopancreas tissue LUTS-1. Precision of measurement, as reflected in the determination of the trace metal content in replicate solutions, using a variety of atomic spectrometric techniques, was better than 1% RSD (relative standard deviation).
Metals Sample preparation Spectrophotometry Microwave Online digestion

"Determination Of Mercury In Filtered Seawater By Flow Injection With Online Oxidation And Atomic Fluorescence Spectrometric Detection"
J. Anal. At. Spectrom. 1996 Volume 11, Issue 7 Pages 511-514
Martin J. Bloxham, Steve J. Hill and Paul J. Worsfold

Abstract: A flow injection (FI) atomic fluorescence method incorporating an online bromide-bromate oxidation step to determine mercury in filtered seawater samples at the ng L-1 level is described. A heated reaction coil was incorporated in the FI manifold to increase the conversion of organic mercury into inorganic mercury(II) chloride from 50 to approaching 100%. Detection limits (3s) for mercury(II) chloride and methylmercury chloride were 25 and 23 ng L-1 Hg, respectively. The FI manifold could also be used to determine the total mercury concentration in biological materials and was validated by analyzing the CRM TORT-1 Lobster Hepatopancreas. Good agreement with the certified (330±60 µg l-1) value was achieved (353±64 pg l-1). The analysis of coastal water samples from Sutton Harbour, Plymouth, showed that mercury levels ranged from 24±5 to 54±10 ng l-1.
Mercury(II) Fluorescence Reference material

"Determination Of Organomercury In Biological Reference Materials By Inductively Coupled Plasma Mass Spectrometry Using Flow Injection Analysis"
Anal. Chem. 1988 Volume 60, Issue 23 Pages 2587-2590
Diane Beauchemin, K. W. M. Siu, and S. S. Berman

Abstract: Samples of DORM-1 dogfish muscle and TORT-1 lobster hepatopancreas were acidified with HCl and extracted with toluene, and the organomercury compounds were back-extracted into aqueous cysteine acetate solution. Extracts were analyzed by isotope-dilution ICP-MS with use of a flow injection technique and a 100 µL sample loop in order to overcome interference caused by the presence of 4% of Na in the extracts. Results were compared with those obtained by GC - ECD. Methylmercury is the only significant organomercury compound present in DORM-1.
Ethylmercury Methylmercury ion Phenylmercury Clinical analysis Mass spectrometry Mass spectrometry Method comparison Reference material Interferences Speciation

"Determination Of Arsenic And Selenium By Hydride Generation Atomic Absorption Spectrometry Using A Gas-liquid Separator And A Dehydration Trap"
Microchem. J. 1996 Volume 53, Issue 1 Pages 18-25
Hisatake Narasaki and Jun-Yan Cao

Abstract: Biological material (0.25 g) was allowed to stand overnight in 3 mL concentrated HNO3, 0.5 mL concentrated H2SO4 and 1 mL 60% HClO4 were added and the mixture was digested under low heat until the fumes of HClO4 subsided. The digests, including siliceous residues, were transferred to a Pt dish with water and evaporated to 2 mL. The residues were dissolved with 5 mL 46% HF, 1 mL 9 M H2SO4 was added and the solution was concentrated to 2 mL. The pH was adjusted to 3.5 with 1 M NH3 and applied to a SPE column (35 cm x 10 mm i.d.) packed with 10 cm Chelex 100 chelating ion-exchange resin and the column was washed with 2 x 10 mL water. For the analysis of As; the column effluents were diluted to 100 mL with water and a 10 mL portion was mixed with 5 mL 6 M HCl. Portions of both acid solutions were introduced into the flow injection hydride generation system (schematic shown) and mixed with a stream of 2% sodium tetrahydroborate(III) solution in a Pyrex mixing coil (16 cm x 2 mm i.d.). The hydride generated was collected in a gas-liquid separator, dehydrated in a dehydration trap and swept into an electrically heated furnace with a carrier stream of N2 (2.5 l/min) by manipulating electromagnetic relays and timers (operating details given). The atomized As and Se species were detected at 193.7 and 196 nm, respectively, by AAS. The detection limits were 0.6 and 1 ng/ml, respectively. Tolerance levels to 10 foreign ions are listed. The method was applied to the analysis of five NIST Standard Reference materials (listed). Results agreed well with certified values.
Arsenic Selenium Spectrophotometry Reference material Chelex

"Determination Of Selenium By Flow-injection Analysis Based On The Selenium(IV)-catalyzed Reduction Of 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium Bromide"
Anal. Sci. 1991 Volume 7, Issue 1 Pages 103-107

Abstract: Sample solution was mixed with NaOH (to pH 7) and 0.1 M phosphate buffer solution (pH 7) containing 12 mM bathocuproine disulfate and the mixture was injected into a carrier solution of 0.1 M phosphate buffer solution (0.2 mL min-1) and through a column (5 cm x 4.6 mm) of Chemcasorb 3-ODS-H operated at 40°C. The eluate was mixed with 7.3 mM dithiothreitol and 3-[4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide and the absorbance of the solution was measured at 565 nm. Analysis time was 8 min. The calibration graph was rectilinear for 1.3 pmol to 1.2 nmol Se (IV) and the coefficient of variation was 2.2%. The method was applied in the analysis of lobster refrence material, recovery was 103% for 5 µg mL-1 of Se and no interference was present.
Selenium Spectrophotometry Buffer Catalysis Column Heated reaction Interferences Solid phase reagent

"Optimized Microwave Digestion Procedure For Cadmium Analysis Of Mussel Samples"
Analusis 1998 Volume 26, Issue 7 Pages 261-263
M.C. Yebra and M.F. Enríquez

Abstract: A simple and rapid acid sample digestion method by microwave heating in high-pressure teflon bombs is reported for the determination of cadmium in mussels by flame atomic absorption spectrometry (FAAS) coupled online with a flow injection pre-concentration system. Tests concerning the digestion time, the power of the microwaves and the amt. of nitric acid were studied with the National Research Council of Canada lobster hepatopancreas marine (Tort-1) as certified reference material. Using 2 min of digestion time and 2 mL of nitric acid, the complete dissolution of 0.2 g of freeze-dried sample is possible. The anal. results, obtained with calibration graph as well as by the standard addition method, were agreed well with the certified value of the reference material. This procedure was applied to the determination of cadmium in mussel samples from estuaries in Galicia, Spain.
Cadmium Sample preparation Spectrophotometry Reference material Preconcentration Standard additions calibration