University of North Florida
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Contact Info

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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Francisco J. Krug

Abbrev:
Krug, F.J.
Other Names:
Francisco Jose Krug
Address:
Centro de Energia Nuclear na Agricultura, Universidade de Sao Paulo, P.O. Box 96, CEP 13400-970 Piracicaba-SP Brazil
Phone:
+55-19-429-4646
Fax:
+55-19-429-4610

Citations 5

"Online Coupling Of Electrochemical Preconcentration In Tungsten Coil Electrothermal Atomic Absorption Spectrometry For Determination Of Lead In Natural Waters"
Spectrochim. Acta B 1999 Volume 54, Issue 8 Pages 1155-1166
Fernando BarbosaJr, Francisco J. Krug and Éder C. Lima

Abstract: A flow injection system was coupled to a W coil electrothermal atomizer (150 W) for online separation and pre-concentration. of Pb based on its electrochemical reduction on the atomizer surface. The electrochemical cell was built inside the furnace using a Pt flow-through anode and the atomizer itself as the flow-through cathode. The manifold and the W coil power supply were controlled by a computer running a program written in Visual Basic, used in synchronization with the original software of the atomic absorption spectrometer. The flow-through anode (50 mm long, 0.7 mm inside diameter) was inserted in tip of the autosampler arm by replacing the last section of the polytetrafluoroethylene sample delivering tube. The W coil atomizer and counter electrode were easily connected to a DC power supply. An enrichment factor of 25 was obtained for Pb after a 120 s electrodeposition for a sample flowing at 1.0 mL/min. The method detection limit was 0.2 µg/L Pb and the relative standard deviation was <5% (n = 10 for 5 µg/L Pb). Up to 2% (m/v) NaCl or KCl and 5% (m/v) CaCl2 or MgCl2 did not interfere with separation and atomization of 5 µg/L Pb.

"Separation And Preconcentration By Flow Injection Coupled To Tungsten-coil Electrothermal Atomic Absorption Spectrometry"
Spectrochim. Acta B 1996 Volume 51, Issue 14 Pages 1925-1934
M&aacute;rcia M. Silva, Francisco J. Krug*, Pedro V. Oliveira, Joaquim A. N&oacute;brega, Boaventura F. Reis and Daniel A. G. Penteado

Abstract: Owing to the uncertain pyrolysis performance of the W-coil atomizer, a flow injection preseparation-pre-concentration system was developed, diagrams of which are presented. A 16 µL SPE microcolumn (Chelex-100) was mounted on the tip of the arm of a Perkin-Elmer GTA-96 ETAAS autosampler, which delivered 20 µL portions of the eluate (eluent 2 M HCl) to the W coil [protected by Ar/H2 (9:1)]. For Pb (model analyte) retained from sample solution flowing at 3 ml/min for 1 min, the enrichment factor was 64, the detection liwas 75 ng/l and the RSD (n = 10) at 2 µg/l was
Lead Spectrophotometry Chelex Preconcentration Apparatus Column

"In Situ Trapping Of Selenium Hydride In Rhodium-coated Tungsten Coil Electrothermal Atomic Absorption Spectrometry"
J. Anal. At. Spectrom. 2002 Volume 17, Issue 4 Pages 382-388
Fernando Barbosa Jr., Samuel Simi&atilde;o de Souza and Francisco J. Krug

Abstract: A flow injection hydride generation manifold was coupled to a tungsten coil electrothermal atomizer for in situ collection of selenium. This strategy exploits selenium hydride trapping onto a double-layer coiled tungsten filament coated with rhodium. The hydride flows through a capillary quartz tube (20 mm long x 1.3 mm od x 0.5 min id) positioned 1 mm from the modified tungsten coil surface. The capillar, can be either inserted in the tip of the autosampler arm by replacing the last section of the PTFE sample delivery tube, or can be fixed in a silicone stopper. Signal stability and repeatability were observed over 300 atomization cycles using 300 µg Rh thermally reduced over the tungsten coil surface. The coil lifetime was extended to at least 2000 firings at 2300 C. An enrichment factor of 200 was obtained for selenium after 60 s of hydride trapping for a sample flowing at 2.5 mL min-1. The detection limit, based on three times the standard deviation of the blank, was 50 ng L-1 Se with a sample throughput of 40 h-1. Method accuracy was evaluated by analyzing ordinary mineral water using the proposed method and hydride generation atomic fluorescence spectrometry and water reference materials from the National Institute of Standards and Technology (SRM 1640 Trace Elements in Natural Water) and from High-purity Standards (Trace Metals in Drinking Water). No statistical differences were found between the values encountered by both techniques and the certified values by applying a t-test at the 95% confidence level.

"The Use Of A W-Rh Permanent Modifier For Direct Determination Of Bismuth In Urine And Whole Blood By Electrothermal Atomic Absorption Spectrometry"
J. Anal. At. Spectrom. 2001 Volume 16, Issue 8 Pages 842-846
Fernando Barbosa Jr, Eder C. Lima, Renato A. Zan&atilde;o and Francisco J. Krug

Abstract: The direct determination of bismuth in urine and whole blood samples is proposed by graphite furnace atomic absorption spectrometry. The pyrolytic integrated platform of the THGA tube was coated with 250 jig W+200 µg Rh to increase the tube lifetime. Urine samples were diluted (1 + 1 v/v) and blood samples (1 + 4 v/v) in a solution containing 1.0% v/v HNO3 + 0.2% Triton X-100, and 20 µL of the resulting dilute samples were delivered into the W-Rh modified platform together with 10 µL of 10 mg L-1 Rh solution. After 350 firings a new coating was made. The combined use of Rh solution with the W-Rh coating was decisive for increasing the maximum pyrolysis temperature of blood and urine bismuth up to 1100°C. With this approach the tube lifetime increased by 80% and re-calibrations were minimised when compared to a Pd+Mg conventional modifier. The detection limits (n = 20) were 3.3 µg L-1 and 8.4 µg L-1 for urine and whole blood, respectively, and the characteristic mass was 49.0 pg using standard THGA. The accuracy of the proposed method was verified by comparing the results with the decomposed sample solutions. No statistical differences were found by the paired t-test at the 99% confidence level.

"Isothermal Distillation In Flow Injection Analysis. Determination Of Total Nitrogen In Plant Material"
Anal. Chim. Acta 1979 Volume 109, Issue 1 Pages 45-54
E. A. G. Zagatto, B. F. Reis, H. Bergamin F and F. J. Krug

Abstract: An isothermal distilaltion unit is incorporated in flow injection systems. The influence of surfactant, flow rates, alkalinity, ionic strength, collector stream pH, reagent concentration, and sample volume in NH3 distillation are discussed. A method for the determination of total N in plant digests employing Nessler reagent is proposed. This method, based on merging zones approach, is characterized by a sampling rate of 100 samples/h, a precision >3%, a reagent consumption of only 100 µL/sample, and virtually no base-line drift. The results agree with those obtained with the indophenol blue colorimetric method. The incorporation of isothermal distillation in flow systems with potentiometric measurement is also described.
Nitrogen, total Plant Potentiometry Spectrophotometry Isothermal distillation Merging zones Optimization Method comparison