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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Constant M. G. van den Berg

Abbrev:
Van Den Berg, C.M.G.
Other Names:
Address:
Oceanography Laboratories, University of Liverpool, PO Box 147 Liverpool L69 3BX UK
Phone:
+44-151-794-4090
Fax:
+44-151-794-4099

Citations 5

"Monitoring Of Labile Copper And Zinc In Estuarine Waters Using Cathodic-stripping Chronopotentiometry"
Mar. Chem. 1991 Volume 34, Issue 3-4 Pages 211-223
C. M. G. van den Berg

Abstract: The sensitivity of cathodic-stripping chronopotentiometry was not affected by variations in salinity or by dissolved O, which rendered this technique suitable for the online automated determination of Cu and Zn in the Tamar estuary. The measurement rate was ~90 samples h-1 and the detection limits were 5 nM and 6 nM for Cu and Zn, respectively. The results agreed with the findings of previous studies. The online measurements eliminated the problem of sample contamination, provided a detailed picture of metal behavior in the estuary and elucidated local inputs. The technique is less sensitive than differential pulse cathodic-stripping voltammetry, but does not require sample filtration or deaeration, which facilitates its application to continuous-flow analysis. The sensitivity was not sufficient, however, to monitor Cu and Zn concentration. in uncontaminated seawater.
Copper Zinc Estuarine Sea Potentiometry Automation Method comparison Interferences Sensitivity

"Sequential Flow Analysis Coupled With ACSV For Online Monitoring Of Cobalt In The Marine Environment"
Fresenius J. Anal. Chem. 1997 Volume 358, Issue 6 Pages 703-710
Anne Daniel A, Alex R. Baker A, C. M. G. van den Berg

Abstract: The development of a compact instrument for on-line measurement of trace metals in seawater is described. The system is based on adsorptive cathodic stripping voltammetry (ACSV), and on the concept of sequential flow analysis, to perform on-line measurements with controlled perturbation of natural equilibria of the element. The design combines a low volume flow cell with a miniature solenoid pump and valves to achieve low power consumption. The flow segmentation is time-controlled and the detection step takes place in a well-defined part of the flow stream where reagent and sample occur mixed. The system was tested on the determination of cobalt in seawater but it is likely that the same technique can be used to determine other metals detectable by CSV. The determination range was 6-1050 pmol/L cobalt with a detection limit (3σ) of 6 pmol/L. The measurement rate was about 60 h-1. Comparative measurements were carried out using continuous flow analysis. The apparatus was used continuously on board a ship to determine the distribution pattern of cobalt in surface waters off the coast of California.
Cobalt Sea Voltammetry Voltammetry Sequential injection

"Determination Of Picomolar Levels Of Iron In Seawater Using Catalytic Cathodic Stripping Voltammetry"
Anal. Chem. 2001 Volume 73, Issue 11 Pages 2522-2528
Hajime Obata and Constant M. G. van den Berg

Abstract: A new procedure for the direct determination of picomolar levels of iron in seawater is presented. Cathodic stripping voltammetry (CSV) is preceded by adsorptive accumulation of the iron(III) -2,3-dihydroxynaphthalene (DHN) complex from seawater, containing 20 muM DHN at pH 8.0, onto a static mercury drop electrode, followed by reduction of the adsorbed species. The reduction current is catalytically enhanced by the presence of 20 mM bromate. Optimized conditions include a 60-s adsorption period at -0.1 V and a voltammetric scan using sampled de modulation at 10 Hz, In these conditions, a detection limit of 13 pM iron in seawater was achieved which can be lowered further by extending the adsorption time to 300 s. The new catalytic CSV method is similar to5 times more sensitive than existing CSV methods and was tested on samples from the Atlantic Ocean.
Preconcentration

"In-line Deoxygenation For Flow Analysis With Voltammetric Detection"
Anal. Chim. Acta 1998 Volume 377, Issue 2-3 Pages 229-240
Carlo Colombo and Constant M. G. van den Berg*

Abstract: Voltammetric detection of metals in natural waters suffers from interference by dissolved oxygen. We describe here a deoxygenation method suitable for flow analysis with detection by cathodic stripping voltammetry (FIA-CSV). The apparatus is based on the permeation of oxygen through semi-permeable tubing (silicone, Poreflon and others) into an oxygen-free chamber. Two methods of oxygen removal are proposed: in the first oxygen is removed physically from the chamber by flushing with nitrogen at a rate of 50 mL min-1; in the second oxygen is removed chemically by filling the chamber with an aqueous solution of a reducing agent (Na2SO3 or other compounds). At a fixed sample flow rate of 1 mL min-1, the length of the tubing is the main parameter which affects the deoxygenation efficiency, as it determines the residence time of the sample. 98% oxygen removal is achieved using 3 m tubing (36s residence time). A removal of 90% of oxygen (1 m tubing and 12 s residence time) is sufficient to obtain a background current similar to conventional (batch) voltammetric systems and reproducible metal (copper and cobalt) peak heights are obtained at low metal concentrations. This enables the determination of trace metals by flow analysis with voltammetric detection at concentration levels encountered in uncontaminated seawater.
Copper Cobalt Sea Voltammetry Silicone membrane

"A Flow Cell For Online Monitoring Of Metals In Natural Waters By Voltammetry With A Mercury Drop Electrode"
Anal. Chim. Acta 1997 Volume 346, Issue 1 Pages 101-111
Carlo Colombo, Constant M. G. van den Berg*, and Anne Daniel

Abstract: A flow-through detection cell is described for determining trace metals in nonpolluted seawater by cathodic-stripping voltammetry. The cell was constructed from cylindrical extruded acrylic drilled to give a flow channel of 1 cm x 0.7 mm (4 µL volume) and equipped with a hanging Hg drop electrode (0.46 mm i.d., 0.67 mm2), a Ag/AgCl reference electrode and a Pt wire auxiliary electrode. The detection cell was incorporated into a computer-controlled voltammetric system with a tangential flow filter, online UV digestion to destroy organic matter, a three-way switching value for the addition of reagents and standards and online deoxygenation. Filtered, UV-digested seawater (0.8 ml/min) merged with a reagent stream (0.135 ml/min) to produce a measurement solution containing 0.45 M NaNO2, 25 mM NH3/NH4Cl and 4.5 µM-1,2-cyclohexanedione dioxime (nioxine) of pH 9. After deoxygenation, the voltammetric measurement was performed with an accumulation potential of -0.75 V for 30 s, a 5 s equilibration period and a stepped potential scan to -1.25 V. A linear response was obtained for up to 550 pM-Co, the detection limit was 5.4 pM and the RSD for 29.6 pM-Co was 6%. The analysis rate was 40-60 samples/h. The method was verified by analyzing certified seawater.
Cobalt Sea Voltammetry Electrode Sample preparation Reference material UV reactor Detector Flowcell Photochemistry