Comparison of Alternate Reactants for pM Level Cobalt Analysis in Seawater by the Use of Catalytic Voltammetry

Abstract

The analysis of Cobalt (Co) at low pM concentrations in seawater with Adsorptive Cathodic Stripping Voltammetry involves high concentrations of sodium nitrite (NaNO2) to enhance the signal in an electrocatalytic reaction. In this study we found three substitutes for NaNO2 that critically affected the sensitivity. Optimisation of a method with potassium bromate (KBrO3) resulted in an excellent detection limit (0.9 pM) after a 90 s adsorption period. Reactant concentration and consumption were 10× reduced compared to protocols with NaNO2 and reagent blanks were lower. Accuracy and precision were verified with SAFe intercalibration standards and the method was applied using open ocean seawater samples. The reaction mechanism is discussed and differences to NaNO2 are shown.

Dissolved cobalt speciation and reactivity in the eastern tropical North Atlantic

“…Accuracy and precision of the method were evaluated with the GEOTRACES intercalibration samples SAFe S (intercalibration North Pacific 2004, surface seawater) and SAFe D2 (intercalibration North Pacific 2004, 1000 m). The results for SAFe S (7.1 ± 1.1 pM, n = 10) and SAFe D2 (44.9 ± 2.4 pM, n = 10) were in good agreement with the consensus values (SAFe S: 4.8 ± 1.2 pM; SAFe D2: 45.7 ± 2.9 pM; http://www.geotraces.org/science/ intercalibration/322-standards-and-reference-materials) as previously reported (Baars and Croot, 2011).…”

“…H 2 O 2 was added to a concentration of 200 μM and samples were then UV digested for 3 h by placing them in a circular setup around a central UV source (Pen-Ray, UVP). Analysis proceeded after cooling to room temperature (~1 h) by catalytic AdCSV as described previously (Baars and Croot, 2011). Briefly, the UV digested samples were transferred into a cleaned Teflon cell cup and buffered by addition of a NH 3 /NH 4 Cl buffer (0.11 M, pH = 8.7 ± 0.1).…”

“…In this work, we complement the classical thermodynamicequilibrium Co titration approach by evaluation of Co ligand-exchange kinetics in samples collected in the eastern tropical North Atlantic using a highly sensitive catalytic AdCSV method (Baars and Croot, 2011). In addition, we assess the presence and reducibility of dissolved Co(III) in seawater using ascorbate as a reductant.…”

Quantification of Iron in Seawater at the Low Picomolar Range Based on Optimization of Bromate/Ammonia/Dihydroxynaphtalene System by Catalytic Adsorptive Cathodic Stripping Voltammetry

“…Hydroxylamine was recently shown to be a good catalytic reagent. 26 However, the formation of these oxidation products can be discarded, as none of them could be detected in UV-digested seawater by UV−vis spectrophotometry at pHs 8 and 9 (see ref 27 for the UV− vis spectra of these species). The possible transformation of DHN caused by the reported slow oxidation of DHN to a pink byproduct at a natural pH may be also ruled out.…”

Highly Sensitive and Selective Adsorptive Stripping Voltammetric Method Employing a Lead Film Screen‐printed Electrode for Determination of Cobalt as its Nioximate Complex

“…two orders of magnitude lower than that of Hg(II) [15].T hesee lectrodes have mostly been utilized for the anodic stripping voltammetric determination of Pb,C d, Zn, Tl;h owever, cases of adsorptives tripping voltammetric (AdSV) quantification of some metals,m ostly Ni and Co,a tt hese film electrodes have also been reported [6,13,14,16,17].I np articular, lead film electrodes deposited in-situ at the glassy carbon (GC) support offer outstanding performance in terms of selectivity and sensitivity in AdSV determinationo fs ome metals,s uch as Ni, Co [13,14,[18][19][20] TheA dSVp rocedures utilizingt he dioximate complexes belong to the most sensitivea nd selective analytical methodso fC oa nd Ni determination [ 6,24].A mong them, the method with dimethylglyoxime (DMG) is commonly used as the standard procedure [25,26].H owever, in the case of Co,t he AdSV method with nioxime [27], and especially its catalytic version with nioximea nd nitrite [6,24,[28][29][30][31][32],a ppear to be the mosts ensitive.I ndependently of the voltammetric mode used, the AdSV response of Co(II) in the presence of nioximei st wo to five times highert han that for DMG [27,28].T herefore,t he nioximel igand proved to be very effective for the quantificationo fu ltratrace levels of Co in ocean water using AdSV [27] and catalytic AdSV in variousm aterials at the mercurya nd otherm etallicf ilm electrodes [6,18,19,24,[28][29][30][31][32].I ts hould also be mentioned that Baars and Croot have recently founda nother extremely sensitive CAdSV method of Co(II) determination exploiting bromate instead of nitrite as an oxidant [ 33,…”