The determination of iron in seawater using catalytic cathodic stripping voltammetry

Abstract

The sensitivity of the determination of iron in natural waters, including seawater, using cathodic stripping voltammetry (CSV) with adsorptive collection of complexes with 1-nitroso-2-naphthol is greatly enhanced by catalytic reoxidation in the presence of hydrogen peroxide. The limit of detection is lowered to 0.16 nM Fe (using an adsorption time of 60 s) and further to 0.03 nM Fe by increasing the adsorption time to 10 min. Interference from an increase in the background current, brought about by catalysis of the hydrogen evolution, is overcome by addition of an anionic surfactant (sodium dodecyl sulfate (SDS)). Optimal conditions include a hydrogen peroxide concentration of 1.8 mM and 5 ppm SDS. Procedures to p u r e the reagents from contaminant levels of iron are described. The method is successfully applied to certified seawater and samples from the North Atlantic.

Detection of Iron(III)-Binding Ligands Originating from Marine Phytoplankton Using Cathodic Stripping Voltammetry

“…The iron peak reduction current of the control was observed at -550 mV, which is in agreement with previous studies. 28,29 On the other hand, the peak currents in the phytoplankton filtrates were shifted to a lower potential (Fig. 1).…”

“…The term "labile iron" is defined in this paper as the iron which reacts with the added NN within 5 h. To measure the labile iron, we revised a CLE/ACSV method based on previous studies. 1,2,28,29 Under a class-100 clean condition, 9.5 ml aliquots of a 3.5% NaCl solution were pipetted into FEP-Teflon voltammetric cell cups, and premixed with 0.5 ml of samples containing iron(III)-binding ligands, 154 µl of 0.65 M HEPES buffer (pH 8) and 100 µl of a 1 mM NN stock solution. Iron(III) stock solutions were added to the cups, yielding concentrations from 0 to 40 nM, and the added iron was allowed to equilibrate with the iron(III)-binding ligands for 5 h at room temperature.…”

“…[1][2][3][4][28][29][30] Two different competitive ligands, 1-nitroso-2-naphthol 1,2 and salicylaldoxime, 3 were commonly used for iron(III) speciation by CLE/ACSV. Since the measurements have been extensively studied for the speciation and reactivity of organically complexed iron(III), 1-nitroso-2-naphthol was selected as the competitive ligand in this study.…”

“…It is reported that the reduction current of ACSV with 1-nitroso-2-naphthol was enhanced by the addition of oxidizing agents and surfactants, such as H2O2, bromate and sodium dodecyl sulfate. 28,29 In choosing the analytical condition, particular emphasis was placed on keeping the chemical forms of the iron(III)-binding ligands throughout the procedure. Therefore, voltammetric scans were carried out at pH 8.0 without oxidizing agents and surfactants, in which the measurements of ACSV were sufficiently sensitive to determine the nM levels of iron(III) in sample solutions.…”

A Novel Catalytic Adsorptive Stripping Voltammetric Method of Iron Determination as Its 1,2‐Cyclohexanedione Dioxime Complex

“…The catalytic adsorptive stripping voltammetry (CAdSV) methods, which are based on the adsorptive accumulation of metal complex on the hanging mercury drop electrode (HMDE), followed by a catalytic reaction, have been successfully applied for ultratrace metal analysis [10 ± 12]. The catalytic amplification of the polarographic [13] and AdSV iron signal is observed in the presence of oxidizing agents such as: H 2 O 2 [14,15], BrO À 3 [16,17], ClO À 2 [13], NO À 2 [18]. The extremely high sensitivity of the CAdSV procedures enabled the determination of pM iron concentration level in oceanic water samples [19].…”