Concentrations Of Reactive Mn(Iii)-L And Mno2 In Estuarine And Marine Waters Determined Using Spectrophotometry And The Leuco Base, Leucoberbelin Blue

Details

• Journal Title:
  Talanta
• Personal Author:
  Jones, Matthew R. ; Luther, George W. ; Mucci, Alfonso ; Tebo, Bradley M.
• NOAA Program & Office:
  Sea Grant ; OAR (Oceanic and Atmospheric Research)
• Sea Grant Program:
  DELU (Delaware Sea Grant)
• Description:
  In terms of its oxidative strength, the MnO2/Mn2+ couple is one of the strongest in the aquatic environment. The intermediate oxidation state, manganese(III), is stabilized by a range of organic ligands (Mn(III)-L) and some of these complexes are also strong oxidants or reductants. Here, we present improved methods for quantifying soluble reactive oxidized manganese(III) and particulate reactive oxidized manganese at ultra-low concentrations; the respective detection limits are 6.7 nM and 7 pM (100-cm spectrophotometric path length) and 260 nM and 2.6 nM (1-cm path length). The methods involve a simple, specific, spectrophotometric technique using a water-soluble leuco base (leucoberbelin blue; LBB). LBB is oxidized by manganese through a hydrogen atom transfer reaction forming a colored complex that is stoichiometrically related to the oxidation state of the manganese, either Mn(III)-L or manganese(III,IV) oxides (MnOx). At the concentration of LBB used in this study, nitrite may be a minor interference, so we provide concentration ranges over which it interferes and suggest potential strategies to mitigate the interference. Unlike previous methods devised to quantify Mn(III)-L, which use ligand exchange reactions, the LBB oxidation requires an electron and therefore needs to physically contact manganese(III) for inner-sphere electron transfer to occur. The method for measuring soluble Mn(III)-L was evaluated in the laboratory, and LBB was found to be oxidized by an extensive suite of weak Mn(III)-L complexes, as it is by MnOx, but could not react with or reacted very slowly with strong Mn(III)-L complexes. According to the molecular structures of the Mn(III)-L complexes tested, LBB can also be used to qualitatively assess the binding strength of Mn(III)-L complexes based on metal-chelate structural considerations. The assays for soluble Mn(III)-L (membrane filtered) and particulate manganese oxides (trapped by membrane filters) were applied to the well-oxygenated estuarine waters of the Saguenay Fjord, a major tributary of the Lower St. Lawrence Estuary, and to Western North Atlantic oceanic waters, off the continental shelf, where there is an oxygen minimum zone (< 67% O2 saturation). The methods applied can be used in the field or onboard ships and provide important new insights into oxidized manganese speciation.
• Keywords:
  Leucoberbelin Blue (LBB) Manganese Speciation MnO2Mn(III)-L Seawater Spectrophotometry Manganese Speciation
• Source:
  Talanta 200: 91-99
• DOI:
  https://doi.org/10.1016/j.talanta.2019.03.026
• Document Type:
  Journal Article
• Funding:
  Grant no. NA14OAR4170087
• Rights Information:
  Accepted Manuscript
• Compliance:
  Library
• Main Document Checksum:
  urn:sha256:fa174526036d1030f5eb13f1f9f9d6ca9c580cd11f9da42236eec30952a484af
• Download URL:
  https://repository.library.noaa.gov/view/noaa/33085/noaa_33085_DS1.pdf
• File Type:
  [PDF - 931.24 KB ]