title: Cathodic pseudopolarography: a new tool for the identification and quantification of cysteine, cystine and other low molecular weight thiols in seawater.
abstract: Thiols are compounds of paramount importance in the cellular metabolism due to their double detoxifying role as radical scavengers and trace metal ligands. However, we have scarce information about their extracellular cycling as limited data are available about their concentration, stability and speciation in the aquatic medium. In natural waters, they form part of the pool of reduced sulfur substance (RSS) whose presence has been documented by voltammetric and chromatographic methods. Traditional use of cathodic stripping voltammetry (CSV) for the analysis of RSS could only give an overall concentration due to the coalescence of their CSV peaks. Recently, it has been shown that the use of multiple deposition potentials could take voltammetry of RSS to a higher level, permitting the identification and quantification of the mixtures of RSS despite showing as a single coalescent peak. Here, due to its similarity with classical pseudopolarography, we propose to rename this analytical strategy as cathodic pseudopolarography (CP) and we present for the first time its use for the analysis of mixes of low molecular weight thiols (LMWT) at the nanomolar level. Despite limitations caused by the identical behavior of some LMWT, the CP allowed to isolate the contribution of cysteine and cystine from a coalescent signal in LMWT mixtures. Sample handling with clean protocols allowed the direct determination of the cystine:cysteine ratio without sample modification. Finally, we show the application of CP to identify LMWT in seawater samples extracted from benthic chambers and suggest future applications in other areas of environmental electroanalysis.
authors: FI-TRACE, Departamento de Química, Universidad de las Islas Baleares, Palma, Balearic Islands 07122, Spain. Electronic address: luis.laglera@uib.es.
authors: Luis M
authors: LM
authors: Laglera
authors: FI-TRACE, Departamento de Química, Universidad de las Islas Baleares, Palma, Balearic Islands 07122, Spain.
authors: Javier
authors: J
authors: Downes
authors: Department of Ecotoxicology, Ecofisiology and Biodiversity of Aquatic Systems, ICMAN (CSIC), Campus Universitario Río San Pedro, Puerto Real, Cádiz 11510, Spain; Department of Global Change Research. Mediterranean Institute for Advanced Studies, IMEDEA (CSIC-UIB), Miguel Marques 21, Balearic Islands 7190, Spain.
authors: Antonio
authors: A
authors: Tovar-Sánchez
authors: Università degli Studi dell'Insubria, Dipertimento di Scienza e Alta Tecnologia, via Valleggio 11, Como 22100, Italy.
authors: Damiano
authors: D
authors: Monticelli
mesh_terms: D003300:Copper / Q000737:chemistry; D003545:Cysteine / Q000032:analysis*; D003553:Cystine / Q000032:analysis*; D004492:Edetic Acid / Q000737:chemistry; D055664:Electrochemical Techniques / Q000379:methods*; D008522:Mediterranean Sea; D008970:Molecular Weight; D011048:Polarography / Q000379:methods*; D012623:Seawater / Q000032:analysis* / Q000737:chemistry; D013438:Sulfhydryl Compounds / Q000032:analysis*; D013457:Sulfur Compounds / Q000032:analysis / Q000737:chemistry
chemical_list: D013438:Sulfhydryl Compounds; D013457:Sulfur Compounds; D003553:Cystine; D003300:Copper; D004492:Edetic Acid; D003545:Cysteine
keywords: Cathodic pseudopolarography; Cystine; Reduced sulfur substances; Seawater; Thiols; Voltammetry