title: Quantification of pH-dependent speciation of organic compounds with spectroscopy and chemometrics.
abstract: Fluorescence and UV/Vis spectra of aqueous solutions with numerous organic compounds are a superposition of single spectra of the chemical species present. Thus, an isolation of individual spectra with chemometrics is required for their quantification. We investigated UV/Vis spectra and fluorescence excitation-emission matrices of vanillic acid, salicylic acid, phenoxyacetic acid and phthalic acid with positive matrix factorization (PMF) and non-negativity constrained parallel factor analysis (PARAFAC) in combination with the law of mass action. In consideration of the pH-dependent speciation of organic acids, we first reconstructed the pH-specific spectra of each compound. Using these spectra as known components in a constrained algorithm, we could successfully quantify species of multiple compounds and reconstruct the solution pH. In addition, we estimated the uncertainty of reconstructed spectra and concentrations in order to assess the most probable number of components for PMF/PARAFAC. Therefore, we could derive a framework to reconstruct the number of relevant species and their individual concentration present in spectroscopic data of aqueous solutions containing multiple organic compounds.
authors.affiliation: Department of Hydrogeology, Institute for Geosciences, Friedrich-Schiller-University Jena, Burgweg 11, 07749 Jena, Germany. Electronic address: Thomas.Ritschel@uni-jena.de.
authors.forename: Thomas
authors.initials: T
authors.lastname: Ritschel
authors.affiliation: Department of Hydrogeology, Institute for Geosciences, Friedrich-Schiller-University Jena, Burgweg 11, 07749 Jena, Germany.
authors.forename: Kai Uwe
authors.initials: KU
authors.lastname: Totsche
mesh_terms: D000085:Acetates / Q000032:analysis / Q000737:chemistry; D004463:Ecology / Q000379:methods*; D005163:Factor Analysis, Statistical; D006863:Hydrogen-Ion Concentration; D009930:Organic Chemicals / Q000032:analysis* / Q000737:chemistry; D010795:Phthalic Acids / Q000032:analysis / Q000737:chemistry; D020156:Salicylic Acid / Q000032:analysis / Q000737:chemistry; D012996:Solutions; D013050:Spectrometry, Fluorescence / Q000379:methods*; D013056:Spectrophotometry, Ultraviolet / Q000379:methods*; D014641:Vanillic Acid / Q000032:analysis / Q000737:chemistry
chemical_list: D000085:Acetates; D009930:Organic Chemicals; D010795:Phthalic Acids; D012996:Solutions; C032279:phthalic acid; D014641:Vanillic Acid; D020156:Salicylic Acid; C415326:phenoxyacetic acid
keywords: Environmental tracer; Number of components; Organic acid; Parallel factor analysis (PARAFAC); Positive matrix factorization (PMF)