Merck
  • Inicio
  • Resultados de la búsqueda
  • Combination of a Copper-Ion Selective Electrode and Fluorometric Titration for the Determination of Copper(II) Ion Conditional Stability Constants of Humic Substances.

Combination of a Copper-Ion Selective Electrode and Fluorometric Titration for the Determination of Copper(II) Ion Conditional Stability Constants of Humic Substances.

Applied spectroscopy (2015-12-10)
Juan Chen, Hao Chen, Xing-wen Zhang, Kun Lei, Jonathan E Kenny
RESUMEN

A fluorescence quenching model using copper(II) ion (Cu(2+)) ion selective electrode (Cu-ISE) is developed. It uses parallel factor analysis (PARAFAC) to model fluorescence excitation-emission matrices (EEMs) of humic acid (HA) samples titrated with Cu(2+) to resolve fluorescence response of fluorescent components to Cu(2+) titration. Meanwhile, Cu-ISE is employed to monitor free Cu(2+) concentration ([Cu]) at each titration step. The fluorescence response of each component is fit individually to a nonlinear function of [Cu] to find the Cu(2+) conditional stability constant for that component. This approach differs from other fluorescence quenching models, including the most up-to-date multi-response model that has a problematic assumption on Cu(2+) speciation, i.e., an assumption that total Cu(2+) present in samples is a sum of [Cu] and those bound by fluorescent components without taking into consideration the contribution of non-fluorescent organic ligands and inorganic ligands to speciation of Cu(2+). This paper employs the new approach to investigate Cu(2+) binding by Pahokee peat HA (PPHA) at pH values of 6.0, 7.0, and 8.0 buffered by phosphate or without buffer. Two fluorescent components (C1 and C2) were identified by PARAFAC. For the new quenching model, the conditional stability constants (logK1 and logK2) of the two components all increased with increasing pH. In buffered solutions, the new quenching model reported logK1 = 7.11, 7.89, 8.04 for C1 and logK2 = 7.04, 7.64, 8.11 for C2 at pH 6.0, 7.0, and 8.0, respectively, nearly two log units higher than the results of the multi-response model. Without buffer, logK1 and logK2 decreased but were still high (>7) at pH 8.0 (logK1 = 7.54, logK2 = 7.95), and all the values were at least 0.5 log unit higher than those (4.83 ~ 5.55) of the multi-response model. These observations indicate that the new quenching model is more intrinsically sensitive than the multi-response model in revealing strong fluorescent binding sites of PPHA in different experimental conditions. The new model was validated by testing it with a mixture of two fluorescing Cu(2+) chelating organic compounds, i.e., l-tryptophan and salicylic acid mixed with one non-fluorescent binding compound oxalic acid titrated with Cu(2+) at pH 5.0.

MATERIALES
Referencia del producto
Marca
Descripción del producto

Sigma-Aldrich
Salicylic acid, BioXtra, ≥99.0%
Sigma-Aldrich
Sodium hydroxide solution, 1.0 N, BioReagent, suitable for cell culture
Sigma-Aldrich
Salicylic acid, suitable for plant cell culture
Sigma-Aldrich
Sodium nitrate, BioUltra, ≥99.0% (T)
Sigma-Aldrich
Oxalic acid, puriss. p.a., anhydrous, ≥99.0% (RT)
Sigma-Aldrich
Salicylic acid, meets analytical specification of Ph. Eur., BP, USP, 99.5-100.5% (calc. to the dried substance)
Sigma-Aldrich
Sodium nitrate, ≥99.0%, suitable for plant cell culture
Sigma-Aldrich
Sodium nitrate, BioXtra, ≥99.0%
Sigma-Aldrich
Salicylic acid, ACS reagent, ≥99.0%
Sigma-Aldrich
Oxalic acid, 98%
Sigma-Aldrich
3-Ethyl-2,4-pentanedione, mixture of tautomers, 98%
Sigma-Aldrich
Oxalic acid, ReagentPlus®, ≥99%
Sigma-Aldrich
Salicylic acid, ReagentPlus®, ≥99%
Sigma-Aldrich
Sodium nitrate-14N, 99.95 atom % 14N
Sigma-Aldrich
Salicylic acid, ≥99%, FG
Sigma-Aldrich
Sodium nitrate, 99.995% trace metals basis
Sigma-Aldrich
Salicylic acid, puriss. p.a., ≥99.0% (T)
Sigma-Aldrich
Sodium hydroxide, BioUltra, for luminescence, ≥98.0% (T), pellets
Sigma-Aldrich
Sodium hydroxide solution, BioUltra, for molecular biology, 10 M in H2O
Sigma-Aldrich
Oxalic acid, purified grade, 99.999% trace metals basis
Sigma-Aldrich
Sodium nitrate, ACS reagent, ≥99.0%
Sigma-Aldrich
Sodium hydroxide, pellets, semiconductor grade, 99.99% trace metals basis
Sigma-Aldrich
Sodium hydroxide, ACS reagent, ≥97.0%, pellets
Sigma-Aldrich
Sodium hydroxide, reagent grade, 97%, flakes
Sigma-Aldrich
Sodium hydroxide, beads, 20-40 mesh, reagent grade, 97%
Sigma-Aldrich
Sodium hydroxide solution, 50% in H2O
Sigma-Aldrich
Sodium hydroxide, ultra dry, powder or crystals, 99.99% trace metals basis
Sigma-Aldrich
Sodium nitrate, anhydrous, free-flowing, Redi-Dri, ReagentPlus®, ≥99%
Sigma-Aldrich
Sodium hydroxide, reagent grade, 97%, powder
Sigma-Aldrich
Sodium hydroxide, reagent grade, ≥98%, pellets (anhydrous)