In:
Applied Spectroscopy, SAGE Publications, Vol. 69, No. 11 ( 2015-11), p. 1293-1302
Abstract:
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 (logK 1 and logK 2 ) of the two components all increased with increasing pH. In buffered solutions, the new quenching model reported logK 1 = 7.11, 7.89, 8.04 for C1 and logK 2 = 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, logK 1 and logK 2 decreased but were still high ( 〉 7) at pH 8.0 (logK 1 = 7.54, logK 2 = 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.
Type of Medium:
Online Resource
ISSN:
0003-7028
,
1943-3530
Language:
English
Publisher:
SAGE Publications
Publication Date:
2015
detail.hit.zdb_id:
1474251-2
SSG:
11
Permalink
