Determination of complexing capacity of fulvic acid for copper(II) and cadmium(II) by dialysis titration

Abstract

The complexing capacity of a solution is a measure of the metal Ion blndlng ability of the dissolved ligands. The purpose of this study Is to evaluate dlalysls titration as a method of determlnlng the complexlng capacity of soil-derlved fulvic acld (SFA). In a prellmlnary experiment, we titrated 6.25 pM ethylenediaminetetraacetlc acld (EDTA) at pH 6 with Cu2+ and Cd2+ and obtained complexing capacity values within 2.4% of theoretlcal. Next, 15.5 pM SFA was titrated with Cu2+ or Cd2+ at pH 5, 6, and 7 during 30-day dialysis experiments. The SFA complexlng capacity values are greater for Cu2+ than for Cd2+ at the same pH and generally Increase for elther Cu2+ or Cd2+ as pH increases. We estimate that a maximum of 10% of the complexing capacity permeates the dialysis membrane. A statistical comparison of dlalysls and Cu2+ ISE results shows no dlfference in the abllity of the two techniques to measure complexing capacity.The complexing capacity of isolated humic matter (fulvic and humic acids) and humic matter dissolved in natural waters is its ability to complex free (hydrated) metal ions. The analytical difficulty inherent with complexing capacity measurements is to distinguish the free metal species from the complexed species, including labile complexed metal ions, and at the same time have minimal effect on the chemical equilibrium under study. In the past, researchers have employed biological and chemical techniques to make these exacting measurements. Biological methods often shift equilibria less than chemical methods but offer a smaller range of metal ions that can be studied (1-3). Chemical methods offer precision, convenience, sensitivity, and a greater number of metal ions that can be studied.It is convenient to place chemical methods in three categories: miscellaneous, electrochemical, and membrane separation or gel titration chromatography (GFC). The miscellaneous category includes a copper(I1) solubilization method (4, 51, a cobalt(II1) complexation method (6, 7), and chromatographic methods using MnOz (49) or Chelex-100 resinElectrochemical methods are especially popular. In particular, metal ion selective electrode (ISE) potentiometric titrations are commonly employed to determine complexing capacities (13)(14)(15)(16)(17)(18)(19). Many research groups use voltammetric titrations of measure metal ion complexing capacities (20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30), although this application of voltammetry is controversial because of potential interferences with the working electrode A group of analytical methods to determine metal ion binding capacities by separation use GFC (38-40), ultrafiltration (41), or dialysis (42-46) to segregate free metal ions from metal complexes during a titration. Then the researcher can determine concentrations of both metal species by various (31 -37).'Present address: Celanese Research Co., 86 Morris Av., Summit, NJ 07901. analytical techniques to meet detection limits and specify requirements for many metal ions, An advantage offered by dialysis is the ability t...

Copper binding by the root cell walls of Italian ryegrass and red clover

“…Moreover, several attempts have been made to determine the complexing capacity of humic substances (Truitt and Weber 1981;Yamada et al 1987). Based on this concept, we attempted to evaluate the maximum Cu-binding capacity (MCBC) of the root cell wall fraction, according to the method described by Nishimura (1979).…”

A Surrogate Approach to Studying the Chemical Reactivity of Burrow Mucous Linings in Marine Sediments

“…A non-electrostatic model was chosen as only one ionic strength was explored (0.01 M), and previous studies have demonstrated that electrostatic surface field effects on protonation are minimal for bacterial surfaces (Borrok et al, 2004) and humic and fulvic acids (Truitt and Weber, 1981). Titration data were modeled using leastsquares optimization as implemented in FITEQL 4.0 (Herbelin and Westall, 1999).…”

“…As adsorption of free Cd by mucin-reactive sites occurs, Cd 2+ in solution crosses the semipermeable membrane until equilibrium is reached. To achieve Cd 2+ equilibrium between the diffusate and the retentate solutions, the experiments were placed in an incubator at 25 uC while undergoing constant agitation (40 rpm) for a period of 24 hours (Truitt and Weber, 1981).…”

Natural organic matter and colloid-facilitated arsenic transport and transformation in porous soil media

“…Solid KC1 was added to the outside solutions until the ionic strength as measured by a conductivity meter (Model 441, Corning Inc. New York) matched that o f the inside solution. The volume ratio of outside/inside solution was set at 26: 1 (Truitt and Weber, 1981). During the dialysis process, the closed containers were continuously stirred with a magnetic stirrer at 25°C for five days.…”

“…Dissociation could occur during size exclusion chromatographic separation (Amy et al, 1987;Logan and Wagenseller, 2000). (Buschmann and Sigg, 2004;Haitzer et al, 2002;Jansen et al, 2003;Truitt and Weber, 1981). Very few studies, however, have dealt with metalloid As (Lin et al, 2004).…”