Malays. J. Anal. Sci. Volume 29 Number 1 (2025): 1148

 

Research Article

 

Determination of natural organic ligands in tropical coastal water: In case of Fe(III) speciation

 

Khairul Nizam Mohamed*, Nur Amirah Zamri, Nur Jannati Ramjam, Ng Li Qing, and Syaza Syafiqah Muhamad Kamel

 

Department of Environment, Faculty of Forestry and Environment, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia

 

*Corresponding author: k_nizam@upm.edu.my

 

Received: 13 March 2024; Revised: 9 July 2024; Accepted: 12 November 2024; Published: 23 February 2025

 

Abstract

Natural Fe(III) organic ligand was determined in the Mersing coastal water. It was studied by determining the concentration of natural organic ligand ([LT]) and its constant stability (log KFeL) in seawater collected during pre-monsoon in August 2020, and post-monsoon in April 2021. Both seasons have different physical and chemical conditions due to the influence of the Northeast monsoon. The seawater samples from both sampling periods were analysed by using a competitive ligand equilibration-adsorptive cathodic stripping voltammetry (CLE-AdCSV) method. The [LT] in August 2020 ranged from 13.9±0.1 nM to 21.4±0.8 nM, which was higher compared to its concentration in April 2021. In April 2021, its concentration ranged from 9.1±0.1 nM to 19.3±1.2 nM. For the binding strength (log KFeL) of natural organic Fe(III) binding ligand in August 2020 and April 2021, it ranged between 11.1–11.8 and 10.6–11.9, respectively. This indicated the presence of a similar strong organic Fe (III) binding ligand class (L1) in our study area. Our present results suggested that the [LT] and log K showed no significant differences between August 2020 and April 2021 in Mersing coastal water. Despite the changes in in-situ parameters, they had no significant impact on the distribution of dissolved Fe(III) speciation (bioavailability), due to the presence of excess natural organic ligands in this coastal area. Hence, these strong organic ligands are important as they bind to the dissolved Fe(III) ions and create a Fe(III)-binding ligand complex that remains in the dissolved phase and make it bioavailable to organisms such as phytoplankton.

 

Keywords: organic ligand, Fe speciation, coastal water, binding strength, saturated state

 

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