PEER-REVIEWED ARTICLE bioresources.com Ajab et al. (2020). “Trace aqueous Pb(II) detection,” BioResources 15(3), 6273-6281. 6273 Optimization of Oil Palm-based Cellulose and Hydroxyapatite-Carbon Composite Electrode for Trace Pb(II) Ions Detection in Aqueous System Huma Ajab, a,b Asim Yaqub, c Muhammad Shahid Nazir, d Mohd Zul Helmi Rozaini, e and Mohd Azmuddin Abdullah e, * An electroanalytical technique was devised using oil palm-based cellulose and hydroxyapatite as modifiers to carbon electrodes for Pb(II) ions detection in an aqueous system. The cyclic voltammetry scan suggested increased active binding sites and faster electron transfer with quasi- reversible redox peaks with a larger anodic current peak and smaller oxidation potential values. The optimal conditions were attained using 10% modifier at pH 2 in 0.1 M HCl, −1.2 V deposition potential, 270 s deposition time, 25 Hz frequency, 0.020 V amplitude, rotation speed of 700 rpm, and the step potential of 0.005 V. The square wave anodic stripping voltammetry established at optimum level exhibited excellent selectivity and stability from 10 ppb to 100 ppb for Pb(II) ions detection. Sharp anodic peaks were observed at -0.48 V for Pb(II) ions with the detection limit of 0.095 ± 0.32 ppb and limit of quantitation of 0.32 ± 0.32 ppb. Keywords: Metal ion; Carbon composite electrode; Cellulose; Hydroxyapatite; Square-wave voltammetry Contact information: a: Department of Chemical Engineering, Universiti Teknologi PETRONAS, 32610 Seri Iskandar, Perak, Malaysia; b: Department of Chemistry, COMSATS University Islamabad, Abbottabad, 22060, Pakistan; c: Department of Environmental Sciences, COMSATS University Islamabad, Abbottabad, 22060, Pakistan; d: Department of Chemistry, COMSATS University Islamabad, Lahore Campus, 54000, Punjab, Pakistan; e: Institute of Marine Biotechnology, Universiti Malaysia Terengganu, 21030 Kuala Nerus, Terengganu, Malaysia; *Corresponding author: joule1602@gmail.com INTRODUCTION Heavy metal contamination is a type of hazardous environmental pollution that has major impacts on health, soil, and water ecosystems, with long-term economic and financial repercussions. The amount of heavy metal sludge constitutes approximately 4.9% of 1.7 million metric tons of total sewage wastes generated in Malaysia (Fen and Mahmood Mat Yunus 2013). Among these, lead (Pb) exhibits strong chemical toxicity on nervous, gastrointestinal, immune, and reproductive systems and can be detrimental even at low concentrations. As the water system contaminated with the toxic metals may finally enter the marine and human food chain, the detection must be sensitive and selective with the possibility of extending it for in situ and on site applications (Fen and Mahmood Mat Yunus 2013; Ajab et al. 2019; Khan et al. 2019). Conventional techniques using complicated instrumentations such as atomic absorption spectrometry (AAS) or inductively coupled plasma mass spectrometry (ICP-MS) are expensive and not suitable for on-site analysis. These also require well-controlled experimental conditions, time-consuming preparation steps, and operated by specialized personnel (El Mhammedi et al. 2010). Reliable techniques for environmental sample analyses are important for knowledge-based and well-informed decision making to safeguard the health of public, accelerate developments in technology, and for the improvement of environmental quality.