Optimisation of Electrokinetic Extraction System: Colourimetric Determination of Copper (II) in Sand Using Polymer Inclusion Membrane

ABSTRACT

Electrokinetic extraction (EKE), coupled with polymer inclusion membranes (PIMs) for colourimetric detection, offers a promising approach for extracting metal ions from solid matrices, such as sand, without sample pretreatment. Our EKE system consists of a formic acid gel positioned at the cathode side to neutralise hydroxide ions generated by electrolysis during the EKE of Cu(II), whereas the anode side contains the sample compartment, prepared from a syringe tube into which the sample is placed. The PIM is sandwiched between these compartments to accumulate Cu(II) via EKE through the sand and into the PIM within which it complexes with a colour‐forming reagent, 1‐(2‐pyridylazo)‐2‐naphthol (PAN), enabling quantification via colourimetric analysis. The system has been optimised to expand the quantification range of Cu(II), thus allowing greater applicability to a wider range of samples with different levels of heavy metals. Increasing the column diameter extended the upper limit of the quantification range from 7.5 mg kg ⁻¹ (4.5 mm column diameter) to 30.0 mg kg ⁻¹ (13.5 mm column diameter). Concurrently, optimisation of the PIM composition, containing 43.3 wt% cellulose triacetate (CTA)–56.0 wt% di‐(2‐ethylhexyl) phosphoric acid (D2EHPA)–0.8 wt% PAN, enhanced the overall recovery of Cu(II) from 64% ± 7% to 90% ± 4%. Overall, the optimised system has achieved a quantification range of 2.8–30.0 mg kg ⁻¹ of Cu(II), with an LOD of 0.9 and LOQ of 2.8 mg kg ⁻¹ of Cu(II).