Reduced graphene oxide-polyaniline nanocomposite as an efficient adsorbent for solid phase extraction of Co²⁺ followed by electrothermal atomic absorption spectrometry

An efficient adsorbent, reduced graphene oxide-polyaniline (rGO-PANI) nanocomposite was used for solid phase extraction and pre-concentration of ultra-trace levels of Co²⁺ in different real samples. Graphene oxide (GO) was synthesised from graphite by Hummer method and after reduction by NaBH₄, it was modified with poly-aniline to produce rGO-PANI. Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and electron–dispersive X-ray spectroscopy (EDS) were used for characterisation of the synthesised rGO-PANI nanocomposite. The main parameters affecting the extraction efficiency such as pH, amounts of adsorbent, extraction and desorption times were optimised by response surface methodology based on central composite design (RSM-CCD). According to the results, pH 8, 5.8 mg rGO-PANI, 15 min extraction time and 8 min desorption time were selected as the optimum values.

Under the optimum conditions, the calibration curve was linear in the range of 0.05–0.6 µg L⁻¹ for Co²⁺. The relative standard deviation (%RSD) for seven replicate analysis of 0.2 µg L⁻¹ Co²⁺ was 3.2% and the limit of detection (LOD) was 0.017 µg L⁻¹ Co²⁺ (n = 7). The certified reference material, CRM-TMDW, was successfully used to validate the accuracy of the proposed method and finally, this technique was applied for determination of ultra-trace levels of Co²⁺ in different water and food samples.