Simple Voltammetric Determination of Iron in Ethanol and Biodiesel Using a Bismuth Film Coated Glassy Carbon Electrode

Abstract

Square-wave adsorptive stripping voltammetry (SWAdSV) was used to determine iron in ethanol and biodiesel using a bismuth-film electrode (BiFE) prepared onto the surface of a glassy carbon electrode (GCE) by electrochemical deposition to promote the reduction of Fe (III) previously complexed with 1-(2-pyridylazo)-2-naphthol (PAN) directly in the electrochemical cell. The supporting electrolyte was composed by mixture of acetate buffer (0.1 mol L⁻¹, pH 4.5) and ethanol (40/60% v/v) into which 500 µL of a 0.1 mmol L⁻¹ stock solution of PAN was added as complexing agent. The Fe (III)-PAN complex presented a well-defined current peak at −0.7 V. For biodiesel, a treatment with tetramethylammonium hydroxide (TMAH) was proposed as an efficient mean to minimized matrix interferences. A limit of detection of 6.0 × 10⁻⁸ mol L⁻¹ (0.06 µmol L⁻¹) and limit of quantification of 2.0 × 10⁻⁷ mol L⁻¹ (0.2 µmol L⁻¹) were obtained for Fe(III). Under the optimized conditions, there were no significant interferences from Cu(II), Al(III), Mn(II), Cr(III), Cd(II), Zn(II) and Ni(II) and Pb(II) while Ni(II) interfered significantly. The analytical curves produced linear responses with equations I (µA) = (-1.315 × 10⁻⁷ ± 5.158 × 10⁻⁸) + (-0.238 ± 0.01) [Fe (III)] (µmol L⁻¹), R² = 0.992 and I (µA) = (-6.836 × 10⁻⁷ ± 1.124 × 10⁻⁸) + (-0.408 ± 0.013) [Fe (III)] (µmol L⁻¹), R²=0.998 for pure ethanol and biodiesel, respectively. The method produced satisfactory results in quantifying original quantities of Fe(III) in fuel ethanol (5.65 ± 0.71 µmol L⁻¹) and biodiesel (1.28 ± 0.25 µmol L⁻¹) at a 95% confidence limit (n = 3).

Keywords:

• Fe (III)-1-(2-piridylazo)-2-naphthol
• tetramethylammonium hydroxide
• bismuth-film electrode
• square-wave adsorptive stripping voltammetry
• ethanol
• biodiesel

Acknowledgements

The authors are grateful to CAPES-PROCAD AM (Edital PROCAD AMAZÔNIA 2018 – Line 2; Number SCBA: 88887.200615/2018-00), CNPq (PQ 2017, Proc. 310664/2017-9); FAPEMA (Proc. Edital UNIVERSAL-01136/17) and ANP (Research Project PMQC/QUALIPETRO, N^o 1.028/2021; CONSEPE-UFMA N^⍛ 2.460/22) for the financial support and fellowships received.

Authors’ contributions

Almeida J.M.S: Investigation, methodology, formal analysis and writing.

Ribeiro A.B.P: Investigation, methodology and formal analysis.

Toloza C.A.T: Investigation, methodology, writing and editing.

Santos J.R.N: Investigation, methodology and formal analysis.

Alves I.C.B: Investigation, methodology and formal analysis.

de Azevedo L.C.M: Investigation, methodology and writing.

Aucélio R.Q: methodology, writing and editing.

Marques A.L.B: Funding, methodology, writing and editing.

Competing interests

The authors declare no conflicts of interest.

Consent for publication

The article is original which has neither been published previously nor submitted to more than one journal for simultaneous consideration.

Ethical approval and consent to participate

The article does not contain any studies with human participants or animal subjects and all authors are entitled to authorship and have approved the final version of the submitted manuscript.

Additional information

Funding

This study was supported by Coordenação de Aperfeiçoamento de Pessoal de Nível Superior [PROCAD-AM/SCBA 450 88887.200615/2018-00], Conselho Nacional de Desenvolvimento Científico e Tecnológico [PQ 2017, Proc. 310664/2017-9], and Agência Nacional do Petróleo, Gás Natural e Biocombustíveis - ANP [Research Project PMQC/QUALIPETRO, No 1.028/2021].