ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Quantitative analysis of organosulphur compounds in crude oil samples using magnetic solid phase extraction based on Au-Fe₃O₄ adsorbent and gas chromatography with time-of-flight mass spectrometry

Samuel S. Mgiba, V. Mhuka, N. C. Hintsho-Mbita, and Nomvano Mketo

Department of Chemistry, College of Science, Engineering and Technology (CSET), University of South Africa, Florida Science Campus, Johannesburg, South Africa

E-mail: nomvano.mketo@gmail.com

Received: 23 September 2023  Accepted: 13 April 2024

Abstract:

This study focused on the development of a magnetic solid phase extraction (m-SPE) method using Au-Fe₃O₄ as an adsorbent followed by GC-ToFMS analysis for the determination of organosulphur compounds (OSCs) in fuel samples. The m-SPE using Au-Fe₃O₄ NPs was preferred because of the low toxicity of the adsorbent¹, high separation efficiency using external magnet² and greater extraction selectivity between sulphur and Au atom³. The Au-Fe₃O₄ NPs were characterized using XRD, UV–Vis, TEM, SEM and FTIR. This method was optimized using multivariate analysis based on a two-level full factorial and central composite designs. The conditions which produced optimum efficiency were found to be 150 mg mass of sorbent, 100 µL eluent volume, 50 min extraction time and 6,5 pH of the sample. These optimum conditions showed a relatively low limit of detection in the range of 0.02–0.199nµg/g and limit of quantification of 0.08–0.602 µg/g. Furthermore, a relative standard deviation of triplicates analysis was between 0.8 and 2.3% with good linearity of 0.9816–0.9961. The percentage recovery for thiophene, 3-methylthiophene, benzothiophene and dibenzothiophene ranged from 76 to 95% for the spiked samples. The optimized m-SPE method was then applied in real fuel oil samples. The concentration of thiophene, 3-methylthiophene, benzothiophene and dibenzothiophene in crude oil, gasoline, diesel and kerosene ranged from 0.43–1.94 µg/g, 0.78–1.63 µg/g, 0.95–4.31 µg/g to 1.55–2.09 µg/g, respectively. The m-SPE, followed by GC-ToFMS method, proved to be efficient, inexpensive and an alternative method for OSCs analysis in fuel oils.

Keywords: Magnetic solid phase extraction; Au-Fe3O4 adsorbent; Organosulphur compounds; GC-ToFMS; Gasoline; Diesel; Kerosene

Full paper is available at www.springerlink.com.

DOI: 10.1007/s11696-024-03465-8

Chemical Papers 78 (9) 5275–5288 (2024)