Nano-bismuth sulfide based dispersive micro-solid phase extraction combined with energy dispersive X-ray fluorescence spectrometry for determination of mercury ions in waters

Abstract

A selective method for the determination of mercury ions in different types of water samples by energy dispersive X-ray fluorescence spectrometry (EDXRF) was developed. Quantification of Hg(II) by EDXRF was preceded by ultra-sound assisted dispersive micro-solid phase extraction (USA-DMSPE) on nano-bismuth sulfide (nano-Bi₂S₃) as a solid sorbent. At pH 1 nano-Bi₂S₃ selectively adsorbs Hg(II) ions from aqueous samples with an adsorption capacity of 499.1 mg g⁻¹. The experimental data fitted well with the Langmuir isotherm model, which confirms the chemical character of the adsorption process. Under optimized preconcentration conditions, i.e. a sample pH of 1, adsorbent mass of 1 mg, sample volume of 50 mL and sonication time of 15 min, the linear response between fluorescence radiation intensity and the metal concentration was obtained within 1–200 ng mL⁻¹ range with a correlation coefficient of 0.9988. The method allows the detection of mercury ions at a concentration of only 0.06 ng mL⁻¹. The determination of Hg(II) ions after the nano-Bi₂S₃ based USA-DMSPE-EDXRF procedure is possible even in the presence of a high concentration of anions and cations typically coexisting in surface waters. The described method was applied to the determination of Hg(II) ions in mineral, spring, river, and artificial sea waters. The correctness of the procedure was confirmed by analysis of the certified reference material (Seawater QC3163).