Highly selective and sensitive determination of mercury ions by total-reflection X-ray fluorescence spectrometry

Abstract

In this work, a fast and low-cost method for the highly selective determination of ultratrace Hg(II) ions by total-reflection X-ray fluorescence spectrometry (TXRF) is presented. The procedure is based on dispersive micro-solid phase extraction (DMSPE) using thiosemicarbazide-functionalized carbon nanotubes (CNT-TSC). The experiment shows that Hg(II) ions are affectively adsorbed on CNT-TSC at pH 2 within 10 min using an extremely low adsorbent dosage of 1 μg mL⁻¹. Moreover, CNT-TSC is characterized by excellent selectivity toward Hg(II) ions, which can be quantitatively adsorbed from the solution of very high ionic strength (5 mol L⁻¹) and in the presence of the coexisting ions at extremely high concentrations (100 000-fold excess). After the preconcentration/separation step, the suspension of CNT-TSC with adsorbed Hg(II) ions is pipetted onto a quartz reflector and dried. This article shows that the procedure allows overcoming the problems with the volatilization losses of mercury and eliminating the matrix effects in high salinity water. The quantitative DMSPE/TXRF analysis can be performed using the classical calibration curve and simplified approach using only an internal standard. The method is characterized by a very low detection limit of 2.6 pg mL⁻¹ and uses minimal amounts of chemical reagents and a low-power TXRF instrument. The method was applied to analyze water samples, including seawater, and biological samples: lobster hepatopancreas, herring, cormorant, and cod tissues. The excellent selectivity and high adsorption capacity of CNT-TSC toward Hg(II) ions (188 mg g⁻¹) also open the path for the effective removal of Hg(II) ions from aqueous solutions.