UV reduction with ultrasound-assisted gas–liquid separation for the determination of mercury in biotissues by atomic absorption spectrometry

Abstract

The synergic effect of ultraviolet (UV) and ultrasound (US) radiation when used in combination has been exploited for efficient generation of Hg vapour in atomic absorption spectrometry. For this purpose, a batch reactor is designed and coupled to an atomic absorption spectrometer arranged with a quartz cell in the optical path. UV irradiation achieved a fast reduction of ionic Hg to elemental Hg in the presence of formic acid used as a precursor of reducing species, whereas high intensity ultrasound irradiation allowed a fast mass transfer from the liquid sample to the gas phase of the reactor. UV reduction times of 10 s and 30 s were needed for Hg(II) and CH₃Hg⁺, respectively. A 5 s ultrasound irradiation time was enough to yield an atomic absorption signal integrable within 20 s. Formic acid was useful not only to assist the photoreduction but also to solubilize the biological tissues. The method was applied to the determination of total Hg in four certified reference materials corresponding to marine biological tissues following fast ultrasound-assisted solubilization with formic acid. LODs of Hg in the biological tissues ranged from 0.025 to 0.06 μg g⁻¹. Within-batch precision was around 4%, whilst between-batch precision was in the range 6–11%.