Ultrasound enhanced solid-phase extraction of ultra-trace arsenic on Fe₃O₄@AuNPs magnetic particles

Using ultrasound (US) to reduce the agglomeration of magnetic materials has attracted many researchers' attention in the field of magnetic solid phase extraction (MSPE). This paper showed that even the simple magnetic material (Fe₃O₄@AuNPs) can stimulate excellent arsenic (As) enrichment performance with the assistance of US. Compared with stirring dispersion, the extraction efficiencies of Fe₃O₄@AuNPs for 0.2 μg L^-1 As(III) and As(V) improved by a factor of about 6.2- and 5.7-times with ultrasonic agitation, respectively. Importantly, when the ultrasonic frequency and power are varied within a certain range, the extraction efficiency was increased by about 50% and 130%, respectively. This effect of ultrasonic frequency and power on the enrichment of arsenic by magnetic materials has never been reported. The number, dispersion uniformity and energy released by the bursting of cavitation bubbles under different conditions are considered to be the main reasons for the above phenomena. Additionally, the As(III) or As(V) can be converted into a gaseous product by in-situ slurry chemical hydride generation (SCHG) technology, and the material adsorbed by the material can be effectively removed, thereby ensuring that the complex is repeated at least 5 times or more. Under the optimized conditions, the whole enrichment process can be shortened from ~1 h to several minutes in the presence of US. At the same time, the linear calibration range was 0.01-3.0 μg L^-1 documenting that this US-assisted dispersive MSPE method coupled with a sensitive spectral detector (e.g. atomic fluorescence spectrometer, AFS) is suitable for analysis of inorganic As in natural water samples. The content of arsenic in five kinds of natural water samples ranged from 34 ng L^-1 to 2.3 μg L^-1.