Fabrication of a porous hydrangea-like Fe3O4@MnO2 composite for ultra-trace arsenic preconcentration and determination.

Fe3O4@MnO2 magnetic composite microsphere with hierarchical shells structure has been synthesized through a facile two-step hydrothermal reaction for ultra-trace arsenic enrichment. Scanning electron microscopy and transmission electron microscopy images clearly indicated that the as-synthesized material is a porous hydrangea-like morphology, as well as the size of the composite microspheres and the widths of pore are related to the reaction conditions. The N2 adsorption-desorption isotherms demonstrated that the specific surface areas and pore volume of Fe3O4@MnO2 with 8 h hydrothermal synthesis are 121.9260 m2 g-1 and 0.21 cm3 g-1, respectively. The enrichment performance of composites depends on their compositions, and the recovery of As(III) on Fe3O4@MnO2 with Mn/Fe ratio 1:2 was 1-2.3 times of that on other ratios. In comparison with As(V), experimental data indicated that the prepared composites have faster adsorption rate for As(III). In addition, slurry sampling chemical hydride generation technology can effectively remove and reduce the adsorbed As(III) or As(V) to the gaseous product, thus ensuring that the composite is at least repeated over 5 times. Under the optimized conditions, the detection limit of the proposed method was 2.9 ng L-1 and relative standard deviation of 4.8% for 0.1 µg L-1 As(III) was obtained. The linear calibration range was 0.01-1.5 µg L-1. The accuracy of the method was verified through analysis of the certificated reference materials. The proposed method has been applied to the determination of inorganic As in natural water samples.

Dual-frequency ultrasound assisted-enzyme digestion coupled with atomic fluorescence spectrometry as a green and efficient tool for cadmium detection in rice flour samples.

A sample treatment technique based on a duel frequency ultrasonic device for enzymatic digestion of rice is reported. The ultrasonic device combines a high intensity ultrasonic probe and the temperature control function of ultrasonic water bath, which can effectively extract cadmium from rice within only 160 s under the optimized conditions. Compared with the traditional ultrasonic assisted enzymatic digestion, the new method not only shortens the time significantly (e.g., from the 90 min of ultrasonic water bath to the present few minutes), but also increases the extraction efficiency of cadmium (such as ~ 75% from ultrasonic probe to app. 100%). Through the optimization of ultrasonic mode, ultrasonic frequency, power and the type of enzyme, we found that enzyme played a dominant role in ultrasound assisted enzymatic digestion. Compared with a-amylase and pepsin, trypsin is more suitable for the extraction of cadmium from rice. Furthermore, ultrasound energy is beneficial to enzymatic hydrolysis of bimolecular, and this promotion is related to the frequency of ultrasound. The reliability of this method was evaluated by analyzing the content of cadmium in the certified reference materials (CRMs, GBW10045, GBW08510, GBW08511 and GBW08512) based on atomic fluorescence spectrometry combined with a modified chemical vapor generation. The proposed method has been applied satisfactorily in the determination of Cd in several rice samples.