In this work, high-performance liquid chromatography in combination with inductively coupled plasma dynamic reaction cell quadrupole mass spectrometry was introduced and optimized for speciation analysis of five major arsenic species including arsenobetain (AsB), arsenite (As(III)), monomethylarsonic (MMA), dimethylarsenonic acid (DMA), and arsenate (As(V)) in rice samples. Five arsenic compounds were separated on a Hamilton PRP X100 strong anion-exchange column employed with the mobile phase that is compatible with mass spectrometry, containing ammonium carbonate, methanol, and disodium ethylenediaminetetraacetic acid. Arsenic compounds were detected online by inductively coupled plasma dynamic reaction cell quadrupole mass spectrometry utilizing oxygen as the reaction gas at a flow rate of 0.7 mL·min−1. Five selected arsenic species were baseline separated at the optimum experimental conditions. The excellent LOD and LOQ values of the developed method were achieved in the range of 0.5 to 2.9 μg·kg−1 and 1.7 to 9.6 μg·kg−1 for all species of arsenic, respectively. The ionization effect in plasma during chromatographic gradient elution was systematically investigated by using postcolumn injector. Arsenic compounds in rice samples were extracted by diluted nitric acid at elevated temperature. The extraction efficiency and the interconversion of target compounds during sample preparation were also assessed. The full validation of the developed method was performed by using certified reference material, BRC 211, from European Institute of Reference and Standard for speciation analysis. The recovery of all selected arsenic species was in the range of 70 to 135.5%. The validated method was also applied to analyze rice samples collected from some contaminated rice fields. The results showed that As(III), DMA, and As(V) were found in all rice samples. Average concentration (range) of inorganic arsenic and DMA in all rice samples were 130.3 (65.5–228.1) and 32 (8.2–133.01) μg·kg−1, respectively. However, total concentration of inorganic arsenic in most of investigated rice samples was below the maximum residual level according to US-FDA and European Union standards.
Particulate matter (PM) is a major environmental concern in Vietnam as well as in the world. Samples of PM2.5, PM10, and total suspended particle (TSP) were collected on the rooftop of a five-floor building inside Hanoi University of Science and Technology, Hanoi, from January to May 2015. The levels PM2,5, PM10, and the metal elements of TSP were determined. PM2,5 and PM10 had average concentrations of 73 ± 37 and 138 ± 67 μg\m3, respectively. The concentration of PM2,5 and PM10 in all samples were higher than the recommended level in the World Health Organization (WHO) guideline (2005) for 24h and annual concentrations of 25 and 50 μg\m3, respectively. Nineteen elements detected in TSP samples included the higher concentration group in order: Ca > Fe > Na > Al > Mg > K > Zn and in the lower concentration group: Pb > Mn > Ti > Sr > V > Cr > Cd. The potential sources revealed from element components were discussed.
CuMnOx spinel catalyst, prepared by the sol-gel method, and characterized by modern techniques such as XRD, BET, H2-TPR, EPR, were used to oxide toluene in the temperature range from 150oC to 400oC . Among, the investigated catalysts as MnO2, CuO, and CuMnOx, the CuMnOx showed the highest catalytic activity. It converted 100% toluene to CO2 at 250oC in excessed oxygen conditions. The higher catalytic performance of CuMnOx than MnO2, CuO because of its higher specific surface area and its lower reduction temperature. The results also implied that the interaction between Cu and Mn could improve the reduction capacity of CuMnOx catalyst. In summary, the CuMnOx catalyst is a promising catalyst for toluene treatment.
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