Speciation analysis in chemistry

New fruit waste-derived activated carbons of high adsorption performance towards metal, metalloid, and polymer species in multicomponent systems

The main aim of the study was to develop new fruit waste-derived activated carbons of high adsorption performance towards metals, metalloids, and polymers by the use of carbon dioxide (CO2)-consuming, microwave-assisted activation. The authors compared morphology, surface chemistry, textural parameters, and elemental composition of precursors (chokeberry seeds, black currant seeds, orange peels), as well as biochars (BCs) and activated carbons (ACs) obtained from them. The adsorption mechanisms of metals (copper, cadmium), metalloids (arsenic, selenium), and macromolecular compounds (bacterial exopolysaccharide, ionic polyacrylamides) on the surface of selected materials were investigated in one- and two-component systems. Consequently, the capacities of BCs and ACs prepared through direct/indirect physical activation, using conventional/microwave heating were determined. It was noted that microwave heating favoured surface development and thus enhanced adsorbent ability to bind ions or macromolecules. Direct biomass activation led to higher microporosity compared to indirect (two-stage) one, whilst CO2-consuming activation increased aromaticity and hydrophobicity of the solids. In the two-component systems, polymers could favour metal/metalloid adsorption based on complexation phenomena. However, the most efficient and environmentally safe activated carbon turned out to be the one obtained from orange peels by microwave-assisted, direct activation at 800 °C in the CO2 atmosphere.

High-Throughput Preparation of Uncontaminated Graphene-Oxide Aqueous Dispersions with Antioxidant Properties by Semi-Automated Diffusion Dialysis

A semi-automated diffusion-dialysis purification procedure is proposed for the preparation of uncontaminated graphene oxide (GO) aqueous dispersions. The purification process is integrated with analytical-signal processing to control the purification degree online by several channels: oxidation-reduction potential, conductivity, and absorbance. This approach reduces the amounts of reagents for chemical treatment during dialysis. The total transition metal (Mn and Ti) content was reduced to a sub-ppb level (assessed by slurry nebulization in inductively coupled plasma optical atomic emission spectroscopy). Purified aqueous GO samples possess good stability for about a year with a zeta-potential of ca. -40 mV and a lateral size of ca. sub-µm. Purified GO samples showed increased antioxidant properties (up to five times compared to initial samples according to chemiluminometry by superoxide-radical (O₂^-) generated in situ from xanthine and xanthine oxidase with the lucigenin probe) and significantly decreased peroxidase-like activity (assessed by the H₂O₂-L-012 system).

Green and Simple Extraction of Arsenic Species from Rice Flour Using a Novel Ultrasound-Assisted Enzymatic Hydrolysis Method

It is well established that arsenic (As) has many toxic compounds, and in particular, inorganic As (iAs) has been classified as a type-1 carcinogen. The measuring of As species in rice flour is of great importance since rice is a staple of the diet in many countries and a major contributor to As intake in the Asian diet. In this study, several solvents and techniques for the extraction of As species from rice flour samples prior to their analysis by HPLC-ICP-MS were investigated. The extraction methods were examined for their efficiency in extracting various arsenicals from a rice flour certified reference material, NMIJ-7532a, produced by the National Metrology Institute of Japan. Results show that ultrasound-assisted extraction at 60 °C for 1 h and then heating at 100 °C for 2.5 h in the oven using a thermostable α-amylase aqueous solution was highly effective in liberating the arsenic species. The recoveries of iAs and dimethylarsinic acid (DMA) in NMIJ-7532a were 99.7% ± 1.6% (n = 3) and 98.1% ± 2.3% (n = 3), respectively, in comparison with the certificated values. Thus, the proposed extraction method is a green procedure that does not use any acidic, basic, or organic solvents. Moreover, this extraction method could effectively maintain the integrity of the native arsenic species of As(III), As(V), monomethylarsonate (MMA), DMA, arsenobetaine (AsB) and arsenocholine (AsC). Under the optimum extraction, chromatography and ICP-MS conditions, the limits of detection (LOD) obtained were 0.47 ng g−1, 1.67 ng g−1 and 0.80 ng g−1 for As(III), As(V) and DMA, respectively, while the limits of quantification (LOQ) achieved were 1.51 ng g−1, 5.34 ng g−1 and 2.57 ng g−1 for As(III), As(V) and DMA, respectively. Subsequently, the proposed method was successfully applied to As speciation analysis for several rice flour samples collected from contaminated areas in China.