Rapid determination of formic and acetic acids in biomass hydrolysate by headspace gas chromatography

Determination of acetic acid in enzymes based on the cataluminescence activity of graphene oxide-supported carbon nanotubes coated with NiMn layered double hydroxides

A cataluminescence (CTL) method has been developed for the rapid determination of acetic acid in enzyme products. The NiMn LDH/CNT/GO was synthesized based on the nanohybridization of NiMn layered double hydroxide (NiMn LDH), carbon nanotubes (CNTs), and graphene oxide (GO). The composite has excellent CTL activity against acetic acid. It could be ascribed to the larger specific surface area and more exposure to active sites. NiMn LDH/CNT/GO is used as a catalyst in the CTL method based on its special structure and advantages. There is a linear relationship between CTL response and the acetic acid concentration in the range 0.31-12.00 mg·L^-1 with the detection limit of 0.10 mg·L^-1. The developed method is rapid and takes only about 13 s. The method is applied to the determination of acetic acid in enzyme samples with little sample preparation. The result of the CTL method shows good agreement with that of the gas chromatography method. The proposed CTL method possesses promising potential in the quality monitoring of enzymes.

Photocatalytic hydrogen evolution from glycerol-water mixture under visible light over zinc indium sulfide (ZnIn2S4) nanosheets grown on bismuth oxychloride (BiOCl) microplates

ZnIn₂S₄ (ZIS) is one of the widely studied photocatalyst for photocatalytic hydrogen evolution applications due to its prominent visible light response and strong reduction ability. However, its photocatalytic glycerol reforming performance for hydrogen evolution has never been reported. Herein, the visible light driven BiOCl@ZnIn₂S₄ (BiOCl@ZIS) composite was synthesized by growth of ZIS nanosheets on a template-like hydrothermally pre-prepared wide-band-gap BiOCl microplates using simple oil-bath method to be used for the first time for photocatalytic glycerol reforming for photocatalytic hydrogen evolution (PHE) under visible light irradiation (λ > 420 nm). The optimum amount of BiOCl microplates in the composite was found 4 wt% (4% BiOCl@ZIS) in the presence of in-situ 1 wt% Pt deposition. Then, the in-situ Pt photodeposition optimization studies over 4% BiOCl@ZIS composite showed the highest PHE rate of 674 μmol g^-1h^-1 with the ultra-low platinum amount (0.0625 wt%). The possible mechanisms behind this improvement can be ascribed to the formation of Bi₂S₃ low-band-gap semiconductor during BiOCl@ZIS composite synthesis resulting in Z-scheme charge transfer mechanism between ZIS and Bi₂S₃ upon visible light irradiation. This work expresses not only the photocatalytic glycerol reforming over ZIS photocatalyst but also a solid proof of the contribution of wide-band-gap BiOCl photocatalysts to enhancement of ZIS PHE performance under visible light.

Influence and Mechanism of Polar Solvents on the Retention Time of Short-Chain Fatty Acids in Gas Chromatography

Short-chain fatty acids (SCFAs), produced by microbes when dietary fiber ferments in the colon, are one of the most studied microbial products despite their volatility and complex matrices, which make analysis challenging. In the current study, we sought to address research gaps by exploring the commonalities and differences between the retention time changes for SCFAs in polar solvents. In one such solvent, dimethyl sulfoxide (DMSO), the retention time of the SCFA acetic acid shows a linear positive correlation with the equal volume increase in the DMSO solvent. We used gas chromatography–mass spectrometry to analyze the retention times of mixed solutions of formic acid, acetic acid, butyric acid, valeric acid, and toluene in the solvents DMSO and water and found that only the retention times of formic acid and acetic acid changed. We further compared the effect of three solvents with similar polarities, DMSO, N-methylpyrrolidone (NMP), and dimethylformamide (DMF), on the retention time of acetic acid and found that it increased in the DMSO–water solution more than in the NMP–water solution and remained unchanged in the DMF–water solution. This finding is consistent with quantum chemical calculations showing that the strength of the hydrogen bond between DMSO and acetic acid is greater than between NMP and acetic acid. Taken together, the chromatographic results and quantum chemical calculations indicate that, in all three solvents, the portion of the molecule with the smallest negative electrostatic potential (red) has high electron density and can easily donate electrons, forming a hydrogen bond with acetic acid. However, the portion with the largest positive electrostatic potential (blue) forms a bond with polyethylene glycol, a column stationary solution with a strong dipole moment, and is adsorbed on the stationary solution in the direction of the dipole moment. Therefore, the retention times of formic acid and acetic acid change under the combined influence of a series of complex intermolecular forces. In the chromatographic column, the outflow rate of DMF is higher than that of acetic acid, and the force of the hydrogen bond between DMF and acetic acid cannot overcome the outflow resistance of acetic acid, so the retention time of the acetic acid in the DMF–water solution does not change. The retention times of butyric acid and valeric acid are unchanged in aprotic polar solvents for the same reason.

Acidic and alkaline gas sensitive and self-healing chitosan aerogel based on electrostatic interaction

Gas pollution is a serious problem. More attention has been paid to the detection and monitoring of toxic and harmful gases, and it is urgently needed for a sensor that could simultaneously identify and distinguish between acid and base gases. Based on the electrostatic interaction resulting from amidogen of chitosan (CS) and carboxylic groups of itaconic acid (IA), we successfully prepared a series of biomass aerogels (CS-IA aerogels) that could respond to acidic and alkaline gases with different concentrations. The acidic and alkaline gases could be easily detected and distinguished by changing the content of IA in CS-IA aerogels. Moreover, the electrostatic interactions could also endowed CS-IA aerogels with self-healing ability in the breaks at room temperature. After self-healing, CS-IA aerogels still sensitively answered to acidic and alkaline gases. CS-IA aerogels with sensitivity to acid-base gas and self-healing performance has been suggested to be promising candidates as application of multi-functional aerogels.

An efficient headspace gas chromatographic technique for determining humic acid content in fertilizer

A fast, convenient and commercially available approach for analyzing humic acid content in fertilizer using headspace gas chromatography (HS-GC) is presented in this paper. Humic acid is converted into carbon dioxide based on the oxidation of humic acid in strong acidic medium and can be measured via automatic HS-GC. Conditions for the alkaline extraction and the humic acid oxidation process are also optimized. The new technique proved to be precise (RSD ≤ 3.59%) and accurate (relative errors≤9.46% as compared with the spectrophotometric approach). The newly established technique presents a practical tool to routinely analyze humic acid content in fertilizer during the fertilizer production.