Qiuhua Wu

Metal–Organic Framework Derived Magnetic Nanoporous Carbon: Novel Adsorbent for Magnetic Solid-Phase Extraction

The fabrication of a magnetic nanoporous carbon (MNPC) via one-step direct carbonization of Co-based metal-organic framework has been achieved without using any additional carbon precursors. The morphology, structure, and magnetic behavior of the as-prepared Co-MNPC were characterized by using the techniques of scanning electron microscopy, transmission electron microscopy, powder X-ray diffraction, Raman spectroscopy, N2 adsorption, and vibrating sample magnetometer. The Co-MNPC has a high specific surface area, large pore volume, and super paramagnetism. Its performance was evaluated by the magnetic solid-phase extraction of some neonicotinoid insecticides from water and fatmelon samples followed by high-performance liquid chromatographic analysis. The effects of the main experimental parameters that could affect the extraction efficiencies were investigated. The results demonstrated that the Co-MNPC had an excellent adsorption capability for the compounds.

Online Monitoring of Methanol Electro-Oxidation Reactions by Ambient Mass Spectrometry

AbstractOnline detection of methanol electro-oxidation reaction products [e.g., formaldehyde (HCHO)] by mass spectrometry (MS) is challenging, owing to the high salt content and extreme pH of the electrolyte solution as well as the difficulty in ionizing the reaction products. Herein we present an online ambient mass spectrometric approach for analyzing HCHO generated from methanol electro-oxidation, taking the advantage of high salt tolerance of desorption electrospray ionization mass spectrometry (DESI-MS). It was found that HCHO can be detected as PhNHNH+=CH2 (m/z 121) by DESI after online derivatization with PhNHNH2. With this approach, the analysis of HCHO from methanol electro-oxidation by MS was carried out not only in acidic condition but also in alkaline media for the first time. Efficiencies of different electrodes for methanol oxidation at different pHs were also evaluated. Our results show that Au electrode produces more HCHO than Pt-based electrodes at alkaline pH, while the latter have higher yields at acidic solution. The presented methodology would be of great value for elucidating fuel cell reaction mechanisms and for screening ideal fuel cell electrode materials. Graphical Abstractᅟ

Online Monitoring of Enzymatic Reactions Using Time-Resolved Desorption Electrospray Ionization Mass Spectrometry

Electrospray ionization mass spectrometry (ESI-MS) is powerful for determining enzymatic reaction kinetics because of its soft ionization nature. However, it is limited to use ESI-favored solvents containing volatile buffers (e.g., ammonium acetate). In addition, lack of a quenching step for online ESI-MS reaction monitoring might introduce inaccuracy, due to the possible acceleration of reaction in the sprayed microdroplets. To overcome these issues, this study presents a new approach for online measuring enzymatic reaction kinetics using desorption electrospray ionization mass spectrometry (DESI-MS). By using DESI-MS, enzymatic reaction products in a buffered aqueous media (e.g., a solution containing Tris buffer or high concentration of inorganic salts) could be directly detected. Furthermore, by adjusting the pH and solvent composition of the DESI spray, reaction can be online quenched to avoid the postionization reaction event, leading to fast and accurate measurement of kinetic constants. Reaction time control can be obtained simply by adjusting the injection flow rates of enzyme and substrate solutions. Enzymatic reactions examined in this study include hydrolysis of 2-nitrophenyl-β-D-galactopyranoside by β-galactosidase and hydrolysis of acetylcholine by acetylcholinesterase. Derived Michaelis-Menten constants Km for these two reactions were determined to be 214 μM and 172 μM, respectively, which are in good agreement with the values of 300 μM and 230 μM reported in literature, validating the DESI-MS approach. Furthermore, this time-resolved DESI-MS also allowed us to determine Km and turnover number kcat for trypsin digestion of angiotensin II (Km and kcat are determined to be 6.4 mM and 1.3 s-1, respectively).

Hollow fiber-based solid–liquid phase microextraction combined with theta capillary electrospray ionization mass spectrometry for sensitive and accurate analysis of methamphetamine

This paper presents a new method for quantitative analysis of methamphetamine (MAP) in urine samples based on hollow fiber-based solid–liquid phase microextraction (HF-SLPME) in combination with theta capillary-electrospray ionization mass spectrometry (TC-ESI-MS) detection. In the lumen of the hollow fiber, metal organic frameworks/graphene oxide (MOF/GO) hybrid material dispersed in 1-octanol was used as the acceptor phase for the enrichment of MAP. For TC-ESI-MS detection, the ESI emitter has a theta capillary with two separate channels and one common emitter tip. The MAP solution and the reference dopamine solution were separately loaded into the two channels. The ratio of signal intensities between MAP and dopamine was used for the evaluation of the extraction efficiency. Several experimental parameters influencing the extraction efficiency were investigated and optimized. Under the optimized conditions, the limit of detection was 0.5 ng mL−1, and the linearity range was 2.0–200.0 ng mL−1, with the correlation coefficient (R2) at 0.9997, indicating that the method based on HF-SLPME combined with TC-ESI-MS is sensitive and accurate for the determination of MAP in urine samples and would have utility in other types of trace chemical analyses.

ZIF-67 Templated Synthesis of Nanoporous Carbon as an Efficient Adsorbent for Preconcentration of Flunitrazepam from Beverage Samples

In this work, a nanoporous carbon (denoted as Co-NC) with high surface area, large pore volumes, strong magnetic response, and good graphitization degree was prepared using zeolitic imidazole framework (ZIF-67) as both a precursor and a template without any additional carbon source. Scanning electron microscopy, transmission electron microscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy, vibrating sample magnetometer, and N2 adsorption were used to characterize the Co-NC. The Co-NC was explored as the magnetic adsorbent, and its adsorption performance was evaluated by extraction of flunitrazepam from beverage samples. Several experimental parameters affecting the extraction efficiencies were investigated and optimized. The results confirmed that the Co-NC showed an excellent adsorption capacity for flunitrazepam.

Highly sensitive mass spectrometric detection of flunitrazepam using magnetic graphene framework enrichment

In this paper, a magnetic graphene framework (MGF) material was prepared and used as a magnetic solid-phase extraction adsorbent for the preconcentration of flunitrazepam from beverage samples prior to high resolution mass spectrometric determination. The MGF nanocomposite was characterized by scanning electron microscopy, transmission electron microscopy, vibrating sample magnetometry, and N2 adsorption. The high surface area and specific framework structure of the MGF endows it with a high adsorption capacity. Several experimental parameters affecting the extraction efficiencies, such as the amount of the adsorbent, extraction time, sample pH and desorption conditions were optimized. Under the optimum conditions, a good linearity was achieved in the concentration range of 0.01–1.0 nmol L−1 for ginger ale and 0.05–5.0 nmol L−1 for the Pure tea sample with the correlation coefficients larger than 0.9875. The limits of detection of the method were 0.001 nmol L−1 (0.3 ng L−1) for ginger ale and 0.005 nmol L−1 (1.5 ng L−1) for Pure tea, which is about 3–4 orders of magnitude lower than those of literature reports. The recoveries of the method for the analytes were in the range of 92.0–102.5%. The results indicated that the developed method was efficient for the preconcentration of trace levels of flunitrazepam from beverage samples. The MGF adsorbent would have a significant application potential for the enrichment of other abused drugs and organic pollutants in different samples.