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Mass spectrometry (MS) has become an essential analytical method in every sector of science and technology. Because of its unique ability to provide direct molecular structure information on analytes, an extra method is rarely required. This review describes fabrication of a variable-pressure hollow cathode discharge (HCD) ion source for MS in detection, quantification and investigation of gas-phase ion molecule reactions of explosives and related compounds using air as a carrier gas. The HCD ion source has been designed in such a way that by altering the ion source pressures, the system can generate both HCD and conventional GD. This design enables for the selective detection and quantification of explosives at trace to ultra-trace levels. The pressure-dependent HCD ion source has also been used to investigate ion-molecule reactions in the gas phase of explosives and related compounds. The mechanism of ion formation in explosive reactions is also discussed. [ABSTRACT FROM AUTHOR]

Ambient ionization mass spectrometry (AIMS) is an emerging onsite rapid detection technique that has been applied in the area of public security. AIMS measurements of samples with complex matrices are characterized by poor reproducibility and complexity. Low reproducibility and complex background cause imprecise screening for trace drugs in hair. In this work, a rapid screening method of methamphetamine in hair is proposed. Firstly, the generalized weighted robust principal component analysis (GWRPCA) algorithm is used to remove background and extract the analytical signals. The similarity scores between the analytical signals and standard mass spectrum of methamphetamine were calculated based upon an improved Pearson's correlation coefficient combined with the preset matching threshold to achieve rapid screening of methamphetamine in hair. The results show that this method accurately screens for this drug hair and identifies actual false positives with 100% accuracy when the analyte threshold was 0.1 ng/mg and the matching threshold was 0.6. This study provides technical support for the rapid screening for drug abuse by AIMS. [ABSTRACT FROM AUTHOR]

A simple, effective, and highly sensitive analytical approach was created and applied in this study for the accurate measurement of three β2-agonist residues (clenbuterol, salbutamol, and ractopamine) in meat samples. In the course of the experiment, new adsorbent molecular sieves (ZMS)@nitrogen-doped carbon quantum dots (N-CQDs) composite materials were synthesized with the aid of hydrothermal synthesis. The composite adsorbent materials were prepared and characterized through scanning electron microscopy, transmission electron microscope, X-ray photoelectron spectroscopy, fluorescence, and zeta potential. Four determinants affecting the extraction and elution's efficiency, such as the amount of adsorbent, the extraction time, desorption time, and the amount of extraction salt, were substantially optimized. The analytes were quantified by gas chromatography–mass spectrometry. Final results of the methodological validation reflected that the ZMS@N-CQDs composite materials were able to adsorb three β2-agonist residues well and had good reproducibility. In the meantime, all analytes indicated good linearity with coefficient of determination R2 ≥ 0.9908. The limit of detection was 0.7–2.0 ng·g−1, the limit of quantification varied from 2.4 to 5.0 ng·g−1, the precision was lower than 11.9%, and the spiked recoveries were in the range of 79.5–97.8%. To sum up, the proposed approach was quite effective, reliable, and convenient for the simultaneous analysis of multiple β2-agonist residues. Consequently, this kind of approach was successfully applied for the analysis of such compounds in meat samples. [ABSTRACT FROM AUTHOR]

The abuse of fentanyl and its analogs has caused a large number of deaths worldwide. Due to the rapid development of new fentanyl analogs, the standard mass spectral library is generally incomplete. The spectra obtained by different mass spectrometers by electrospray ionization (ESI) cannot be used across platforms, resulting in the hysteretic detection of novel fentanyl analogs. This paper reports a machine learning classification model based upon a hybrid similarity search. For the purpose of the identification of fentanyl analogs with different mass spectrometers, a mass spectral library based on the conserved fragmentation behavior (CFB) of fentanyl analogs was established. The results show that the identification accuracy of fentanyl analogs by two mass spectrometers is 100%, and the accuracy of classification model is 97.85%. Furthermore, the model may be applied to linear ion trap mass spectrometry (LIT-MS) and quadrupole time-of-flight mass spectrometry (Q-TOF-MS) with classification accuracies of 100 and 98.17%, respectively. This study provides promising technical support for the real-time and cloud computing detection of unknown fentanyl analogs. [ABSTRACT FROM AUTHOR]

Development of nano‐structured metal oxides/heteroatom composites with controlled components and structure for photochemical oxidation still remains a great challenge. Here, a new and versatile strategy is reported for transformation of organonitrogen‐encapsulated metal‐organic frameworks (MOFs) into N‐doped Fe3O4@C nanopolyhedron by chemical vapor deposition‐induced super‐assembly method. Strong confined interaction between organonitrogen guests (urea, thiourea, melamine, and dimethylimidazole) and Fe nodes of MOFs realizes reconstruction of crystal structure and introduction of N species. With the novel approach, the uniform dispersion of guests and perfect metallic/heteroatom interfacial is obtained. Compared with MOFs‐derived Fe2O3/C, the heteroatom/defect‐to‐metal cluster charge transfer excitations lead N‐doped Fe3O4@C to exhibit more superior activity for photocatalytic oxidation (turn‐over frequencies as high as 3.72 h−1). It demonstrates that the introduction of abundant pyrrole‐N and oxygen vacancies on carbon interface boosts the advance of photo‐generated carrier transfer. The study offers a simple and promising strategy for the design of novel metal oxides/heteroatom composite with adjustable structure and functions. [ABSTRACT FROM AUTHOR]

The controllable preparation of crystals is a prerequisite for exploring their shape-dependent physicochemical properties. Herein, AgCl crystals with different morphologies including octahedron, trapezohedron (TPH), 12-pod and hexapods with mace pods were successfully prepared by a one-pot synthesis method. In the preparation process, ethylene glycol (EG) was used as a solvent and AgNO3 was used as a precursor of Ag+. In particular, the ionic liquid poly(diallyldimethylammonium chloride) (PDDA) not only acted as a Cl− ion precursor but also as a morphology-controlled stabilizer. We further explored the effects of temperature, ligand and precursor concentration on AgCl crystal growth. Moreover, we investigated the effect of Cl− concentration on the morphology of AgCl by adding different amounts of NaCl. We found that under the condition of the lower concentrations of Cl−, {111}-bound octahedral AgCl crystals will transform into TPH enclosed with the {311} facet as the concentration of Cl− ions increases. However, at medium concentrations of Cl−, {111}-bound octahedral AgCl crystals will transform into 3D 12-pod AgCl crystals as the concentration of Cl− ions increases. Under the condition of higher concentrations of Cl−, {111}-bound octahedral AgCl crystals will transform into hexapods with mace pods AgCl crystals as the concentration of Cl− ions increases. According to the experimental results, we proposed the growth mechanism of AgCl microcrystals. This work not only provides a new method for the synthesis of AgCl crystals with a tunable shape, but also helps to understand the crystal growth mechanism. [ABSTRACT FROM AUTHOR]