BiOCl Nanosheets with (001), (002), and (003) Dominant Crystal Faces with Excellent Light-Degradation Ability.

Gray bismuth chloride nanosheets with a highly enhanced electric field intensity were prepared by a simple and efficient method. Their energy gap is reduced to 2.35 eV. The prepared nanosheets show high photocatalytic activity for the degradation of rhodamine B under visible light. The resulting samples were characterized by X-ray diffractometry, high-resolution scanning electron microscopy, X-ray photoelectron spectroscopy, infrared spectroscopy, UV-vis diffuse reflectance spectroscopy, specific surface area analysis, electrochemical analysis, electron paramagnetic resonance, and UV-vis spectroscopy. The photocatalytic activity of prepared BiOCl was evaluated by the degradation of RhB. The prepared BiOCl sample (0.5 g/L) could completely degrade RhB (10 mg/L) within 10 min, and its visible photocatalytic activity was 80 times that of the original white BiOCl. Superoxide radicals were the main active substance involved in organic degradation.

Dilemmas and options for COVID-19 vaccination in children.

Over 16 million children have been detected positive for the coronavirus disease 2019 (COVID-19) in the United States since the outbreak of the pandemic. In general, children infected with severe acute respiratory syndrome coronavirus type 2 tend to have lighter symptoms than adults. However, in some cases, the infection can develop into severe forms, such as multisystem inflammatory syndrome in children. Moreover, long-term public health preventive interventions have had some negative effects on the physical and mental health of children. Given the important role that vaccination plays in reducing severe illness and mortality, it is essential for the efficient implementation of vaccination in the pediatric population. Nevertheless, parental distrust of vaccination, especially with regard to its safety and efficacy, hinders this process. Herein, we comprehensively summarize the available data on the safety and effectiveness of COVID-19 vaccine in children. The results show that the currently approved COVID-19 vaccine is safe and effective for children. Although two doses of vaccine in children seem insufficient to prevent Omicron infection, the booster dose provides enhanced protection against infection and severe illness. Most importantly, the bivalent vaccine has been approved for use in the pediatric population to extend the immune response to currently circulating Omicron variant. And the immune protection afforded to newborns after maternal vaccination appears to last only 6 months. Therefore, in the current situation where the rate of virus mutation is accelerating and the COVID-19 pandemic is still severe, it is crucial to extend vaccine protection to children over 6 months of age to weave a tighter safety net.

Simultaneous qualitative and quantitative analyses of volatile components in Chinese honey of six botanical origins using headspace solid-phase microextraction and gas chromatography-mass spectrometry.

BACKGROUND: Honey aroma is one of its most important properties and it depends on the qualitative and quantitative composition of the volatile compounds. The volatile profile of honey could reveal its botanical origin to avoid a false characterization. Thus, it is of great significance to honey authentication. This study developed and validated a headspace solid-phase microextraction and gas chromatography-mass spectrometry (HS-SPME-GC-MS) method for simultaneous qualitative and quantitative analyses of 34 volatile components in honey. The developed method was applied to 86 honey samples from six different botanical origins, including linden honey, rape honey, jujube honey, vitex honey, lavender honey and acacia honey. RESULTS: The volatile fingerprints and quantitative results were simultaneously obtained by using the full scan and selected ion monitoring (SCAN+SIM) MS scanning mode. The limits of quantification (LOQs) and limits of detection (LODs) of 34 volatile compounds were in the ranges of 1-10 ng/g and 0.3-3 ng/g, respectively. And the spiked recoveries ranged between 70.6% and 126.2%, with the relative standard deviations (RSDs) not higher than 45.4%. A total of 98 volatile compounds were found with relative contents determined, and the 34 volatile compounds were determined with absolute concentrations. Based on the volatile fingerprints and the contents of volatile compounds, honey samples from six botanical origins were well classified by principal component analysis and orthogonal partial least-squares discrimination analysis. CONCLUSIONS: The HS-SPME-GC-MS method was successfully applied to achieve the volatile fingerprints of six types of honey and to quantitatively analyze 34 volatile compounds with satisfying sensitivity and accuracy. Chemometrics analysis showed significant correlations between honey types and volatiles. These results reveal the characteristics of volatile compounds in six types of unifloral honey and provide some supports for honey authentication. © 2023 Society of Chemical Industry.

Single-Photon Ionization Mass Spectrometry Using a Vacuum Ultraviolet Femtosecond Laser.

The wavelength of a femtosecond Ti:sapphire laser (TS, 800 nm) was converted into the ultraviolet (UV, 200 nm) using three ß-barium borate crystals (ß-BaB2O4) for frequency doubling and subsequent mixing. The UV pulse was further converted into the vacuum ultraviolet (VUV, 185 nm) based on four-wave Raman mixing, in which a two-color pump beam consisting of the fundamental beam (800 nm) of the TS and the signal beam of an optical parametric amplifier (1200 nm) pumped by the TS was focused onto a capillary waveguide filled with hydrogen gas for molecular phase modulation and the single-color UV probe beam (200 nm) was then focused onto the waveguide for frequency modulation to generate anti-Stokes and high-order Stokes Raman sidebands at wavelengths of 185 and 218-267 nm, respectively. The efficiency of conversion from the UV (200 nm) to the VUV (185 nm) was 6%. The ionization energy was calculated for 13 amino polycyclic aromatic hydrocarbons using density functional theory, since they are associated with the development of occupational bladder cancers. The values calculated by the B3LYP/cc-pVDZ and ωB97Xd/cc-pVTZ methods were 6.24-7.14 eV (199-174 nm) and 6.41-7.35 eV (194-169 nm), respectively. A sample containing a mixture of 9-aminoanthracene, 3-aminofluoranthene, and 1-aminopyrene was separated by gas chromatography (GC), and the eluents were ionized with the VUV pulse (0.015 µJ) in mass spectrometry (MS). The analytes were observed on a two-dimensional display of GC/MS, and the detection limit obtained by single-photon ionization of 3-aminofluoranthene was 1 ng/µL.

Simultaneous determination of seven perfluoroalkyl carboxylic acids in water samples by 2,3,4,5,6-pentafluorobenzyl bromide derivatization and gas chromatography-mass spectrometry.

A new derivatization reagent, 2,3,4,5,6-pentafluorobenzyl bromide (PFBBr), was employed to determine seven perfluoroalkyl carboxylic acids (PFCAs) simultaneously in tap water with gas chromatography-mass spectrometry (GC-MS) technique in this study. Firstly, seven PFCAs were derivatized to their corresponding esters under alkaline condition. The derivatization conditions including the amount of PFBBr and K2CO3, derivatization temperature and time were optimized to increase the derivatization efficiency. The 14 tap water samples collected from different places of China were enriched and purified through solid phase extraction pretreatment. The limits of detection (LODs) and the limits of quantitation (LOQs) ranged from 0.1 ng/L to 0.28 ng/L and from 0.3 ng/L to 0.84 ng/L, respectively. The new method offers a linear relationship in the range from 2 ng/L to 2000 ng/L, and the correlation coefficients ranged from 0.9938 to 0.9994. The results showed that GC-MS combined with pre-column derivatization is a reliable method for the analysis of PFCAs in the aqueous environment.

Simultaneous determination of nine perfluoroalkyl carboxylic acids by a series of amide acetals derivatization and gas chromatography tandem mass spectrometry.

A novel and simple derivatization method using a series of amide acetals as derivatization reagents, along with gas chromatography tandem mass spectrometry (GC-MS/MS) analysis, were developed and validated for simultaneous determination of 9 perfluoroalkyl carboxylic acids (PFCAs) in this study. The structures and fragmentation pathway of PFCAs derivatives were deduced and verified. The derivatization method developed in this study improved the sensitivity of the detection of PFCAs by GC. The applicability of 6 amide acetals for the derivatization of PFCAs was demonstrated. Derivatization conditions for 9 PFCAs were optimized with addition of 20 µL of derivatization reagent and reaction at 35 °C for 30 min. 9 PFCAs derivatives were confirmed to be stable over 15 days. The instrument detection limits (IDLs) were lower than 0.01 pg/µL. The intra and inter-day precisions were below 4.06% and 5.48%, respectively. To demonstrate the utility of the derivatization method, the level of PFCAs in the marine products were detected. The alkaline digestion followed by solid-phase extraction (SPE) cleanup method was used for pretreatment. The method detection limits (MDLs) ranged from 0.04 to 0.10 ng/g, and the spiked recoveries ranged between 54.72% and 107.29%, with relative standard deviation (RSD) of 1.53%-11.89%. Five PFCAs were detected in the range of 0.66 to 499.03 ng/g dry weight.

Optimal Laser Wavelength for Femtosecond Ionization of Polycyclic Aromatic Hydrocarbons and Their Nitrated Compounds in Mass Spectrometry.

The ionization and fragmentation processes were examined for a standard sample mixture containing 16 polycyclic aromatic hydrocarbons (PAHs) and 3 nitro-PAHs (NPAHs) by gas chromatography combined with mass spectrometry (GC/MS) using a femtosecond laser emitting at 400, 800, or 1200 nm as the ionization source. The signal intensities of NPAHs were lower and the fragmentation more extensive compared to those values for PAHs, especially at shorter wavelengths (400 nm). These results can be explained by efficient intersystem crossing to triplet levels and the shorter excited-state lifetimes of neutral NPAHs molecules, compared to the pulse width of the laser. Fragmentation was significantly suppressed by nonresonant multiphoton ionization when a laser emitting at longer wavelengths (1200 nm) was used. This result can be explained by the absorption spectrum of the molecular ion and the excess energy remaining in the ionized state. In fact, there was no absorption band at 1200 nm for the molecular ion, and the excess energy would be minimal when a near-infrared laser is used, which suppresses the fragmentation even for NPAHs. A doubly charged molecular ion was observed for PAHs but not for NPAHs, probably owing to the higher stability of the PAH molecule, the electrons of which are more strongly bound and are more resistive to field ionization. To demonstrate the utility of this technique, the sample extracted from particulate matter 2.5 (PM2.5) emitted from a diesel engine was measured. NPAHs as well as PAHs were clearly determined at 1200 nm, at which the background signal arising from the interference was drastically suppressed.

Suppression of fragmentation in multiphoton ionization mass spectrometry using a near-infrared femtosecond laser as an ionization source.

The ionization and fragmentation processes for pentachlorobenzene were examined using a femtosecond laser emitting at 400, 800, and 1200 nm. A molecular ion was clearly observed in the mass spectrum, since the molecule can be directly ionized from the singlet electronic exited state before relaxation to triplet levels, because the pulse width of the laser is shorter than the lifetime of the excited state. Fragmentation was minimal at 1200 nm, in contrast to ionization at 800 and 400 nm. Indeed, a doubly-charged molecular ion was prominent at 800 nm, owing to the absorption band of the singly-charged molecular ion at this wavelength. Fragmentation was further enhanced at 400 nm, which can be explained by the dissociation of the doubly-charged molecular ion having a larger absorption band at 400 nm. Fragmentation was strongly affected by the absorption character of the ionic species, i.e., singly- and doubly-charged molecular ions, appeared in the process of multiphoton ionization.

Determination of Nerve Agent Metabolites by Ultraviolet Femtosecond Laser Ionization Mass Spectrometry.

Nerve agent metabolites, i.e., isopropyl methylphosphonic acid (IMPA) and pinacolyl methylphosphonic acid (PMPA), were derivatized by reacting them with 2,3,4,5,6-pentafluorobenzyl bromide (PFBBr) and were determined by mass spectrometry using an ultraviolet femtosecond laser emitting at 267 and 200 nm as the ionization source. The analytes of the derivatized compounds, i.e., IMPA-PFB and PMPA-PFB, contain a large side-chain, and molecular ions are very weak or absent in electron ionization mass spectrometry. The use of ultraviolet femtosecond laser ionization mass spectrometry, however, resulted in the formation of a molecular ion, even for compounds such as these that contain a highly bulky functional group. The signal intensity was larger at 200 nm due to resonance-enhanced two-photon ionization. In contrast, fragmentation was suppressed at 267 nm (nonresonant two-photon ionization) especially for PMPA-PFB, thus resulting in a lower background signal. This favorable result can be explained by the small excess energy in ionization at 267 nm and by the low-frequency vibrational mode of a bulky trimethylpropyl group in PMPA.

Internal standards for use in the comprehensive analysis of polychlorinated aromatic hydrocarbons using gas chromatography combined with multiphoton ionization mass spectrometry.

To decrease health-risks to humans, non-toxic compounds were evaluated for use as internal standards for calibrating data obtained by gas chromatography/multiphoton ionization mass spectrometry (GC-MPI-MS) using an ultraviolet femtosecond laser as the ionization source. The retention time in the mass chromatogram was calibrated using a retention index, in which a series of n-alkanes was employed as internal standards for evaluating the retention times for polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and polychlorinated biphenyls (PCBs). To compensate for changes in signal intensity in MPI-MS, the dependence of signal intensity on the laser pulse energy was investigated for the dioxin-like compounds, in addition to five non-toxic aromatic hydrocarbons, that were used as internal standards. Based on their similar behavior,the non-toxic PCDD/PCDF, its 13C-isotope, and pentachlorobenzene behave similarly, we conclude that they can be used for calibrating the signal intensities in MPI-MS.

Determination of Hexachlorocyclohexane by Gas Chromatography Combined with Femtosecond Laser Ionization Mass Spectrometry.

Structural isomers and enantiomers of hexachlorocyclohexane (HCH) were separated using a chiral column by gas chromatography and quantitatively determined by multiphoton ionization mass spectrometry using an ultraviolet femtosecond laser (200 and 267 nm) as the ionization source. The order of elution of the enantiomers (i.e., (+)-α-HCH and (-)-α-HCH) was predicted from stabilization energies calculated for the complexes using permethylated γ-cyclodextrin as the stationary phase of the column, and the results were compared with the experimental data. The molecular ions observed for HCH were weak, even though they can be ionized through a process of resonance enhanced two-photon ionization at 200 nm. This unfavorable result can be attributed to the dissociation of the molecular ion, as predicted from quantum chemical calculations. Graphical Abstract ᅟ.

[Simultaneous determination of cyhexatin, triphenyltin and fenbutatin oxide residues in fruits and vegetables by Grignard derivatization and gas chromatography coupled to tandem mass spectrometry].

A method for the simultaneous determination of cyhexatin, triphenyltin and fenbutatin oxide residues in fruits and vegetables was developed by Grignard derivatization and gas chromatography coupled to tandem mass spectrometry (GC-MS/MS). The samples were firstly digested by HC1/THF (1 :10, v/v), then extracted by hexane and followed by the derivatization with Grignard reagent (EtMgBr). Then after purification using florisil SPE columns, the sample extracts were finally analyzed by GC-MS/MS. The qualitative and quantitative determinations of the three organotin pesticides were performed by the tandem mass in multiple reaction monitoring (MRM) mode. By using apple as a representative matrix, the limits of detection (LODs) obtained by the proposed method for cyhexatin, triphenyltin and fenbutatin oxide were 2. 0, 1. 5 and 3.4 µg/kg (as Sn), respectively. The average recoveries for the three organotin pesticides were in the range of 72.4%-107. 1% at the spiked levels of 10, 20, 50 and 200 µg/kg (as Sn) and the relative standard deviations (RSDs) ranged from 0. 4% to 14. 2%. The proposed method was validated to have good linearity, high sensitivity, selectivity and accuracy for the simultaneous determination of cyhexatin, triphenyltin and fenbutatin oxide in fruits and vegetables. The sensitivity of this method can meet the requirements of the inspection for the three organotin pesticides at the level of maximum residue limits (MRLs) set by China and some other countries.

Analysis of pesticides by gas chromatography/multiphoton ionization/mass spectrometry using a femtosecond laser.

Gas chromatography/multiphoton ionization/time-of-flight mass spectrometry (GC/MPI/TOFMS) was utilized for analysis of a standard mixture sample containing 49 pesticides and 4 real samples using the third-harmonic emission (267 nm) of a femtosecond Ti:sapphire laser (100 fs) as the ionization source. A sample of a standard mixture of n-alkane was also measured for calibration of the retention time indices of the pesticides. Two photons are required for the excitation of n-alkane due to an absorption band located in the far ultraviolet region (140 nm). The n-alkane molecule in the excited state was subsequently ionized either directly or by absorbing another photon because of a high ionization potential. Due to a large excess of energy, the molecular ion was decomposed and formed many fragment ions. Compared to n-alkanes, most of the pesticides were softly ionized by the femtosecond laser; one photon was used for excitation and another was used for the subsequent ionization. The pesticides with no conjugated double bond had a lower ionization efficiency. The present analytical instrument was applied to several samples prepared from a variety of vegetables and a single fruit after pretreatment with solid-phase extraction. Three pesticides were found in these samples, although some of them were not detected by conventional GC/EI/MS-MS due to insufficient sensitivity and selectivity.

Analysis of dioxins by gas chromatography/resonance-enhanced multiphoton ionization/mass spectrometry using nanosecond and picosecond lasers.

Dioxins in a soil sample were measured using gas chromatography/resonance-enhanced multiphoton ionization/time-of-flight mass spectrometry coupled with different types of laser sources. The fourth-harmonic emission (266 nm) of a nanosecond Nd:YAG laser (1 ns) provided low ionization efficiency, especially for highly chlorinated dioxins/dibenzofurans (CDDs/CDFs). The ionization efficiency was improved using the fourth-harmonic emission (266 nm) of a picosecond Nd:YAG laser (4 ps), due to shorter singlet excited-state lifetimes. It was, however, difficult to efficiently ionize hepta-CDD and octa-CDD/CDF, because of their shorter lifetimes, which were induced by stronger spin-orbit coupling that led to efficient relaxation of the excited molecule to triplet levels. The ionization efficiency was substantially improved using the fifth-harmonic emission (213 nm) of the picosecond Nd:YAG laser (4 ps), in which the analyte molecule that was relaxed to triplet levels was efficiently ionized using a photon with sufficient energy for ionization, although the pulse energy obtained at 213 nm was only one-third of the pulse energy obtained at 266 nm. The limits of detection achieved for 17 toxic polychlorinated dibenzo-p-dioxins/polychlorinated dibenzofurans (PCDDs/PCDFs) were 0.41-45 pg. The analytical instrument developed in the present study performed sufficiently well for the practical trace analysis of dioxins in soil samples.

Trace analysis of polycyclic aromatic hydrocarbons using gas chromatography-mass spectrometry based on nanosecond multiphoton ionization.

Gas chromatography/resonance-enhanced multiphoton ionization/time-of-flight mass spectrometry (GC/REMPI-TOFMS) using an ultraviolet nanosecond laser was employed in the trace analysis of polycyclic aromatic hydrocarbons (PAHs). A standard sample that contained 16 PAHs on the priority list of the Environmental Protection Agency of the United States of America (U.S. EPA) was measured. A sample of river water that had been pretreated by means of solid-phase extraction was analyzed by GC/MS based on electron impact ionization (EI) and REMPI to evaluate the performance of the analytical instrument. The results suggested that REMPI is superior to EI for soft ionization, and suppresses the background signal due to aliphatic hydrocarbons. Thus, GC/REMPI-TOFMS is a more reliable method for the determination of PAHs present in the environment.