The use of barium (II) to promote triplet←singlet transitions in organic compounds; an external heavy-atom effect

The possibility of using barium (II) to promote spin forbidden transitions is examined. Methanolic solutions of both quinoline and naphthalene in the presence of perchlorate reveal weak bands in their electronic absorption spectra which are assigned to the lowest triplet←singlet transitions. Barium (II) is also found to quench the fluorescence of naphthalene, probably as a result of a heavy atom effect.     

Does the concept of Clar's aromatic sextet work for dicationic forms of polycyclic aromatic hydrocarbons?--testing the model against charged systems in singlet and triplet states

The concept of Clar's π-electron aromatic sextet was tested against a set of polycyclic aromatic hydrocarbons in neutral and doubly charged forms. Systems containing different types of rings (in the context of Clar's concept) were chosen, including benzene, naphthalene, anthracene, phenanthrene and triphenylene. In the case of dicationic structures both singlet and triplet states were considered. It was found that for singlet state dicationic structures the concept of aromatic sextet could be applied and the local aromaticity could be discussed in the context of that model, whereas in the case of triplet state dicationic structures Clar's model rather failed. Different aromaticity indices based on various properties of molecular systems were applied for the purpose of the studies. The discussion about the interdependence between the values of different aromaticity indices applied to neutral and charged systems in singlet and triplet states is also included.     

Formation of cation–radical anion pairs derived from carboxybenzophenone–tetrabutylammonium salts. Pulse radiolysis studies

Pulse radiolysis of acetonitrile solutions of tetra-n-butyl ammonium salts of 2- and 4-carboxybenzophenones [BP-COO⁻···N⁺(C₄H₉)₄] were performed in order to generate directly the reduced forms of the benzophenone moieties within pre-formed ion pairs. In earlier studies on photochemical electron transfer reactions, ion pairs containing a tetraalkyl ammonium cation and a benzophenone radical anion were formed in an electron transfer to the triplet BP from a quencher consisting of a tetraalkyl ammonium salt of (phenylthio)acetic acid. In the current work, the [BP^•−COO⁻···N⁺(C₄H₉)₄] ion pairs were formed by direct reduction of the salts without the complication of a third moiety, i.e., the (phenylthio)acetic anion. The spectra and kinetic parameters of the radiolytically-reduced salts were compared to the behavior of reduced forms of the 2- and 4-COOH substituted benzophenones. The results from the pulse radiolysis and photochemistry were compared and explained in terms of the different structures of the ion pairs.     

In-line solid-phase extraction–capillary electrophoresis coupled with mass spectrometry for determination of drugs of abuse in human urine

In-line solid-phase extraction–capillary electrophoresis coupled with mass spectrometric detection (SPE–CE–MS) has been used for determination of 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP), codeine (COD), hydrocodeine (HCOD), and 6-acetylmorphine (6AM) in urine. The preconcentration system consists of a small capillary filled with Oasis HLB sorbent and inserted into the inlet section of the electrophoresis capillary. The SPE–CE–MS experimental conditions were optimized as follows: the sample (adjusted to pH 6.0) was loaded at 930 mbar for 60 min, elution was performed with methanol at 50 mbar for 35 s, 60 mmol L⁻¹ ammonium acetate at pH 3.8 was used as running buffer, the separation voltage was 30 kV, and the sheath liquid at a flow rate of 5.0 μL min⁻¹ was isopropanol–water 50:50 (v/v) containing 0.5% acetic acid. Analysis of urine samples spiked with the four drugs and diluted 1:1 (v/v) was studied in the linear range 0.08–10 ng mL⁻¹. Detection limits (LODs) (S/N = 3) were between 0.013 and 0.210 ng mL⁻¹. Repeatability (expressed as relative standard deviation) was below 7.2%. The method developed enables simple and effective determination of these drugs of abuse in urine samples at the levels encountered in toxicology and doping.     

A simple method of target preparation for the bulk analysis of powder samples by laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS)

A simple and rapid procedure using a glue technique has been developed for the preparation of stable targets from powder samples for bulk analysis by LA– ICP–MS. The procedure was evaluated for the analysis of trace elements in SiC, of rare-earth elements in different types of silicate (rocks, sediments, and soils), and of Au and platinum-group elements in geological silicates. The test analysis was conducted using an IR laser in combination with a quadrupole mass spectrometer. The recommended preparation procedure offers the possibility of different types of calibration, for example application of certified reference samples in combination with prepared spiked samples on a base of a natural or synthetic matrix, or addition calibration. The resulting calibration functions are linear over a range of several decades. The trueness of the results was evaluated by use of certified reference samples. Analytical concentration ranges, detection limits, and the relative standard deviations are reported. Received: 20 November 2000 / Revised: 13 March 2001 / Accepted: 17 March 2001     

μLC coupled to ICP–SFMS with post-column isotope dilution analysis of sulfur for absolute protein quantification

Absolute protein quantification has become an important challenge in modern bioanalytical chemistry. Among several approaches based on mass spectrometric techniques, inductively coupled plasma (ICP) as ionisation source provides element-selective and sensitive detection of heteroatoms, and thus, a potentially emerging tool in protein analysis. In this work we applied coupling of capillary liquid chromatography (μLC) and inductively coupled plasma-sector field mass spectrometry (ICP–SFMS) to the separation and determination of standard proteins. For quantification purposes, post-column isotope dilution of sulfur was applied and optimised for this type of hyphenated technique. Provided that the protein sequence is known (number of sulfur-containing amino acids, i.e. cysteines and methionines) the protein amount can then be directly calculated from the determined sulfur content in a certain protein fraction. In order to prove the reliability of the presented method, two different certified reference materials were analysed: CRM 393 (human apolipoprotein A-I) and CRM 486 (α-fetoprotein). For CRM 393 excellent agreement (37.0 ± 1.4 μmol L⁻¹) was obtained with the certificate (37.7 ± 1.8 μmol L⁻¹). However, the recovery rate for α-fetoprotein in CRM 486 was found to be about 60% indicating incomplete elution of the protein during the chromatographic separation.     

Screen-printed electrode-based electrochemical detector coupled with in-situ ionic-liquid-assisted dispersive liquid–liquid microextraction for determination of 2,4,6-trinitrotoluene

A novel method is reported, whereby screen-printed electrodes (SPELs) are combined with dispersive liquid–liquid microextraction. In-situ ionic liquid (IL) formation was used as an extractant phase in the microextraction technique and proved to be a simple, fast and inexpensive analytical method. This approach uses miniaturized systems both in sample preparation and in the detection stage, helping to develop environmentally friendly analytical methods and portable devices to enable rapid and onsite measurement. The microextraction method is based on a simple metathesis reaction, in which a water-immiscible IL (1-hexyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide, [Hmim][NTf₂]) is formed from a water-miscible IL (1-hexyl-3-methylimidazolium chloride, [Hmim][Cl]) and an ion-exchange reagent (lithium bis[(trifluoromethyl)sulfonyl]imide, LiNTf₂) in sample solutions. The explosive 2,4,6-trinitrotoluene (TNT) was used as a model analyte to develop the method. The electrochemical behavior of TNT in [Hmim][NTf₂] has been studied in SPELs. The extraction method was first optimized by use of a two-step multivariate optimization strategy, using Plackett–Burman and central composite designs. The method was then evaluated under optimum conditions and a good level of linearity was obtained, with a correlation coefficient of 0.9990. Limits of detection and quantification were 7 μg L^?1 and 9 μg L^?1, respectively. The repeatability of the proposed method was evaluated at two different spiking levels (20 and 50 μg L^?1), and coefficients of variation of 7 % and 5 % (n?=?5) were obtained. Tap water and industrial wastewater were selected as real-world water samples to assess the applicability of the method.

A colorimetric assay for measuring iodide using Au@Ag core–shell nanoparticles coupled with Cu

Au@Ag core–shell nanoparticles (NPs) were synthesized and coupled with copper ion (Cu²⁺) for the colorimetric sensing of iodide ion (I⁻). This assay relies on the fact that the absorption spectra and the color of metallic core–shell NPs are sensitive to their chemical ingredient and dimensional core-to-shell ratio. When I⁻ was added to the Au@Ag core–shell NPs-Cu²⁺ system/solution, Cu²⁺ can oxidize I⁻ into iodine (I₂), which can further oxidize silver shells to form silver iodide (AgI). The generated Au@AgI core–shell NPs led to color changes from yellow to purple, which was utilized for the colorimetric sensing of I⁻. The assay only took 10 min with a lowest detectable concentration of 0.5 μM, and it exhibited excellent selectivity for I⁻ over other common anions tested. Furthermore, Au@Ag core–shell NPs-Cu²⁺ was embedded into agarose gels as inexpensive and portable “test strips”, which were successfully used for the semi-quantitation of I⁻ in dried kelps.     

Particle-into-liquid sampler on-line coupled with solid-phase extraction-liquid chromatography–mass spectrometry for the determination of organic acids in atmospheric aerosols

In the present study, sample collection and preparation were directly integrated with a chromatographic system by coupling a particle-into-liquid sampler for the first time on-line with solid-phase extraction-liquid chromatography–tandem mass spectrometry. Several organic acids, such as adipic, hydroxyglutaric, mandelic, vanillic, cis-pinonic, pinic, azelaic and sebacic, were used in the research. For sample pretreatment and concentration, strong anion exchange material was used in the extraction. Sampling, extraction and analysis conditions were optimized to obtain reliable information about aerosol chemical composition. To evaluate the performance of the on-line coupled system, half of each sample was analysed on-line and the other half was derivatized and analysed off-line by gas chromatography–mass spectrometry. Comparison of the two techniques with use of t-test showed the results to be in an excellent agreement. Limits of detection of studied acids in on-line system were between 0.1 and 0.9 ng. The on-line coupled system is fast and reliable and a promising tool for the real time analysis of organic acids in atmospheric aerosols.     

Thiophene–nitroxide radical as a novel combination of sensitizer–redox mediator for dye-sensitized solar cells

We report a novel combination of organic sensitizer and redox mediator in the electrolyte for dye-sensitized solar cells (DSSCs): a thiophene dye and nitroxide radicals. Nitroxide radicals and their oxidized counterparts of oxoammonium cations show robust reversible redox reactions, thus supporting robust DSSC operations. Moreover, their redox potentials (E _1/2) and thus open-circuit voltages (V _OC) can be tuned further by attached functional groups. Optical and electrochemical characterization reveal that these new combinations exhibit enhanced V _OC and power conversion efficiencies compared to the existing iodine mediator (I⁻/I₃⁻) due to the increased V _OC. Also, the selection of the sensitizer–redox mediator turns out to be critical in the overall cell performance. Indeed, the typical ruthenium dye loses its light absorption capability when it is operated in conjunction with the nitroxide radicals.     

Development and validation of volumetric absorptive microsampling coupled with UHPLC–MS/MS for the analysis of gamma-hydroxybutyric acid in human blood

A volumetric microsampling (VAMS) device (20 μl) was evaluated and validated for the analysis of γ-hydroxybutyric acid (GHB) in venous blood using a simple ultra-high-pressure liquid chromatography–tandem mass spectrometry (UHPLC–MS/MS) method. GHB was extracted from VAMS device by acetonitrile, after a re-hydration step in a temperature-controlled ultrasonic bath at 60°C for 10 min. Chromatographic analysis was carried out on a Kinetex C₁₈ column using 0.1% formic acid in water and acetonitrile as binary gradient mobile phase (from 5 to 95% of acetonitrile from 1 to 2.5 min) at a flow rate of 0.3 ml/min. The VAMS method was fully validated according to current guidelines with satisfactory results in terms of linearity, selectivity, precision, absolute recovery, matrix effect and stability. The linearity was determined from 0.5 to 200 μg/ml and the lower limit of quantitation was 0.5 μg/ml. The novel VAMS–UHPLC–MS/MS method was successfully compared with plasma-based method in a GHB-treated patient as a proof of concept.     

Quasirelativistic valence ab initio calculation of the potential-energy curves for Cd–rare gas atom pairs

The results of large-scale valence ab initio calculations of the potential-energy curves for the ground states and several excited states of Cd–rare gas (RG) van der Waals molecules are reported. In the calculations, Cd²⁰⁺ and RG⁸⁺ cores are simulated by energy-consistent pseudopotentials, which also account for scalar-relativistic effects and spin-orbit interaction within the valence shell. The potential energies of the Cd–RG species in the ΛS coupling scheme have been evaluated by means of ab initio complete-active-space multiconfiguration self-consistent-field (CASSCF)/CAS multireference second-order perturbation theory (CASPT2) calculations with a total 28 valence electrons, but the spin-orbit matrix has been computed in a reduced configuration interaction space restricted to the CASSCF level. Finally, the Ω potential curves are obtained by diagonalization of the modified spin-orbit matrix (its diagonal elements before diagonalization substituted by the corresponding CASPT2 eigenenergies). The calculated potential curves, especially the spectroscopic parameters derived for the ground states and several excited states of the Cd–RG species are presented and discussed in the context of available experimental data. The theoretical results exhibit very good agreement with experiment. Received: 20 April 2000 / Accepted: 1 September 2000 / Published online: 21 December 2000     

Prediction of allergic reaction risk of Shenmai injection based on real-world evidence coupled with UPLC–Q-TOF-MS

The allergic reaction (AR) of Chinese herbal injection (CHI) has become one of the most noticeable focuses of public health in China. However, it still remains a considerable controversy as to whether low-molecular-weight components in CHI have potential sensitization. In this study, the relationship between AR and low-molecular-weight component profile of Shenmai injection was explored by an interdisciplinary technology integrating real-world evidence and ultra-performance liquid chromatography–quadrupole time-of-flight mass spectroscopy (UPLC–Q-TOF-MS). The AR information of hospitalized patients was obtained by comprehensively analyzing real-world evidence from January 2015 to June 2019 at two Chinese hospitals. The UPLC–Q-TOF-MS was exploited to systematically investigate the low-molecular-weight component profile with 50–1500 m/z mass range, and 3725 MS1 peaks were detected. The optimized partial least squares discriminant analysis model was established to map the influence of low-molecular-weight components on AR. The results of this study showed that high levels of organic acids administered intravenously might be a potential risk factor for inducing AR. By using this method, Shenmai injection with high AR risk could be recognized precisely with 100% accuracy before clinical use.     

Matrix solid-phase dispersion coupled with magnetic ionic liquid dispersive liquid–liquid microextraction for the determination of triazine herbicides in oilseeds

A novel method was developed for the determination of six triazine herbicides from oilseeds by matrix solid-phase dispersion combined with magnetic ionic liquid dispersive liquid–liquid microextraction (MSPD-MIL-DLLME), followed by ultrafast liquid chromatography with ultraviolet detection (UFLC-UV). The MIL, 1-butyl-3-methylimidazolium tetrachloroferrate ([C₄mim][FeCl₄]), was used as the microextraction solvent to simplify the extraction procedure by magnetic separation. The effects of several important experimental parameters, including type of dispersant, ratio of sample to dispersant, type and volume of collected elution solvent, type and volume of MIL, were investigated. Using the present method, UFLC-UV gave the limits of detection (LODs) of 1.20–2.72 ng g⁻¹ and the limits of quantification (LOQs) of 3.99–9.06 ng g⁻¹ for triazine herbicides. The recoveries were ranged from 82.9 to 113.7% and the relative standard deviations (RSDs) were equal or lower than 7.7%. The present method is easy-to-use and effective for extraction of triazine herbicides from oilseeds and shows the potentials of practical applications in the treatment of the fatty solid samples.     

A full probabilistic analysis of a randomized kinetic model for reaction–deactivation of hydrogen peroxide decomposition with applications to real data

Journal of Mathematical Chemistry - The classical kinetic equation has been broadly used to describe reaction and deactivation processes in chemistry. The mathematical formulation of this...     

On-column liquid–liquid–liquid microextraction coupled with base stacking as a dual preconcentration method for capillary zone electrophoresis

A simple and efficient dual preconcentration method of on-column liquid–liquid–liquid microextraction (LLLME) coupled with base stacking was developed for capillary zone electrophoresis (CZE) in this paper. Four N-methyl carbamates were used as target compounds to evaluate the enrichment means. The carbamates in sample solutions (donor phase) were extracted into a dodecanol phase immobilized on a porous hollow fiber, hydrolyzed and back extracted into 0.20 μL running buffer (acceptor phase) of 30 mmol/L methylamine hydrochloride (pH 11.6) containing 0.5 mmol/L tetradecyltrimethylammonium bromide inside the hollow fiber, stacked further with 0.5 mol/L NaOH injected at −10 kV for 60 s, and separated by CZE. Analytical parameters affecting the LLLME, base stacking and CZE were investigated, including sample solution volume, pH and temperature, extraction time, stirring rate, buffer component, buffer pH, NaOH concentration, stacking time, etc. The enrichment factors of the carbamates were higher than 1100. The relative standard deviation (RSD) of peak height and limits of detection (LODs) were 4.5–5.5% (n = 6) and 2–4 ng/mL (S/N = 3) for standard solutions, respectively. The proposed method was applied to the analysis of vegetable and fruit samples with the RSD less than 6.0% (n = 3) and LODs of 6–10 ng/g (S/N = 3). The calibration solutions were prepared by diluting the stock solutions with blank sample solutions, and the calibration concentrations ranged from 0.012 to 1.0 μg/mL (r > 0.9951). The analytical results demonstrated that the LLLME coupled with base stacking was a simple, convenient and reliable on-column sample pretreatment method for the analysis of anionic analytes in CZE.     

Vibronic spectra of the allyl radical at 6–8 eV with resonance-enhanced multiphoton ionization technique

The allyl radical was produced in molecular beam by pyrolysis of allyl iodide. The vibronic spectra from ground state to six new electronic states of the allyl radical at 6–8 eV, π →3d^xz, π →3d^xy and π →ns (n=4, 6, 7, 8) were observed firstly with the aid of time-of-flight mass spectros copy and resonance-enhanced multiphoton ionization technique. Vibrational progression ofv ₇(C₃ bend) with gross spacing of about 430 cm⁻¹ was observed inns Rydberg states. The adiabatic ionization potential of the allyl radical was obtained to be (65641 ± 20) cm⁻¹ ((8.138 ± 0.002) eV) by fitting the term values ofns (n=4,6,7,8) Rydberg states with Rydberg formula.