Determination of airborne isocyanates as di-n-butylamine derivatives using liquid chromatography and tandem mass spectrometry

A method for the determination of isocyanates as di-n-butyl amine (DBA) derivatives using tandem mass spectrometry (MS/MS) and electrospray ionisation (ESI) is presented. Multiple-reaction monitoring (MRM) of the protonated molecular ions and corresponding deuterium-labelled d₉-DBA derivatives resulted in selective quantifications with correlation coefficients >0.998 for the DBA derivatives of isocyanic acid (ICA), methyl isocyanate (MIC), ethyl isocyanate (EIC), propyl isocyanate (PIC), phenyl isocyanate (PhI), 1,6-hexamethylene diisocyanate (HDI), 2,4-, 2,6-toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), 4,4′-methylenediphenyl diisocyanate (MDI), 3-ring MDI, 4-ring MDI, HDI-isocyanurate, HDI-diisocyanurate, HDI-biuret and HDI-dibiuret. The instrumental precision for 10 repeated injections of a solution containing 0.1 μg ml⁻¹ of the studied derivatives was <2%. Performing MRM of the product ion [DBA + H]⁺ (m/z = 130) from the protonated molecular ion resulted in the lowest detection limits, down to 10 amol (for TDI). Quantification of concentrations below 10⁻⁶ of the occupational exposure limit (OEL) for TDI during 10 min of air sampling was made possible. In an effort to control the formation of alkali adducts, addition of lithium acetate to the mobile phase and monitoring of lithium adducts was evaluated. Having lithium present in the mobile phase resulted in complete domination of [M + Li]⁺ adducts, but detection limits for the studied compounds were not improved. Different deuterium-labelled derivatives as internal standards were evaluated. (1) DBA derivatives of deuterium-labelled isocyanates (d₄-HDI, d₃-2,4-TDI, d₃-2,6-TDI and d₂-MDI), (2) d₉-DBA derivatives of the corresponding isocyanates and (3) d₁₈-DBA derivatives of the corresponding isocyanates. An increase in number of deuterium in the molecule of the internal standard resulted in an increase in instrumental precision and a decrease in correlation within calibration series.     

Highly enantioselective catalytic acyl-pictet-spengler reactions

The enantioselective cyclization of N-acyliminium ions generated in situ from tryptamine is promoted with high enantioselectivity by a new chiral thiourea catalyst. This represents the first successful system for asymmetric catalysis of the Pictet-Spengler reaction.     

Simultaneous extraction of tetracycline, macrolide and sulfonamide antibiotics from agricultural soils using pressurised liquid extraction, followed by solid-phase extraction and liquid chromatography-tandem mass spectrometry

The veterinary antibacterial agents chlortetracycline (CTC), oxytetracycline (OTC), sulfadiazine (SDZ), erythromycin (ERY) and tylosin (TYL A, B, C and D) were extracted from soil using pressurized liquid extraction (PLE). Citric acid (pH 4.7) and methanol was used as extraction buffer, followed by tandem-solid-phase extraction (SPE) clean-up (SAX + HLB) for all compounds. For quantification two slightly different methods were employed using LC-MS-MS with MRM detection. The soil extraction method was validated using a loamy sand soil and a sandy soil, representing two typical Danish agricultural soils. Recoveries were 50-80% for the tetracyclines (CTC and OTC) and sulfadiazine (SDZ) and 60-100% for the macrolides (TYL and ERY). Limits of detection for the soil extraction method (LOD(soil)) were 0.6-5.6 microg kg(-1) soil for CTC and OTC, 0.9-2.9 microg kg(-1) soil for SDZ and 2.4-5.5 microg kg(-1) soil for TYL A and ERY. Furthermore, the method was applied to field samples taken from two agricultural fields fertilised with liquid manure containing CTC and TYL A. These results showed a decline in the content of antibacterial agents throughout the sampling period of 155 days from 10 to 15 microg CTC kg(-1) soil and 20-55 microg TYL A kg(-1) soil to below or near the LOD(soil) listed above. Finally, the method was applied to barley grains harvested from the fields. None of the antibacterial agents were measured in grain samples, but recoveries for spiked grain samples were similar to soil recoveries.     

Pressure-adjusted continual flow heart-cutting for the high throughput determination of amphetamine-type stimulant drugs in whole blood by fast multidimensional gas chromatography-mass spectrometry

Innovative features and technical improvements in modern bench-top quadrupole gas chromatograph-mass spectrometer (GC-MS) have prepared the way for faster and more cost-effective applications while still maintaining sufficient chromatographic resolution, speed of MS data acquisition and reliability of analytical methodology. In this paper, a short wide-bore capillary column with low film thickness (5 m x 0.32 mm i.d., 0.1 microm) was used a pre-fractionating column and only chosen heart-cuts were transferred to the second chromatographic dimension (15 m x 0.25 mm i.d., 0.25 microm) by means of a pressure-adjusted continual flow type switching device for quantification of five common amphetamine-type stimulant drugs. The instrumental setting used, in combination with carefully optimized operational fast GC and MS parameters, markedly decreased the retention times of the targeted analytes, e.g., amphetamine 0.891 min and methamphetamine 1.037 min, and the total chromatographic runtime (1.700 min), as well as reducing the need for continuous cleaning of the MS ion source and increasing column life compared with conventional GC-MS approaches. The performance of the instrumental configuration and analytical method was evaluated in validation experiments and the method was also applied to authentic samples. The method demonstrates the potential of fast GC-MS in combination with a gas-phase microfluidic Deans switch device for analysing of (semi)volatile compounds, such as amphetamine-type stimulant (ATS) drugs. This should be particularly useful in modern laboratories aiming at cost-efficient analysis as well as the optimum use of available laboratory capacity and instrumentation.     

Ionic-charge dependence of the intermolecular coulombic decay time scale for aqueous ions probed by the core-hole clock

Auger electron spectroscopy combined with theoretical calculations has been applied to investigate the decay of the Ca 2p core hole of aqueous Ca(2+). Beyond the localized two-hole final states on the calcium ion, originating from a normal Auger process, we have further identified the final states delocalized between the calcium ion and its water surroundings and produced by core level intermolecular Coulombic decay (ICD) processes. By applying the core-hole clock method, the time scale of the core level ICD was determined to be 33 ± 1 fs for the 2p core hole of the aqueous Ca(2+). The comparison of this time constant to those associated with the aqueous K(+), Na(+), Mg(2+), and Al(3+) ions reveals differences of 1 and up to 2 orders of magnitude. Such large variations in the characteristic time scales of the core level ICD processes is qualitatively explained by different internal decay mechanisms in different ions as well as by different ion-solvent distances and interactions.     

Electrochemical characteristics of Ce0.8Gd0.2O1.9|La0.6Sr0.4CoO3-δ + Ce0.8Gd0.2O1.9 half-cell

The analysis of the medium temperature half-cell Ce_0.8Gd_0.2O_1.9|70 wt% La_0.6Sr_0.4CoO_3- (LSCO) + 30 wt % Ce_0.8Gd_0.2O_1.9 (CGO) has been made by electrochemical impedance, cyclic voltammetry and chronoamperometry. The shape of complex impedance plots depends on temperature and cathodic polarisation of the electrode. Nyquist (Z, Z-) plots were fitted by equivalent circuit taking into account the electrolyte properties (at very high frequencies), charge transfer process at grain boundaries (at high frequencies), and medium and low frequency O₂ reduction process at the cathode surface and inside the porous cathode material. Two different time constants have been obtained for the cathode process, i.e. for electroreduction of oxygen. It was found that the addition of CGO into the cathode material (LSCO) only somewhat decreases the surface catalytic activity but the noticeably higher low-frequency resistance (i.e. mainly diffusion-like mass transfer resistance R_D) values at lower temperatures have been calculated. It was found that the mainly bulk diffusion-limited process at T773 K deviates toward the kinetically mixed process (diffusion + charge transfer) with increasing temperature.     

Using magnetic core‐shell nanoparticles coated with an ionic liquid dispersion assisted by effervescence powder for the micro‐solid‐phase extraction of four beta blockers from human plasma by ultra high performance liquid chromatography with mass spectrometry detection

In this work, a novel, efficient, and green sorbent, SiO₂@Fe₃O₄ has been created and functionalized with 1‐butyl‐3‐methylimidazolium hexafluorophosphate as an ionic liquid. This sorbent was applied for microextraction of four beta blockers, propranolol, metoprolol, atenolol, and alprenolol with bupivacaine as internal standard from human plasma followed by liquid chromatography with mass spectrometric detection. A mixture of sodium bicarbonate and sodium dihydrogen phosphate was used as an extractant dispersive agent (effervescent power) to enhance the interaction between the magnetic sorbent and analytes. Main affecting parameters on microextraction and elution were optimized. Figures of merit for dispersive solid phase extraction with ionic liquid coated magnetic nanoparticles assisted by effervescent powder were calculated under the optimized conditions. The detection limits for propranolol, metoprolol, atenolol, and alprenolol were found at 0.33, 0.62, 0.03, and 0.44 ng/mL, respectively. For all analytes, good linearity was obtained. Intra‐ (n = 5) and interday (n = 10) precision were both under 6.3% while the preconcentration factors were obtained in the range between 15–18. The extraction efficiencies for each analyte ranged from 75 to 91%. The method was successfully applied for determination of trace amounts of the beta blockers in human plasma samples.     

Cobalt and Iron Stabilized Ketyl,Ketiminyl and Aldiminyl Radical Anions

Carbonyl and iminyl based radical anions are reactive intermediates in a variety of transformations in organic synthesis. Herein, the isolation of ketyl, and more importantly unprecedented ketiminyl and aldiminyl radical anions coordinated to cobalt and iron complexes is presented. Insights into the electronic structure of these unusual metal bound radical anions is provided by X-Ray diffraction analysis, NMR, IR, UV/Vis and Mössbauer spectroscopy, solid and solution state magnetometry, as well as a by a detailed computational analysis. The metal bound radical anions are very reactive and facilitate the activation of intra- and intermolecular C−H bonds.     

Preparation of La0.75Sr0.25MnO3 Nano-Phase Powders and Films from Alkoxide Precursors

The first purely alkoxide-based sol-gel route to nano-phase powders and thin films of perovskite La_0.75Sr_0.25MnO₃ is described. The phase and microstructure evolution on heat treatment of free gel films to form the target nano-phase oxide were investigated by TGA, IR spectroscopy, powder XRD, SEM and TEM-EDS. The xerogel consisted of a hydrated oxo-carbonate, without remaining alkoxo groups or solvent. Heating at 5°C·min^–1 decomposed the carbonate groups and yielded the pure perovskite La_0.75Sr_0.25MnO₃ at 760°C. The cell dimensions were virtually unchanged from the first observation of perovskite at 680°C, to 1000°C, 4 h. The monoclinic cell of La_0.75Sr_0.25MnO₃ obtained at 1000°C, 4 h, had the dimensions a = 5.475(1), b = 5.504(2), c = 7.771(1) Å, = 90.50(2), fitting the literature data quite well. Crack-free, homogenous, 150 nm thick La_0.75Sr_0.25MnO₃ films were prepared by spin-coating Si/SiO₂/TiO₂/Pt and polycrystalline -Al₂O₃ substrates with a 0.6 M alkoxide solution, followed by heating at 5°C·min^–1 to 800°C, 30 min.