An interface for sensitive analysis of monoamine neurotransmitters by ion-pair chromatography-electrospray ionization-mass spectrometry with continuous online elimination of ion-pair reagents.

A challenge in coupling ion-pair chromatography (IPC) online with electrospray ionization-mass spectrometry (ESI-MS) is that the nonvolatile ion-pair reagent (e.g., alkyl sulfate for amines or tetrabutylammonium for carboxylic acids) in the mobile phase suppresses the ESI-MS signals in the gas phase and their accumulation can clog the MS sampling interface. Consequently, IPC-ESI-MS is conducted either with a volatile ion-pair reagent, which could compromise the analyte separation efficiency, or with a downstream ion-exchange column to rid the ion-pair reagents of the mobile phase. In the latter approach, the limited capacity of ion-exchange columns requires frequent off-line column regeneration, which affects the separation throughput and prohibits long separations from being performed. A dual-valve, dual-ion exchange column interface of IPC-ESI-MS is designed for undisrupted separations and simultaneous column regeneration. Owing to the efficacy in removing the ion-pair reagent, the detection of eluents of monoamine neurotransmitters by an ion trap MS results in the limits of detection of 0.03 µM for dopamine or DA and 0.01 µM for 5-hydroxytryptamine or 5-HT. These values are lower than those obtained with ion trap MS of similar sensitivity when combined with the use of specialized chromatographic columns or sample preconcentration. Excellent reproducibility was attained with repeatedly regenerated ion-exchange columns (RSD = 4-6%) for an extended period of time (RSD < 6% for 6 days). DA and 5-HT in rat straital extracts were analyzed, and our data demonstrate that interferences inherent in the tissues and the ion-pair reagent have been successfully eliminated. This simple interface should be readily amenable to the separation and MS analysis of other types of polar compounds in complex sample media.

The Impact of Urbanization on Tree Growth and Xylem Anatomical Characteristics.

In the context of the intensification of global urbanization, how urbanization (urban heat island effect and air pollution) affects urban tree growth is not fully understood. In this paper, the radial growth and xylem anatomical characteristics of three different tree species (Quercus mongolica, Fraxinus mandshurica, and Pinus sylvestris var. mongolica) in urban and rural areas of Harbin were compared by means of tree-ring anatomy. The results showed that there were significant differences in the growth of both broadleaf trees and conifers between urban and rural areas. The vessel number, cumulative area of vessels, and theoretical hydraulic conductivity of all tree species in rural areas were higher than those in urban areas, indicating that urbanization may have the effect of slowing down growth. However, broadleaf trees in urban areas had higher vessel density and a greater percentage of a conductive area within xylem and theoretical xylem-specific hydraulic conductivity. The thickness of cell walls and cell wall reinforcement index of P. sylvestris var. mongolica were strongly reduced by air pollution, implying that it may be more sensitive to urbanization. Compared to Q. mongolica, F. mandshurica showed less sensitivity to urbanization. Warming and drying climate in Harbin may be an important factor affecting tree growth.

Synthesis of chitosan/TCN nanocomposites with the carbon dioxide assisted phase inversion.

The chitosan (CS)/bis(2-hydroxyethyl)methyl tallow ammonium modified montmorillonite (TCN) nanocomposites are synthesized by the phase inversion procedure via the assistance of carbon dioxide (CO2). The viscosity of CS/formic acid solution is reduced with the incorporation of CO2 owing to the formation of carbamic acid. However, the incorporation of TCN promotes the viscosity of CS solution due to the interaction between TCN and carbamic acid. The morphology of CS/TCN nanocomposites is studied by scanning electron microscopy (SEM), where the surface of the membrane is dense and non-porous. The microstructure of the synthesized CS/TCN composite is further investigated by attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectra, X-ray diffraction (XRD), differential scanning calorimetry (DSC), and transmission electron microscopy (TEM). It is found that the incorporation of TCN without the presence of CO2 disturbs the crystallization of CS. Interestingly, the melting enthalpy of the CS/TCN composite is notably increased with the introduction of CO2, demonstrating that the interaction between the TCN and carbamic acid enhances the formation of CS crystals. XRD and TEM results show that this interaction is able to promote the homogeneous distribution of TCN in the nanoscale with the non-exfoliated form, enhancing the mechanical properties of the synthesized nanocomposites. In particular, the synthesized CS/TCN nanocomposites with the assistance of CO2 present exceptional mechanical properties, where the tensile strength (65.82 MPa) and Young's modulus (3512.48 MPa) are twice as high as that of the CO2 free system.

Synthesis of chitosan/silver nanocomposites by phase inversion with the assistance of carbon dioxide.

Carbon dioxide (CO2) assisted synthesis of water-soluble silver nanoparticle with a narrow particle size distribution is reported here based on the phase-inversion procedure. Bio-derived chitosan (CS) is used to stabilize the metal nanoparticles according to its abundant functional groups. Formic acid is employed as both a solvent (for the polymer) and a reductant for in-situ reducing the silver precursor along with the solvent evaporation. CO2 is utilized to combine with the amino groups of CS, reducing the viscosity of chitosan/formic acid solution and limiting the formation of hydrogen bonds. This promotes the stabilization and reduction efficiency of silver nanoparticles. In particular, 100% of Ag metal nanoparticles with the size of 7.5 ± 2.3 nm is successfully synthesized with the assistance of CO2. Interestingly, the synthesized CS/Ag nanocomposites are water-soluble owing to the formation of carbamate groups. This water-soluble silver nanoparticle presents an exceptional performance in the selective reduction of 4-nitrophenol, where the turnover frequency (TOF = 599 h-1) is even double with respect to the CO2 free system.

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With global climate warming, warming and drying in Northeast China are becoming more and more serious. To understand the effects of drought on the radial growth of Fraxinus mandshurica at different slope positions in Xiaoxing'an Mountains, we analyzed the responses of xylem anatomical characteristics of F. mandshurica to moisture change at different slope positions by wood anatomi-cal method. The results showed that F. mandshurica on the upper and lower slope positions were the same in the changes of xylem anatomical parameters. The abundance of vessels showed a linear distribution, the maximum vessel area and total vessel area showed a logarithmic distribution, while the average vessel area showed a partial normal distribution. There were significant differences in many anatomical parameters among different slope positions. The abundance and area of vessels on the lower slope positions were larger than those on the upper slope positions. Most of the anatomical parameters were significantly positively correlated with daily accumulated temperature, though there were some differences between them. The total vessel area of F. mandshurica on the upper slope positions was positively correlated with the daily mean temperature, while the number and total area of vessels were positively correlated with the relative humidity. The correlation on the upper slope positions was stronger than that on the lower slope positions. The minimum vessel area was negatively correlated with daily accumulated temperature and relative humidity on the upper slope positions, while the total vessel area was positively correlated with relative humidity on lower slope positions. The warming and drying climate would reduce the area and number of vessels in F. mandshurica, but would not affect the distribution of vessels, while the distribution of vessels on the upper and lower slope positions was generally the same. The current climate warming and drying do not limit but promote the radial growth of F. mandshurica.

Long-term effects of post-fire restoration types on nitrogen mineralisation in a Dahurian larch (Larix gmelinii) forest in boreal China.

Fire is an important disturbance agent in Chinese boreal forests but the long-term effects of wildfires on soil nitrogen (N) net mineralisation rates (Rmin) in natural versus human-assisted restorations are not well understood. In this study, we analysed upper (0-10cm) and lower layer (10-20cm) soil samples from natural restoration and afforestation plots in a Dahurian larch (Larix gmelinii) forest in north-eastern China 29years after a mega fire disturbance. Our results showed that the soil inorganic N (NH4+-N and NO3--N) pool of the upper and lower layers of the regenerated plots remained significantly lower than in unburned control plots. This suggests that the effects of a high burn severity fire on soil N availability were still significant almost 30years after the event. Restoration type (natural restoration versus afforestation) also had significant effects on upper layer soil N availability; compared with afforestation, natural restoration was more beneficial for the accumulation of soil inorganic N and the recovery of Rmin after fire disturbance. Specifically, the concentration of inorganic N and the mean Rmin in upper layer soils in the natural restoration plots were approximately 41% greater and 3.6 times greater, respectively, than in the afforestation plots. The differences in soil N availability between the two restoration types were attributed to differences in soil water content (SWC), soil microbial biomass nitrogen (MBN), and the recovery of vegetation after the fire disturbance. Our study demonstrates that natural restoration has proved more successful than afforestation in countering soil N losses in boreal forests in China resulting from a high burn severity fire disturbance.

Performance of a depth encoding PET detector module using light sharing and single-ended readout with SiPMs.

Detectors with depth encoding capability, good energy resolution and good timing resolution are required to develop high performance whole body and total body PET scanners. In this work, an 8 × 8 LYSO array with crystal size of 3 × 3 × 20 mm3 was fabricated by using coupling materials that included 5 mm optical glue, 9 mm triangle ESR reflector and 6 mm rectangle ESR reflector from the top to the bottom in between adjacent crystals in one direction. The LYSO array was single-ended read out by an 8 × 8 SiPM array with one-to-one coupling. Row and column summing circuit was used to read out the SiPM signals. The depth of interaction (DOI) of the detector was measured with the depth dependent light sharing between adjacent crystals while maintaining acceptable energy resolution and timing resolution. The performance of the detector module was evaluated. All crystals can be clearly resolved from the measured flood histogram. An average DOI resolution of 4.62 mm and an average timing resolution of 518 ps are obtained for events with E > 400 keV. The average energy resolution of the detector is 13.5%. This work provides a cost-effective depth encoding detector module that can be used to build high performance whole body and total body PET scanners in the future.