High-resolution mass spectrometry (HRMS) has become a vital tool for dissolved organic matter (DOM) characterization. The upward trend in HRMS analysis of DOM presents challenges in data comparison and interpretation among laboratories operating instruments with differing performance and user operating conditions. It is therefore essential that the community establishes metric ranges and compositional trends for data comparison with reference samples so that data can be robustly compared among research groups. To this end, four identically prepared DOM samples were each measured by 16 laboratories, using 17 commercially purchased instruments, using positive-ion and negative-ion mode electrospray ionization (ESI) HRMS analyses. The instruments identified~1000 common ions in both negative-and positive-ion modes over a wide range of m/z values and chemical space, as determined by van Krevelen diagrams. Calculated metrics of abundance-weighted average indices (H/C, O/C, aromaticity, and m/z) of the commonly detected ions showed that hydrogen saturation and aromaticity were consistent for each reference sample across the instruments, while average mass and oxygenation were more affected by differences in instrument type and settings. In this paper we present 32 metric values for future benchmarking. The metric values were obtained for the four different parameters from four samples in two ionization modes and can be used in future work to evaluate the performance of HRMS instruments.
Using a facile approach, we successfully made large “defect-free” hyperbranched polystyrene (PSt) chains with uniform subchains between two branching points from the interchain “clicking” of a seesaw-type linear macromonomer [azide∼∼∼alkyne∼∼∼azide] prepared by ATRP with a following conversion of two bromine-ends into two azide-ends, where ∼∼∼ denotes a PSt chain (1.65–31.0 kg/mol). The “click” reaction kinetics monitored by a combination of size exclusion chromatography (SEC) and laser light scattering (LLS) reveals that the degree of self-polycondensation (DP) is related to the reaction time (t) as ln(DP+ 1)/2 = ([A]0
k
AB,0)/β arctan(βt), where [A]0 and k
AB,0 are the initial alkyne concentration and the initial reaction rate between the azide and alkyne groups, respectively; β is a constant and its reciprocal (1/β) represents the time at which k
AB = k
AB,0/2. The results reveal that 1/β is scaled to the macromonomer’s molar concentration ([C]) and molar mass (M) as 1/β ∼ [C]−0.35
M
0.55, indicating that 1/β is governed by the interchain distance and diffusion, respectively. Each hyperbranched sample can be further fractionated into a set of narrowly distributed “defect-free” hyperbranched chains with different molar masses by precipitation. The LLS results show, for the first time, that the root-mean-square radius of gyration (⟨R
g⟩) and hydrodynamic radius (⟨R
h⟩) of “defect-free” hyperbranched polystyrenes in toluene at 25 °C are scaled to the weight-average molar mass (M
w) as ⟨R
g⟩ = 5.53 × 10–2
M
w
0.464 and ⟨R
h⟩ = 2.95 × 10–2
M
w
0.489, respectively, where the exponents are smaller than the predicted 1/2.
Landfill leachate concentrate is a type of refractory organic wastewater with high environmental risk. Identification of refractory components and insights into the molecular transformations of the organics are essential for the development of efficient treatment process. In this report, molecular compositions of dissolved organic matter (DOM) in leachate concentrate, as well as changes after anaerobic/aerobic biodegradation and coagulation with salts, were characterized using electrospray ionization (ESI) coupled with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). DOM in leachate concentrate were more saturated and less oxidized with more nitrogen and sulfur-containing substances (accounting for 50.0%), comparing with natural organic matter in Suwannee River. Selectivity for different classes of organics during biodegradation and coagulation processes was observed. Substances with low oxidation degree (O/C < 0.3) were more reactive during biodegradation process, leading to the formation of highly oxidized molecules (O/C > 0.5). Unsaturated (H/C < 1.0) and oxidized (O/C > 0.4) substances containing carboxyl groups were preferentially removed after coagulation with Al or Fe sulfate. The complementary functions of biodegradation and coagulation in the treatment of DOM in leachate concentrate were verified at the molecular level. Lignin-derived compounds and sulfur-containing substances in leachate concentrate were resistant to biodegradation and coagulation treatments. To treat leachate concentrate more effectively, processes aimed at removal of such DOM should be developed.
Visualizing deep-brain
vasculature and hemodynamics is key to understanding
brain physiology and pathology. Among the various adopted imaging
modalities, multiphoton microscopy (MPM) is well-known for its deep-brain
structural and hemodynamic imaging capability. However, the largest
imaging depth in MPM is limited by signal depletion in the deep brain.
Here we demonstrate that quantum dots are an enabling material for
significantly deeper structural and hemodynamic MPM in mouse brain
in vivo. We characterized both three-photon excitation and emission
parameters for quantum dots: the measured three-photon cross sections
of quantum dots are 4–5 orders of magnitude larger than those
of conventional fluorescent dyes excited at the 1700 nm window, while
the three-photon emission spectrum measured in the circulating blood
in vivo shows a slight red shift and broadening compared with ex vivo
measurement. On the basis of these measured results, we further demonstrate
both structural and hemodynamic three-photon microscopy in the mouse
brain in vivo labeled by quantum dots, at record depths among all
MPM modalities at all demonstrated excitation wavelengths.
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