Comparison of electrospray ionization and atmospheric pressure chemical ionization techniques in the analysis of the main constituents from Rhodiola rosea extracts by liquid chromatography/mass spectrometry

Rhodiola rosea L. (Golden Root) has been used for a long time as an adaptogen in Chinese traditional medicine and is reported to have many pharmacological properties. A liquid chromatographic (LC) method with mass spectrometric (MS) detection based on selected ion monitoring (SIM) was developed for determining salidroside, sachaliside 1, rosin, 4-methoxycinnamyl-O-beta-glucopyranoside, rosarin, rosavin, cinnamyl-(6'-O-beta-xylopyranosyl)-O-beta-glucopyranoside, 4-methoxy-cinnamyl-(6'-O-alpha-arabinopyranosyl)-O-beta-glucopyranoside, rosiridin and benzyl-O-beta-glucopyranoside from the callus and plant extracts in one chromatographic run. Good linearity over the range 0.5-500 ng ml(-1) for salidroside, 2-2000 ng ml(-1) for rosavin and 2-500 ng ml(-1) for benzyl-O-beta-glucopyranoside was observed. The intra-assay accuracy and precision within quantitation ranges varied between -10.0 and +13.2% and between 0.7 and 9.0%, respectively. Optimization of the ionization process was performed with electrospray and atmospheric pressure chemical ionization techniques using four different additive compositions for eluents in the LC/MS scan mode, using both positive and negative ion modes. The best ionization sensitivity for the compounds studied was obtained with electrospray ionization when using pure water without any additives as the aqueous phase.     

1H NMR and IR spectra of methyl dichloropropanoates and butanoates

Methyl dichloropropanoates and butanoates were synthesized and their ¹H NMR and IR spectra were studied. Comparisons were made with the spectral characteristics of corresponding monochlorocompounds. Special attention was given to the elucidation of the characteristic spectral features associated with particular chlorine substitution patterns. The ¹H NMR of erythro and threo methyl 2,3-dichlorobutanoates were analyzed using a computer program MAOCON, a modified LAOCOON 3 program. In the spectrum of the threo form the order of the chemical shifts of protons on asymmetric carbons seems to be opposite to that reported in earlier literature. Also vicinal coupling constants J₂₃ were found to be greater than those reported earlier.     

On eigenvalues of meet and join matrices associated with incidence functions

Let (P,?,∧) be a locally finite meet semilattice. Let

     

Appearance potentials determined by the electron-impact method as an analytical aid in the evaluation of conformational energies and clarification of ring conformation—I: Appearance potentials of the [M?R]+· ions formed in the primary fragmentation of stereo-isomeric 1,3-dioxans. A direct route to conformational energies

The appearance potentials for the major primary fragmentation ions of three pairs of isomeric methyl-1,3-dioxans were measured. The correlation between the differences in these appearance potentials for each pair and the differences in the standard heats of formation for the corresponding isomer pairs is discussed.     

A few remarks on the simulation and use of crystal field energy level schemes of the rare earth ions

The usefulness of the simulation of the energy level schemes of the trivalent rare earth (R³⁺) ions in the prediction of the properties of the rare earth compounds is demonstrated for a few selected cases emphasizing the connection between different spectroscopic and magnetic properties of the R³⁺ ions. The importance of the calculated energy level schemes in the UV-VUV range in interpreting complicated spectra and designing new phosphors by energy transfer and quantum cutting is described. In the absence of direct measurements, the calculated energy level values can be very useful. The possibilities to interpret the magnetic properties of the R³⁺ (and R²⁺) ions are described by using the wave functions of the energy levels obtained from the energy level simulations. As a fine example, it is shown how the amount of an Eu²⁺ impurity can be obtained from the calculation of the paramagnetic susceptibility as a function of temperature. The problems involved in the simulation of the ⁷F_J crystal field energy level scheme of the Eu³⁺ ion are highlighted by using a comparison between the extensive literature data and calculated level schemes.     

Three-body collisions as a particle formation mechanism in silver nanoparticle synthesis

Silver nanoparticles were prepared in a tubular flow reactor using an evaporation-condensation technique. The size distribution of the particles was measured using standard aerosol instruments and electron microscopy. A comparison with results obtained by a discrete population balance model with molecule-by-molecule resolution suggest that the particles probably nucleate kinetically through a dimerization process instead of a thermodynamic pathway over a free energy barrier, as is typically described by classical nucleation theory. Furthermore, the kinetic rate of dimerization seems to be accompanied by a correction term, associated with the requirement of energy and momentum conservation in molecule-molecule collisions. This energy conservation requires the presence of three-body collisions at the very initial step of particle formation.     

Bounds for ratios of eigenvalues using traces

Let A be an n × n matrix with real eigenvalues λ₁ ? … ? λ_n, and let 1 ? k < l ? n. Bounds involving trA and trA² are introduced for λ_k/λ_l, (λ_k ? λ_l)/(λ_k + λ_l), and {kλ_k + (n ? l + 1)λ_l}²/{kλ²_k + (n ? l + 1)λ²_l}. Also included are conditions for λ_l >; 0 and for λ_k + λ_l > 0.