Determination of trace elements in zeolites by laser ablation ICP-MS

Laser ablation inductively coupled plasma mass spectrometry using a quadrupole-based mass spectrometer (LA-ICP-QMS) was applied for the analysis of powdered zeolites (microporous aluminosilicates) used for clean-up procedures. For the quantitative determination of trace element concentrations three geological reference materials, granite NIM-G, lujavrite NIM-L and syenite NIM-S, from the National Institute for Metallurgy (South Africa) with a matrix composition corresponding to the zeolites were employed. Both the zeolites and reference materials were fused with a lithium borate mixture to increase the homogeneity and to eliminate mineralogical effects. In order to compare two different approaches for the quantification of analytical results in LA-ICP-MS relative sensitivity coefficients (RSCs) of chemical elements and calibration curves were measured using the geostandards. The experimentally obtained RSCs are in the range of 0.2-6 for all elements of interest. Calibration curves for trace elements were measured without and with Li or Ti as internal standard element. With a few exceptions the regression coefficients of the calibration curves are better than 0.993 with internal standardization. NIM-G granite reference material was employed to evaluate the accuracy of the technique. Therefore, the measured concentrations were corrected with RSCs which were determined using lujavrite reference material NIM-L. This quantification method provided analytical results with deviations of 1-11% from the recommended and proposed values in granite reference material NIM-G, except for Co, Cs, La and Tb. The relative standard deviation (RSD) of the determination of the trace element concentration (n = 5) is about 1% to 6% using Ti as internal standard element. Detection limits of LA-ICP-QMS in the lower microg/g range (from 0.03 microg/g for Lu, Ta and Th to 7.3 microg/g for Cu, with the exception of La) have been achieved for all elements of interest. Under the laser ablation conditions employed (lambda: 266 nm, repetition frequency: 10 Hz, pulse energy: 10 mJ, laser power density: 6 x 10(9) W/cm2) fractionation effects of the determined elements relative to the internal standard element Ti were not observed.     

Synthesis and characterization of the new 22-π aromatic furan-containing macrocycle, “ozaphyrin”

The new 22-π, aromatic “pentaplanar” macrocycle, ozaphyrin ( 6 ), has been synthesized by a McMurry coupling of 5,5′-diformyl-4,4′-dipropyl-2,2′-bipyrrole ( 1 ) with 2,5-bis(5-formyl-4-propyl-2-pyrrolyl)furan ( 5 ). This synthetic pathway to ozaphyrin and its characterization by ¹H nmr spectroscopy, uv-visible spectroscopy, cyclic voltammetry, and X-ray crystallography are described. The structure consists of layers of planar, staggered macrocycles stacked perpendicular to the α-axis. Ozaphyrin crystallizes with four formula units in the monoclinic space group C⁵_2h-P2₁/n in a cell of dimensions a = 10.481(7) Å, b = 17.353(17) Å, c = 18.726(12) Å, and β = 102.84(5)° (108 K). The structure has been refined on F² (5171 unique reflections, 411 variables) to R_w(F_o²) = 0.165. The conventional agreement index R(F) is 0.074 for the 3289 reflections have F_o²>2o(F_o²).     

Results of the ASTM Nuclear Methods intercomparison on NIST apple and peack leaves standard reference materials

The ASTM Task Group on Nuclear Methods of Chemical Analysis (E10.05.12) has conducted a trace element intercomparison among some of its members over the past two years. Eight non-NIST laboratories submitted data using nuclear techniques, with a total of 111 values for the apple leaves and 116 values for the peach leaves, on 46 and 50 elements, respectively. This intercomparison provided a unique opportunity for the analytical laboratories, because the analytical values submitted could be later compared to the NIST certified values. For the seven elements which were certified by NIST and had three or more intercomparison values, the results showed that: 1) 61% of all 56 intercomparison values submitted had results whose stated uncertainty overlapped the uncertainty limits of the NIST certified values, and 2) less than 6% of the intercomparison values had means which fell outside ±20% of the NIST values. In general, the intercomparison values submitted showed excellent agreement with the NIST values. However, many reported uncertainties accompanying intercomparison values appeared overly optimistic.     

Further correlations between fragment ion intensity and critical energy. Unimolecular covalent bond fragmentation

A correlation of fragment ion intensity with critical energy found in the collisional activation spectra of [C₄Ph]⁺˙ ions produced by electron impact can also be found in the unimolecular mass-analysed ion kinetic energy spectra of these ions. The P(E) functions of the unimolecular and collisionally activated ions should differ not only in width but also in structure and therefore, the hypothesis that P(E) functions do not have an important effect on these correlations is tested successfully.     

THE VISUAL PROCESS: PHOTOPHYSICS and PHOTOISOMERIZATION OF MODEL VISUAL PIGMENTS and THE PRIMARY REACTION

Abstract— A systematic comprehensive consideration of the emission spectroscopy, emission lifetimes, transient spectroscopy, as well as quantum yields of fluorescence, triplet occupation and photoisomeriz-ation is given for a wide variety of polyene derivatives including retinyl and longer, as well as shorter chainlength homologs. Absorption spectral properties and the results and significance of theoretical calculations are also included. Chainlength, solvent and temperature effects on state order and photophysical as well as photoisomerization properties are evaluated. The mechanism for the primary light step in vision is considered in light of photophysical and photoisomerization data on model visual pigments and rhodopsin.     

Biosynthesis of anthecotuloide,an irregular sesquiterpene lactone from Anthemis cotula L. (Asteraceae) via a non-farnesyl diphosphate route

Retrobiosynthetic analysis of the allergenic sesquiterpene lactone, anthecotuloide, suggested that this natural product could be formed either by head to head condensation of geranyl diphosphate with dimethylallyl diphosphate, or from farnesyl diphosphate (FPP), the accepted regular sesquiterpene precursor via the rearrangement of a germacranolide precursor. Isotopic labelling of anthecotuloide has now been achieved by feeding [1-(13)C]-glucose, [U-13C6]-glucose and [6,6-(2)H2]-glucose to aseptically grown plantlets of Anthemis cotula(family Asteraceae). Analysis of labelling patterns and absolute 13C abundances using quantitative 13C NMR spectroscopy showed that the isoprene building blocks of this sesquiterpene are formed exclusively via the MEP terpene biosynthetic pathway. This was supported by results from an experiment using [U-13C6]-glucose. A deuterium labelling experiment using [6,6-(2)H2]-glucose supported the original proposal and showed that anthecotuloide is formed from a non FPP precursor. Isotope ratio mass spectrometry suggested that there were two pathways for sesquiterpene biosynthesis in A. cotula.     

Green chemistry and sustainability metrics in the pharmaceutical manufacturing sector

1. Download : Download high-res image (202KB)
2. Download : Download full-size image

     

The infrared spectra and theoretical calculations of frequencies of fac-tricarbonyl octahedral complexes of manganese(I)

The carbonyl stretching frequencies in the infrared spectra of 38 fac-tricarbonyl octahedral complexes of manganese(I) prepared in this laboratory were determined. These complexes may be grouped into three types: (a) neutral complexes of the structure (CO)(3)Mn(P-P)Z where P-P represents depe, dppe, or dppp, and Z represents various anionic functional groups bonded to the manganese; (b) ionic complexes of the structure [(CO)(3)Mn(P-P)Z](+)BF(4)(-) where Z represents various neutral molecules possessing one phosphorous, nitrogen, or oxygen atom coordinated to the manganese; (c) complexes of the structure (CO)(3)Mn(pn)Z where the chelating pn represents 1,1-diphenylphosphino-2,2-dimethylaminoethane, Ph(2)PCH(2)CH(2)NMe(2). All of these complexes show three carbonyl stretching modes (2A' + A"). The effects on the frequencies of these modes induced by both the various Z groups and the various ligands are discussed. Theoretical calculations (B3LYP/6-31G) with optimization of the full molecule make it possible to distinguish between the three stretching modes and to make unambiguous assignments of appropriate symmetry species to each.     

Optimization of an rf-powered magnetron glow discharge for the trace analysis of glasses and ceramics

A radiofrequency (rf) powered planar magnetron glow discharge ion source has been designed and coupled to a double-focusing mass spectrometer. Superposition of the electrical field of the plasma in the cathode dark space and the magnetic field obtained from a ring-shaped magnet located directly behind the sample (cathode) form the electron traps and enhance the sputtering and ionization efficiency of the ion source. In order to establish optimum conditions for the trace analysis of nonconducting materials, mass spectrometric studies have been carried out on the ion signal intensities and energy distributions of analyte and discharge gas ions depending on pressure.