A study of laser ablation and slurry nebulisation sample introduction for the analysis of geochemical materials by inductively coupled plasma spectrometry

Summary The performances of two alternative sample introduction methods for use with Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES) and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) have been evaluated for the analysis of the same sample material. The laser ablation sample introduction system is based on a Nd:YAG laser to which an x-y-z translational sampling head had been added. A study has been made of a number of parameters which affect the performance of the system to find the optimum operating conditions. The slurry introduction system involved aspirating the slurries into the plasma using a de Galan nebuliser and a Scott-type spray chamber arrangement. A study has been made of the parameters which control the production of stable homogeneous slurries. Initial particle size measurements have been carried out on the slurried samples to show how this affects this method of sample introduction. Results are presented for the analysis of a South African reference material rock sample (SARM 5) by ICP-OES with both laser ablation and slurry nebulisation sample introduction and some preliminary results for the analysis by ICP-MS with laser ablation introduction. Semi-quantitative results are obtained for laser ablation ICP-OES as only one matrix matched standard is used. However, the agreement between the results obtained for slurry nebulisation and the certificate value is poor. It is suggested by comparison with previous studies that this may be due to particle size effects. Encouraging results were obtained for the determination of trace elements by laser ablation ICP-MS.     

An efficient closed-shell singles and doubles coupled-cluster method

A reformulated set of equations for the closed-shell singles and doubles coupled-cluster (CCSD) method is presented. A computational cost of n_v⁴n₀²+7n_v³n₀³+1n_v²n₀⁴ for the n⁶ steps is obtained, where n_v is the number of virtual molecular orbitals included in the CCSD procedure, n₀ is the number of doubly occupied molecular orbitals and n=n₀+n_v. Test calculations for the cis and trans isomers of FNNF and planar and pyramidal CH₃⁻ are presented. Equilibrium structures determined with large Gaussian basis sets at the second-order Møller-Plesset (MP2) perturbation level of theory are reported and used for the other electron correlation methods. With the largest one-particle basis set (144 contracted Gaussian functions), the equilibrium geometries of cis- and trans-FNNF agree with experiment. Based on analyses of planar and pyramidal CH₃⁻ wavefunctions and the calculated inversion barrier, it is suggested that the molecular anion may not exist in a planar configuration but that autodetachment of an electron occurs before the transition state is reached. Comparisons of our new CCSD procedure demonstrate that coupled-cluster methods are not significantly more expensive than similar electron correlation techniques.     

Synergetic effect of silver and molybdenum (VI) oxide additives in vanadia catalysts for the selective oxidation of benzene

It has been shown that the selectivity of V₂O₅–MoO₃ catalysts for benzene oxidation to maleic anhydride can be enhanced by small amounts of silver introduced by impregnation with AgNO₃ solution. The effect of Ag₂O additive is synergetic and increases with increasing concentration of MoO₃ up to 28.5 mol %. The best effect was obtained when about 7 Ag atoms were introduced for 1000 (V+Mo) atoms at the surface.

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, V₂O₅–MoO₃ - AgNO₃. Ag₂O MoO₃ 28,5 . %. , 7 Ag 1000 (V+Mo).

     

Study of hydrogen adsorption on iridium catalysts

The influence of dispersity on hydrogen adsorption on Ir black and Ir/C catalysts has been studied. It is shown that supported iridium reduces the heat of hydrogen adsorption as compared to Ir black. With decreasing catalyst dispersity, the amount of weakly bound hydrogen increases, while its adsorption heat decreases on all Ir catalysts.

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Ir- Ir/C-. , Ir-. C , Ir-.

     

Phospholipids of the cotton plant of variety Tashkent-3. II. Structure of the main phospholipid fractions

Summary 1. Individual fractions of phosphatidylcholines, phosphatidylethanolamines, phosphatidylinositols, and the X₂ and X₃ phospholipids have been obtained from the combined phospholipids, freed from carbohydrates, of the seed kernels of the cotton plant of variety Tashkent-3.2. The compositions and position distributions of the fatty acids in the main fractions of phospholipids have been studied.3. The possible molecular composition of the phosphatidylcholines, phosphatidylethanolamines, and phosphatidylinositols have been calculated.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 155–158, March–April, 1976.     

Kinetic isotope effect in trans-alkylation with ethylbenezene

Kinetic isotope effect (KIE) measurements in the trans-alkylation of toluene and benzene with ethylbenzene in hexane in the presence of AlBr₃ at 313 K indicate that deuterium in the toluene methyl group causes a small inverse KIE characteristic for a -complex transiton state. The small direct KIE found for the reaction with C₂D₅C₆H₅ does not agree with a mechanism involving alkyl-and -phenylalkyl cations.

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() - AlBr₃ 313 . , , - C₂D₅C₆H₅ , - -.

     

Investigation of isomerization of n-pentane over supported Pt catalyst modified by adsorbed Bi and Pd

-Al₂O₃-supported Bi–Pt and Pd–Pt bimetallic catalysts were prepared by electrochemical metal adsorption. Isomerization of n-pentane was studied over these catalysts in a pulse reactor. It can be concluded from the results that the properties of these catalysts differ substantially from the base Pt/-Al₂O₃ catalyst. On the modified catalysts conversion and the yield of i-pentane was found to be lower although selectivity was better. The ratio of cracking reactions was also lower than over the base catalyst.It is very probable that the adsorbed bismuth was slowly desorbing from the catalyst surface during the experiments.

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Bi–Pt Pd–Pt -Al₂O₃. -, . , Pt/Al₂O₃. , - , . , . , .

     

Temperature and Oxygen Partial Pressure Dependences of the Surface Tension of Liquid Sn–Ag and Sn–Cu Lead-free Solder Alloys

Temperature dependence of the surface tension of liquid Sn–Ag and Sn–Cu base lead-free solder alloys and oxygen partial pressure dependence of liquid Sn–Ag alloy were evaluated using the experimental data obtained, respectively, by the constrained drop method and the sessile drop method in the previous studies [1, 2]. The temperature dependences of the surface tension have maximum positive values when the mol fraction of Ag and Cu is about 0.7, while those for pure liquid Sn, Ag, and Cu have negative values. The calculated values based on Butler’s equations were found to be in reasonable agreement with those of the experimental data. The oxygen partial pressure dependences of the surface tension of liquid Sn–Ag alloys at 1253 K have a minimum value when the mol fraction of Ag is about 0.9 and the oxygen partial pressure is less than about 10⁻¹³ atm. From this, it is considered that the oxygen adsorption increased by adding Ag to Sn when the mol fraction of Ag is less than 0.9.     

On the electronic states of macrocycles of the extended porphyrin family and their coordination compounds

The electronic absorption spectra of Ni, Zn and Mg hemiporphyrazine derivatives are presented and discussed together with theoretical results obtained by INDO/S computations. The absorption spectra of all the metal derivatives show marked red shifts of the lowest energy absorption bands with respect to those of the metal free hemiporphyrazine. The possible explanation that in metal derivatives low lying excited states with a fully conjugated π electron system are present is supported by theoretical computations.     

Triplet state formation and type II decomposition in the photochemistry of pentanone-2

The concentration dependences of the quantum yields of Norrish type II decomposition from the singlet and triplet states and of the triplet yiel were determined in pentanone-2 photolysis in iso-octane. The results were interpreted by postulating dissociative intersystem crossing of a singlet exciplex as an additional route for the population of the molecular triplet state.

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II -2 . , .