Hydraulic high-pressure nebulization sample introduction for direct analysis or on-line matrix separation and trace preconcentration in flame AAS

Summary Only by replacement of the pneumatic nebulization by the new hydraulic high-pressure nebulization (HHPN) in flame AAS 2 to 10 times higher power of detection (depending on the element) can be achieved for the direct trace determination in a saturated tungstate solution. HHP-nebulization leads in general to higher sensitivity and additionally to lower matrix interferences. The HHPN-sample introduction system offers also facilities for a quick on-line matrix separation/trace preconcentration. Detection limits of 0.1 to 1 g/g were achieved for a tungsten matrix (depending on the element).     

Accretion Product Formation from Self‐ and Cross‐Reactions of RO2 Radicals in the Atmosphere

Hydrocarbons are emitted into the Earth's atmosphere in very large quantities by human and biogenic activities. Their atmospheric oxidation processes almost exclusively yield RO₂ radicals as reactive intermediates whose atmospheric fate is not yet fully unraveled. Herein, we show that gas‐phase reactions of two RO₂ radicals produce accretion products composed of the carbon backbone of both reactants. The rates for accretion product formation are very high for RO₂ radicals bearing functional groups, competing with those of the corresponding reactions with NO and HO₂. This pathway, which has not yet been considered in the modelling of atmospheric processes, can be important, or even dominant, for the fate of RO₂ radicals in all areas of the atmosphere. Moreover, the vapor pressure of the formed accretion products can be remarkably low, characterizing them as an effective source for the secondary organic aerosol.     

Beam-injection flame-furnace atomic-absorption spectrometry (BIFF–AAS) with low-pressure sample-jet generation

Flame-furnace AAS (FF-AAS) comprises two individual, recently developed FAAS techniques remarkable for their high power of detection and the small amounts of sample required. One of these techniques is beam-injection flame-furnace AAS (BIFF-AAS), whereby the sample is introduced into a flame-heated atomization cell as a high-speed liquid jet. For the first time this sample-introduction beam has been generated at low pressure by use of a peristaltic pump and a special micro channel smooth jet nozzle developed for this application. Compared with standard FAAS a 7- to 17-fold improvement in the power of detection was obtained for six elements (Ag, Cd, Hg, Pb, Se, and Zn). The relative standard deviation (N=15) was between 0.7% and 3.4%. Sample volumes between 10 microL and 1 mL have been investigated. The applicability of the peristaltic pump for beam generation enables an optimum sampling mode for a variety of analytical tasks (continuous sample uptake, manual or automated, or different flow-injection modes). The method can also be regarded as a simple, effective interface between FIA techniques and flame AAS.     

Spektroskopische Untersuchungen an XCH2(CH3)2SiF-Verbindungen

Mössbauer-spectrometric and Catalytic Investigations of the System Pt? Sn? η-Al₂O₃ Tin compounds on an Al₂O₃-carrier exhibit interactions with the carrier, their chemical properties are different from those of the carrier-free compounds. In reduced Pt? Sn? Al₂O₃ catalysts of different preparation there are different interactions between platinum and tin. Impregnation of the carrier with platinum-tin complexes gives vicinal locations of both compounds in socalled Pt? Sn ensembles. The modification of the electronic properties of a part of the platinum by tin in Pt? Sn? Al₂O₃ catalysts causes a decrease of the adsorption of hydrogen and of the activity in the dehydrogenation of cyclohexane, and an increase of the activity of dehydrocyclization of n-heptane.     

Zur reaktion von iminodithiocarbonaten mit carbonsäuren I: Synthese des modellpeptid-derivates Z(L)Ala(L/D)Phe(L)ValOMe

The tripeptide derivative Z(L)Ala(L/D)Phe(L)ValOMe was obtained in 40% yield by reacting (CH₃S)₂CN(L)CH[CH(CH₃)₂]COOCH₃ with the dipeptide derivative Z(L)Ala(L)PheOH and ZnCl₂ at 110°C. The product obtained by bulk condensation contained 9 %, the product obtained utilizing ethylene carbonate as solvent contained 10 % of the diastereomer Z(L)la(D)Phe(L)ValOMe. Separation of diastereomers was achieved by HPLC on a silicagel column.     

Cadmium and lead determination in foods by beam injection flame furnace atomic absorption spectrometry after ultrasound-assisted sample preparation

A simple method for cadmium and lead determination in foods by beam injection flame furnace atomic absorption spectrometry (BIFF-AAS) was proposed. Food slurries were prepared by transferring an exact amount of cryogenic-ground homogenized material (50-100 mg) to centrifuge tubes, followed by addition of 5 ml (up to 2.8 mol l⁻¹) nitric acid solution and sonication in an ultrasonic bath during 5-10 min. Thereafter, slurries were diluted with water to 10 ml, centrifuged during 5 min at 5400 rpm and 400 μl aliquot of the supernatant was analyzed by BIFF-AAS. The detection limits based on peak height measurements were 0.03 μg g⁻¹ Cd and 1.6 μg g⁻¹ Pb for 2% (m/v) slurry (200 mg/10 ml). For method validation, the certified reference materials Pig Kidney (BCR 186) and Rice Flour (NIES 10) were used. Quantitative cadmium and lead recoveries were obtained and no statistical differences were found at 95% level by applying the t-test.     

Investigations on the sorption of metal chelates on activated carbon

The mechanism of the adsorption of chelates on activated carbon is discussed. The models used are amino acids and their nickel complexes. It was confirmed that, in general, sorption is quantitative when the chelate contains systems of π-electrons in the molecule and when the centres for binding on carbon and those for the metal ions are spatially separated so that their orbitals do not have a substantial influence. Other factors, e.g., sulphur atoms in the molecule, the length of the chain, and the existence of hydrophobic or hydrophilic groups in the molecule, must also be considered. The sorption of the amino acids was followed spectrophotometrically and that of the nickel complexes by flame a.a.s.     

In-situ and ex-situ examination of the early stages of chemical vapor deposition

A cold working steel was coated both with high temperature CVD (TiN) and moderate temperature CVD (Ti[C,N]). AES depth profiles show a significant difference at the interface, where a thin oxide layer remains detectable at deposition temperatures of 750 °C. It could be shown that an impedance signal at a frequency of 13 MHz is well suited to detect the early stages of the growth of a CVD coating. Received: 15 July 1997 / Revised: 5 February 1998 / Accepted: 9 February 1998