Filtern
Dokumenttyp
Referierte Publikation
- ja (4)
Schlagworte
- Boron carbide (1)
- Gas chromatography (1)
- ICP-OES (1)
- Impaction (1)
- Micro-homogeneity (1)
- Microwave induced plasma (1)
- TXRF (1)
For the determination of main and minor components in silicon-based ceramic powders, a decomposition by a combustion with elemental fluorine and separation of the volatile fluorination products by a carrier-gas distillation with a subsequent detection by quadrupole mass spectrometry is described. The necessity and success of the separation step is demonstrated for the determination of boron as a minor constituent in SiC, where the spectral interferences of silicon on the boron signals are decreased considerably. The method developed is shown to be directly applicable to determination of silicon in Si3N4, SiC, and SiO2. The determination of nitrogen in Si3N4 requires additional effort, to separate nitrogen from the excess of fluorine. For the determination of boron, a complete mobilization of BF3 is assured by the presence of an adequate amount of GeF4. Analysis results obtained with different types of calibration show a precision of 30 g for boron at the milligram-per-gram level and a precision between 0.5 and 2% (m/m) for the main components, silicon and nitrogen. Within these standard deviations, the results agree well with the values expected from the stoichiometry, with the results for silicon and boron obtained by wet chemical decomposition and slurry techniques in combination with ICP-OES and with the results for nitrogen obtained by carrier gas heat extraction.
Mit Nanoporen detektieren elektrochemische Biosensoren einzelne Moleküle, Nanopartikel aus molekular geprägten Polymeren erkennen Proteine und Nukleinsäuren, und Nanostrukturen verstärken die Signale in der Ramanspektroskopie. Kleiner wurden auch die Säulenmaterialien für die Flüssigkeits- chromatographie: Partikeldurchmesser liegen unterhalb von 3 µm, Porendurchmesser im 10-nm- Bereich. Nano ist aber nur ein Thema der Forschung in der analytischen Chemie. Der Trendbericht stellt in diesem Jahr auch Rastersondenmethoden und ihre Kombinationen vor, leistungsstarke Lichtquellen und neue Methoden in der Schwingungsspektroskopie, Alternativen zum induktiv gekoppelten Plasma und Atomabsorptionsspektroskopie in der Routineanalytik sowie Anwendungen in der Chemometrik.
The possibilities of a helium microstrip microwave induced plasma, operated at less than 40 W and less than 250 mL min-1 of gas, as source for optical emission spectrometry (MSP-OES) were studied for the element specific detection of halogenated volatile organic compounds, such as chlorinated and brominated alkanes and arenes, after their separation by capillary gas chromatography (GC). After hyphenation of the GC with MSP-OES with the aid of a heated transfer line, different gas chromatographic parameters, like the carrier gas flow (1.43.3 mL min-1) and the oven temperature (100200), as well as different plasma specific parameters, like the forward power (3040 W) and the plasma gas flow (100200 mL min-1), were optimized. In the next step, rotational and excitation temperatures of microstrip plasma were studied in dependence on analyte concentrations between 1 and 10% v/v in pentane and found to be in the order of 12501650, as measured with OH bands, and 61006900 K, as measured with Fe-lines from ferrocene vapor entered in the plasma gas, respectively. Further, it could be shown that the hyphenated technique GC-MSP-OES can be used for the determination of volatile halogenated organic compounds under the use of an internal standard with recovery rates at the order of 90110% at the 25 mg g-1 level. The absolute limits of detection for volatile halogenated organic compounds, obtained with GC-MSP-OES and the Cl I 837.594 nm, Br I 827.244 nm and C I 247.856 nm, were found to be in the ng-range and the relative detection limits in pentane in the µL L-1 range.
We have studied the micro-homogeneity of boron carbide powders by inductively coupled Plasma optical emission spectrometry (ICP-OES) and total reflection X-ray fluorescence spectrometry (TXRF) using slurry sampling. To get information on the particle size distributions of the powders, the stabilized slurries of boron Carbide powders were nebulized, the aerosols were transported into a Batelle impactor and the droplets were collected on the impactor stages bearing TXRF sample holders. In a first series of measurements, parameters of the impaction like the duration of the impaction and the use of glutinous substance on the sample holders were optimized. The different mass size fractions for industrial boron Carbide powders were determined by weight measurements of the fractions collected on the different stages. The established particle size distributions were in the range of 0.5 to >16 µm and found similar to those determined by laser diffraction reported elsewhere. Analyses of the mass fractions by slurry sampling TXRF showed that Ca, Ti, Cr, Mn, Fe, Ni and Cu within the measurements errors were homogeneously distributed over the mass fractions between 0.5 and 4 µm and that their concentrations agreed with the bulk composition, as determined with ICP-OES subsequent to digestion. However, light underestimates were found at the 5 (Mn) up to 150 µg g-1 (Fe) level. Finally, boron carbide powders were washed out with nitric acid with different concentrations and leaching solutions and the residues were analyzed by ICP-OES and TXRF respectively.
It is shown that up to 60% of the residual trace impurities in the powder studied can be removed by leaching with 34% (v/v) of nitric acid.