Method development for the determination of nickel in petroleum using line-source and high-resolution continuum-source graphite furnace atomic absorption spectrometry

Several sample preparation methods have been investigated for the direct determination of nickel in crude oil using graphite furnace atomic absorption spectrometry (GF AAS). Xylene was found unsuitable as solvent because of the poor long-term stability of the solutions and the resulting contamination of the equipment. Isobutyl methyl ketone (IBMK) solutions exhibited better stability, but the sensitivity of the organic nickel salt used for the standard solutions showed a high day-to-day variability. An oil-in-water emulsion using Triton X-100 as surfactant gave the best results. Using high-resolution continuum-source (HR-CS) GF AAS, it could be observed that up to 50% of the nickel in crude oil, most likely low molecular weight nickel porphyrins, were lost already at pyrolysis temperatures >400 °C, whereas the rest of the nickel as well as the nickel standard were stable up to 1300 °C. The nickel absorption at a secondary line at 232.138 nm was recorded simultaneously with that at the primary line at 232.003 nm, expanding the dynamic working range by an order of magnitude. The best characteristic mass obtained was m₀=27 pg and the limit of detection was around 0.07 μg g⁻¹ Ni in oil, based on an emulsion of 2 g oil in 10 ml. The accuracy of the procedure was verified by analyzing the certified reference material (CRM) NIST SRM 1634c, Trace Metals in Residual Fuel Oil.     

Investigation of phosphorus atomization using high-resolution continuum source electrothermal atomic absorption spectrometry

The atomization of phosphorus in electrothermal atomic absorption spectrometry has been investigated using a high-resolution continuum source atomic absorption spectrometer and atomization from a graphite platform as well as from a tantalum boat inserted in a graphite tube. A two-step atomization mechanism is proposed for phosphorus, where the first step is a thermal dissociation, resulting in a fast atomization signal early in the atomization stage, and the second step is a slow release of phosphorus atoms from the graphite tube surface following the adsorption of molecular phosphorus at active sites of the graphite surface. Depending on experimental conditions only one of the mechanisms or both might be active. In the absence of a modifier and with atomization from a graphite or tantalum platform the second mechanism appears to be dominant, whereas in the presence of sodium fluoride as a modifier both mechanisms are observed. Intercalation of phosphorus into the graphite platform in the condensed phase has also been observed; this phosphorus, however, appears to be permanently trapped in the structure of the graphite and does not contribute to the absorption signal.     

Local morphological and dimensional changes of enzyme-degraded cellulose materials measured by atomic force microscopy

A study of the degradation effects of enzyme treatment on the dimensional changes of cellulose aggregate fibrils (CAFs) with dimensions of ∼100,000 × 3,000 × 300 nm from fully bleached kraft fiber was performed. CAFs were incubated with cellulase for up to 32 h. The insoluble CAFs fragments remaining after enzymatic hydrolysis were then subjected to variable relative humidity (RH). Each sample was imaged by an atomic force microscope (AFM) in tapping mode. The images were analyzed to determine the dimensional changes of the insoluble CAFs. Enzymatic hydrolysis continuously depolymerized the CAFs over 32 h, ultimately causing 20% of the CAFs to become soluble. Compared to initial dimensions of the reference CAFs with no enzymatic treatment, the dimensions of the enzyme treated CAFs were generally more responsive to humidity and exhibited an increased frequency of plastic deformations.     

Diffraction of light from weakly modulated silver surfaces

We have investigated the diffraction of light from sinusoidally modulated silver surfaces with grating periods from 4000 to 8000 Å for wavelengths of the visible spectrum. We compare our experiments with theoretical results from a light scattering theory in the first non-vanishing order of the modulation height. This theory includes polarization and the optical constants of the grating material. Good agreement of the theory with the experiments is found for weakly modulated gratings if grating anomalies are avoided.     

Efficient generation of tunable VUV laser radiation below 205 nm by SFM in BBO

Design and performance characteristics of a tunable dye laser system for sum frequency mixing (SFM) in a BBO crystal are presented. The system is composed of two tunable pulsed dye lasers pumped synchronously by the second harmonic of a commercial Nd:YAG laser. The radiation produced by the first dye laser is frequency doubled by second-harmonic generation (SHG) in KDP and subsequently mixed by SFM in BBO with the light of the second dye laser. The interest was focussed on generation of tunable laser radiation below 205 nm with high output power and long-time wavelength stability. High conversion efficiencies enable output energies of 100 J (20 kW) at 196 nm using only moderate Nd:YAG pump energies of 67 mJ. Altogether, a laser system with very good specifications for analytical application in the near VUV spectral region is reported.