ABSTRACT
This paper describes an analytical method for the determination of reductive sulphur (S(IV), S(-II)) in glass. The glass sample is dissolved in hydrofluoric/hydrochloric acid mixture and the sulphur is separated via distillation in an apparatus made of polyfluoralkoxyethylene (PFA). The distilled hydrogen sulphide is trapped in buffered boric acid-zinc acetate solution and subsequently determined after conversion to an ethylene blue dye. The range of the method lies within a range of 2-1200mugg(-1) reductive sulphur. The quantification limit for reductive sulphur is 2mugg(-1). Different analysed glass types show either no detectable reductive sulphur or up to 30% of the total sulphur content reductive sulphur. The inter-laboratory standard deviation shown by a round robin test performed is excellent (+/-4mugg(-1); average 59mugg(-1)). Sources of error of the methodology are discussed.
ABSTRACT
The binding state of palladium was studied within the frame of an investigation on the mechanism of analyte fixation during the pyrolysis step in graphite furnace atomic spectrometry. One approach was the determination of the palladium intercalated in the pyrolytic coating of the graphite tube. Due to the low concentrations of intercalated palladium in the pyrolytic coating, precise determination of the shift of certain X-ray lines was chosen. From several investigated valence state sensitive X-ray transitions, the Pd Lbeta2/15 (L3-N4,5) line shift was the one best determinable. The measured line shifts are in the range of -0.14 to 0.71 eV at line widths of 13 eV (fwhm) and a line energy of 3.1729 keV. These very small line shifts were determined by electron probe microanalysis. The detection of the small line shifts was performed with a new method-by evaluation of the change of the intensity in the flanks of the X-ray line. The measurements yielded the following results: inside the pyrolytic graphite, the palladium is distributed inhomogeneously in the form of clusters or islands and in the form of particles on the surface of the pyrolytic graphite. The differentiation between particles and clusters is a very practical one: as long as a particle can be seen in the SEM we talk of particles. Often, however, Pd is detected in an area on the tube or platform surface without detection of a particle. Hence, it can be assumed that the Pd is present in the form of clusters which might even be intercalated in the uppermost graphite layers. The valence state inside these clusters does not appear to be uniform. It can be interpreted as a mixture of Pd with PdO in the center of the clusters or particles (positive peak shift) and of Pd bound to the graphite (strong negative peak shift). On the basis of these observations, a way is proposed to determine how activated Pd atoms in intercalated Pd domains are forming strong covalent bonds to analytes. These bonds are responsible for the analyte fixation of even very volatile analytes.
