Rainer Wennrich

Size separation of silica nanospheres by means of capillary zone electrophoresis

The electrophoretic mobility of silica nanospheres was shown to be a function of separation conditions such as pH and phosphate concentration of a carrier electrolyte. The separation selectivity can be controlled by the separation conditions and optimised depending on the sample composition. The effects of pH and phosphate concentration of buffer solutions on the nanosphere electrophoretic mobility are explained using the Overbeek-Booth electrokinetic theory taking into account both electrophoretic retardation and the relaxation effect.

A hyphenated flow-through analytical system for the study of the mobility and fractionation of trace and major elements in environmental solid samples.

A flow-through hyphenated analytical method has been tested that enables not only the accelerated and efficient fractionation of trace elements (TE) species in environmental solids to be achieved but allows real-time studies on the leaching process to be made. Rotating coiled columns (RCC), earlier used mainly in countercurrent chromatography, have been successfully applied to the dynamic fractionation of heavy metals in soil, sediment, and sludge samples. A ground solid sample (about 0.5 g) was retained in a PTFE rotating column as the stationary phase whereas different aqueous eluents, chosen according to recent data on the selectivity of leachants, were continuously pumped through. Elements were determined in the effluent on-line by inductively coupled plasma atomic emission spectrometry (ICP-AES). Since the flow rates used in the RCC are in good agreement with those needed for cross-flow nebulization in the ICP-AES spectrometer, both devices were coupled directly without any additional interface systems. Simultaneous investigation of the elution profiles of trace and major elements has made it possible to study the elements association in separated fractions and hence to prove the efficacy of extractants and their selectivity toward targeted mineralogical phases of samples. The close association of heavy metals with Mn oxides in the sediment and sludge samples was confirmed. The time-resolved dissolution of different organic complexes of metals was observed for the sediment sample. It was found that in sediment and sludge samples the dynamics of iron release under the action of Tamms reagent is somewhat different from that of aluminium. In addition, the proposed method can also be applied to develop effective leaching schemes and in the analysis of environmental solids for risk assessment of their contaminants addressed to water quality and bioavailability.

Mechanisms of the action of platinum metal modifiers in electrothermal atomic absorption spectrometry: aims and existing approaches

Abstract The characteristics of As, Se and In in pure solutions in the presence of pre-reduced Pd, Rh, Ru, Pt and Ir modifiers in the transverse heated graphite atomizer (THGA) for electrothermal atomic absorption spectrometry are studied. Main attention is given to the influence of a wide range of modifier masses to sensitivity and shape of the absorption signals. Over-stabilization of As and In was observed in the presence of moderate amounts of the Pt modifier. Over-stabilization of As begins in the presence of approximately 2 μg of Rh and the addition of 25 μg of this modifier result in almost 3-fold suppression in the integrated absorbance. More than 2-fold suppression was also observed for the In absorption signals in the presence of 25 μg of Ru modifier. Modern knowledge of mechanisms on the action of platinum metal modifiers can neither predict, nor explain these element-specific interactions. Clear correlation between physical properties of the modifiers and analytes, and the data obtained could not be recognized as well. This significant contribution to chemical processes to stabilization of analytes during pyrolysis stage and their subsequent atomization. Some modern approaches concerning mechanisms of the action of platinum group metal modifiers are critically discussed and some trends are underlined.

Low-temperature transformations of sodium sulfate and sodium selenite in the presence of pre-reduced palladium modifier in graphite furnaces for electrothermal atomic absorption spectrometry

Abstract The low-temperature interaction (up to 550°C) of a pre-reduced palladium modifier with sodium sulfate and sodium selenite on the pyrolytic graphite platform was studied using X-ray photoelectron spectroscopy (XPS) and electron microprobe analysis. The equipment applied allowed the introduction of samples heated in an argon flow into the analytical chamber of the XPS spectrometer without contact with the air. Electron microprobe analysis showed that palladium and sulfur preferably occupy different areas on the platform surface. On the contrary, selenium from sodium selenite tends to occupy areas of the graphite surface covered with palladium. The most probable reason for this is the chemisorption of selenium (IV) on the palladium surface at the drying stage. No changes in the XPS spectra of metallic Pd and S6+ were observed when Na2SO4 and Pd were heated together on the graphite platform in the range 100–550°C. The reduction of sodium selenite on the graphite surface already starts during drying. Pre-reduced palladium intensifies this process. The rate of the reduction is proportional to the amount of palladium, and in the presence of palladium at an atomic ratio of Pd/Se=7.5, the transformation of Se4+ into Se0 completes at 250°C.

Spectral interferences in graphite furnace Zeeman effect atomic absorption spectrometry

Abstract Atomic line and molecular band tables were surveyed to select elements and stable diatomic molecules which could potentially cause spectral interferences in inverse Zeeman effect corrected atomic absorption spectrometry. It was found that the 328.1 nm silver line is overcorrected by an interference from rhodium. Background overcorrection caused by molecules was observed at the 279.5 nm manganese line (interference from AlBr, InBr), the 283.3 nm lead line (interference from AlBr, InBr, BaO), the 286.3 nm tin line (interference from InBr, BaO, MgBr), the 267.6 nm gold line (interference from BaO) and the 217.0 nm lead line (interference from AlO). The overcorrection errors could be avoided by using atomization temperatures below 2000°C.

Investigation of phosphorus release from different compounds in electrothermal vaporization inductively coupled plasma atomic emission spectrometry in the absence and presence of modifiers and its application to plant analysis

Abstract Inductively coupled plasma atomic emission spectrometry (ICP-AES) combined with electrothermal vaporization (ETV) was applied to the determination of phosphates in aqueous solutions. The sensitivity for phosphorus was found to depend on the cations in the sample. To understanding this phenomenon the thermal behavior of H 3 PO 4 , (NH 4 ) 2 HPO 4 and KH 2 PO 4 was studied. There were significant differences in the thermal release of phosphorus from these compounds. To explain these phenomena, different reaction mechanisms were calculated using thermodynamic data. La(NO 3 ) 3 and Pd(NO 3 ) 2 were successfully applied as modifiers for the stabilization of phosphates during the thermal pre-treatment step and to establish an uniform thermal behavior. The application of Pd(NO 3 ) 2 as modifier led to uniformity in the thermal behavior and to stabilization of different phosphates tested. This resulted in a good correspondence between the certified and the measured concentrations of total phosphorus in decomposed plant reference materials. The stabilization of using La(NO 3 ) 3 modifier bases on the formation of thermally stable LaPO 4 . This explanation has been supported by comparing the experimental results with thermodynamic calculations considering different reactions for the thermal decomposition of the phosphate. Unfortunately, there are no thermodynamic data for palladium phosphates and phosphides available.

Efficiency of Pt and Ir modifiers for the simultaneous determination of As, Se and In in a sodium sulphate matrix by electrothermal atomic absorption spectrometry.

The effect of pre-reduced Pt and Ir modifiers towards simultaneous determination of As, Se and In in a sodium sulphate matrix was investigated. In spite of application of very isothermal THGA atomizer, negative influence of the matrix is pronounced. The efficiency of iridium modifier is somewhat higher than that of platinum modifier. However compared to palladium modifier both are significantly less effective in sulphate media. Taking into account our previous data, effectiveness of platinum group metal (PGM) modifiers in the determination of As, Se and In in the presence of sodium sulphate increases in the order Ru<Rh approximately Pt<Ir<Pd. This order is opposite to the data on enthalpy of formation of PGM sulphides. This supports our hypothesis that effectiveness of PGM modifiers in the presence of sulphate matrix is determined mainly by stability of the corresponding sulphides. Efforts to enhance the effectiveness of Pt modifier mixing it with small (10-20%) amounts of Pd, Rh or Ir were not successful. Although mixture containing equal amounts of Pd, Pt, Rh and Ru is relatively effective, pure pre-reduced Pd is the best modifier for the simultaneous determination of As, Se and In in a sulphate media.