P. Hoffmann

Speciation of iron in atmospheric aerosol samples

Abstract The influence of iron in the atmosphere is manifold and a function of its concentration, chemical environment, and solubility. Several analytical methods were applied for the characterization of iron in aerosol samples: for the analysis of solid aerosol samples, instrumental neutron activation analysis, energy- and wavelength-dispersive X-ray fluorescence, Mossbauer spectrometry and electron probe microanalysis were used. For the analysis of the digestion or leaching solutions, total-reflection X-ray fluorescence, atomic absorption spectrometry with flame or graphite furnace atomization and ion chromatography were applied. The bulk iron content of some urban aerosol sample was determined to be about 7% w/w, predominantly occurring as oxides with goethite as the major phase. The major fraction of the investigated aerosol originates from anthropogenic sources. Only 2% of the total iron content is soluble in an aqueous phase.

Chemical characterization of iron in atmospheric aerosols

Abstract The total Fe content, the soluble fractions of Fe(II) and Fe(III), and several species of Fe were determined in various atmospheric aerosol samples by means of atomic absorption spectrometry, ion chromatography and Mossbauer spectrometry.

Transition metals in atmospheric aqueous samples, analytical determination and speciation

SummaryTwo rain water samples were analyzed with respect to the determination of the species which are present at the given conditions. The parameters determined were: pH, Eh, electrolytical conductivity, concentration of anions (SO42−, NO3−, Cl−, NO2−, HCOO−, CH3COO−), of main cations (Na+, K+, NH4+, Mg2+, Ca2+), and of transition metals (V, Cr, Mn, Fe, Co, Cu, Zn). The methods used were filtration and ultrafiltration, voltammetry, sorption on various sorbents and ion chromatography. Furthermore, Eh-pH-diagrams were taken into account and the partition of the species was calculated by means of stability constants. The transition elements species in the atmospheric aqueous solutions are discussed.

Chemical characterization of environmental and industrial particulate samples

The characterization of particles, especially aerosol particles, is of great importance to many scientific fields. A relevant brief overview is given. A rigorous scheme of sampling and in-depth characterization of particulate samples has been developed in the authors’ laboratories and by collaborative groups, including investigations by the following techniques: total reflection X-ray fluorescence spectrometry for quantitative bulk characterization; solid-state speciation by valence band X-ray spectrometry using electron microprobe or Mossbauer spectrometry (only bulk particle characterization possible); scanning electron microscopy and electron probe microanalysis for automatic semiquantitative single particle characterization of particles ≥0.5 µm; transmission electron microscopy for semiquantitative single particle characterization of particles with diameters down to 10 nm; high resolution-scanning electron microscopy, which is also capable of characterizing particles morphologically and qualitatively down to 10 nm in diameter; secondary ion mass spectrometry for the study of trace elemental distributions and isotopic ratios in particles with diameters above 1 µm. It is the aim of this paper to show the advantages and characteristics of this scheme of analysis to match today′s requirements for topochemical methods of analysis. For this purpose a short overview of these methods for particle characterization is also presented.

Characterization of individual atmospheric particles by element mapping in electron probe microanalysis

In this paper procedures for the characterization of individual aerosol particles by element mapping in the electron microprobe are presented. The number, size and qualitative chemical composition of particles is derived from a combination of secondary or backscattered electron images and element distribution maps. Accuracy of the size distribution and reliability of the qualitative analysis procedure were checked with silicate samples. In order to obtain a semi-quantitative estimate of the chemical composition of individual particles the count rates taken from element distribution maps are corrected for matrix and geometric effects using particle ZAF procedures.

Field experimental investigations on the Fe(II)-and Fe(III)-content in cloudwater samples

The Fe(II)/Fe(III)-partition in cloudwater samples collected during two field campaigns is evaluated. It turned out that the simultaneous occurrence of complexing and reducing substances in the atmosphere and the cloud processing increase the solubility of iron compounds present in aerosol particles. A correlation between the concentration of iron(II) in the liquid phase and the intensity of the solar irradiation was observed for most of the cloudwater samples. This could be due to the fact that both the photochemical reduction of the iron(III) complexes and the photochemical reductive dissolution of iron(III)(hydr)oxides are depending on the pH-value. Iron(II) seems to be oxidised back to iron(III) preferably by hydrogen peroxide during the night. Positive correlations were received e.g. between the concentration of dissolved iron and the concentration of oxalate and between the percentage of iron(III) and the concentration of hydrogen peroxide. A negative correlation was found e.g. between the concentration of dissolved iron and the pH-value. The uncertainty of the whole process of sampling and analysis was investigated and the conformity of the results was satisfying considering the sometimes difficult conditions during a field campaign.

Determination of aromatic sulfonic acids in industrial waste water by ion-pair chromatography

A method for the identification and quantification of aromatic sulfonic acids in industrial waste water has been developed. The preparation of the samples comprises a clean-up step and an enrichment step, utilizing i) reversed-phase extraction and ii) ion-pair solid phase extraction. The aromatic sulfonic acids are separated by ion-pair chromatography with diode-array detection. An advantage of the developed ion-pair chromatographic method is the separation of linear alkylbenzenesulfonic acids (LAS), lignosulfonic acids and aromatic sulfonic acids in one chromatographic run. Also described is an optimized clean-up procedure for collected fractions of a preparative chromatographic run to identify monosulfonic acids with GC/MS after methylation. The detection limits for aromatic sulfonic acids in industrial waste waters are at the μg/l level.

The Influence of Oxalate on Fe-Catalyzed S(IV) Oxidation by Oxygen in Aqueous Solution

This study demonstrates that oxalate has a strong inhibiting effect onFe-catalyzed S(IV) oxidation by oxygen in aqueous solution. While thepseudo-first order rate constant of S(IV) oxidation was determined to be1.6 × 103 M-1 s-1 in experimentswithout oxalate, the oxidation of S(IV) was totally inhibited at a molarconcentration ratio of iron:oxalate = 1:5 at an oxalate concentration of 4μM. Under these conditions, the Fe(II)/Fe(III) ratio remained nearlyconstant during the observed reaction time. The determined rate constants wereindependent of the initial oxidation state of iron. However, with increasingconcentrations of oxalate, a longer induction period is observed forexperiments with iron initially in the Fe(II) oxidation state.

In-line determination of U, Pu and Np in process streams by energy-dispersive X-ray fluorescence analysis (EDXRF)

A γ-ray source of ≈300 keV was used in order to excite the fluorescent K-radiation of the heavy elements which is only weakly absorbed in the walls of metal tubes. Thus, uranium can be determined quantitatively in solutions within tubes in the concentration range form 5 mg/l to 100 g/l. The influences of the energy and the activity of the radiation source, the geometrical arrangement, the thickness of the wall and the wall material have been investigated.

Chemical composition of glass beads of the Merovingian period from graveyards in the Black Forest, Germany

White, orange, green and brown glass beads from womens burial places of the Merovingian period were scientifically characterized by x-ray fluorescence analysis, scanning electron microscopy, electron probe microanalysis and x-ray diffraction. In most cases non-destructive procedures were used. By this combination of methods the elemental composition and in some cases the chemical compounds were determined. The elements could be separated into main and minor components of the glass matrix and in those from the colouring compounds. The composition of the glass matrix was determined to be 18 ± 2% Na2O, 67 ± 3% SiO2 and 9 ± 2% CaO. A comparison with literature data showed the similarity of this composition to the composition of glassware of Roman production. Copyright