G. Hermann

Sample transport efficiency with electrothermal vaporization and electrostatic deposition technique in multielement solid sample analysis of plant and cereal materials

Abstract A graphite furnace of the boat-in-tube type as electrothermal vaporizer (ETV) and an electrostatic precipitator were used for determining analyte transport efficiencies and dependencies on plant and cereal matrices, and on carrier elements. All analytical measurements were carried out with coherent forward scattering (CFS) using simultaneous multielement determinations. Transport efficiencies of up to 19% for Cu, 21% for Fe and Mn, and 36% for Pb from the ETV boat to the L’vov platform were obtained for the standard reference materials BCR CRM 281 rye grass, BCR CRM 189 wholemeal flour and NIST SRM 1567 wheat flour and multielement standard solutions containing approximately the same element ratios as certified for the solid samples. The analytical accuracy of the procedure including the ETV process and the electrostatic deposition was tested with Cu, Fe and Pb in BCR CRM 281, Cu, Fe and Mn in BCR CRM 189, and Fe and Mn in NIST SRM 1567 by weighing the solid sample onto the ETV-boat and calibrating against multielement standard solutions dosed into the ETV-boat as well. The analyte addition technique was tested with Cu, Fe and Mn in wholemeal flour. The deviations of the results were below 10% and the relative standard deviations (R.S.D.) values were typically 3–10%. The influence of added potassium and palladium nitrates as physical carriers on the transport efficiencies of Ag, Al, Cd, Cu, Fe, Ni, Pb and Zn standard solutions was investigated with simultaneous multielement determination. Using K and Pd as carriers increased transport efficiencies by factors up to 1.74 in comparison to measurements without an added carrier.

Transport efficiencies and analytical determinations with electrothermal vaporization employing electrostatic precipitation and electrothermal atomic spectroscopy

Abstract Analyte transport efficiencies of solid as well as liquid samples were determined for electrothermal vaporization (ETV). A graphite furnace of the boat-in-tube type was employed for ETV. The generated aerosol was transported by an argon flow via a tubing into an external precipitator and deposited on a L’vov platform with a corona-like discharge. The sample on the secondary platform was analysed with a laboratory-constructed coherent forward scattering multielement spectrometer. For determining the analyte transport efficiencies, the comparative measurements were carried out with standard solutions dosed directly on the platform in the spectrometer furnace. The simultaneously investigated elements were Cu, Fe and Mn in the standard reference material BCR CRM 189 wholemeal flour and in a multielement standard solution containing approximately the same element ratio as certified for the solid sample. ETV boat-to-L’vov platform transport efficiencies of approximately 19% for Cu, 24% for Fe and 19% for Mn were calculated for both solid samples and multielement standard solutions. Cu, Fe and Mn in wholemeal flour were determined simultaneously by calibrating against aqueous multielement standard solutions injected into the boat as well as by the standard addition method. The results agree satisfactorily, the deviations from the certified values are below 10% and the relative standard deviations are typically 5–8%. The limits of detection are 250 pg for Cu (λ=324.8 nm), 230 pg for Fe (λ=248.3 nm) and 90 pg for Mn (λ=279.8 nm), loaded into the ETV boat.

Hyperfine structures and isotopic shifts of the Cu D1 and D2 lines measured by high-resolution laser fluorescence spectroscopy with a collimated atomic beam

Abstract The hyperfine A- and B-factors of the 42S 1 2 , 42P 1 2 and 42P 3 2 states as well as the isotope shift of the related D1 and D2 resonance lines have been measured with high accuracy for copper. High-resolution laser fluorescence spectroscopy and a collimated atomic Cu beam have been employed to reduce Doppler and pressure broadening. The measurements are in good agreement with literature data and improve the accuracy of the 42P 1 2 hyperfine structure considerably, and that of the isotope line shifts by more than one order of magnitude.

Hyperfine structures and level isotope shifts of then2S1/2 (n=7 – 12)- andn2D3/2,5/2 (n=6 – 10)-levels of203,205Tl measured by atomic beam spectroscopy

Applying atomic beam laser spectroscopy, hyperfine constants as well as level isotope shifts of the (6s2ns)2S1/2 levels (n = 7 – 12) and (6s2nd)2D3/2,5/2 levels (n = 6 – 10) have been measured in203Tl and205Tl. Furthermore, some new hyperfine constants and level isotope shifts of the Tl2P1/2,3/2-states are presented together with corrected results of earlier experiments. The hyperfine splittings have been compared with the predictions of the semiempirical theory. For theD-states a relatively poor agreement between these theoretical predictions and experimental results has been found. Using the experimental level isotope shifts and the δ〈r2〉 value from muonic X-ray data, results of single-configuration Dirac-Fock calculations have been tested.

Simultaneous multi-element determination with coherent forward scattering spectrometry employing chromatically corrected polarizers and a fast scanning spectrometer

Abstract A new coherent forward scattering spectrometer for simultaneous multi-element determination on up to 20 atomic lines has been constructed and evaluated. The apparatus consists of a continuum primary source, calcite Glan-Taylor polarizers equipped with a laboratory-designed chromatic correction for the wavelength range 214–766 nm, an electrothermal atomizer with magnet and autosampler and a laboratory-constructed wavelength modulated polychromator with medium resolving power. Light intensities of up to 20 resonance lines in the wavelength range of 214–500 nm are transferred from the focal plane to an array of 20 miniature photomultipliers by optical fiber-bundles. The instrumentation is controlled by a computer. Owing to modular construction the graphite furnace can be exchanged by a flame. Simultaneous multi-element determinations of Ag, Al, Ca, Cd, Co, Cr, Cu, Fe, K, Mn, Na, Ni, Pb, Sr, Tl and Zn are carried out. The received analytical curves cover 1.5–2.5 orders of magnitude per atomic line, which is in the same order as with multi-element measurements with electrothermal atomic absorption spectrometry (ETAAS). Further working range expansions are demonstrated with determining on resonance lines with different strengths. The detection limits for the strongest resonance line of most elements are in the μg l −1 -range and are one order of magnitude higher than those measured with commercially available ETAAS instrumentation when determining four elements simultaneously. The crossed-to-open extinction ratio of the chromatically corrected Glan-Taylor polarizers is determined to approximately 2.5×10 −5 under installed conditions with the graphite furnace and its two windows in between. The spectral transmissions of these polarizers and the optical fiber-bundles are measured with a photometer. It shows a steep decay for wavelengths below 220 nm.

Size and distribution of particles deposited electrostatically onto the platform of a graphite furnace obtained using laser ablation sampling

Abstract Electrostatic particle deposition onto the platform of an ETA graphite furnace was investigated by solid sampling employing laser ablation. The aerosol generated by laser ablation is transported into the furnace by an Ar gas flow. It is piped into the tube through the dosing hole via a capillary. The deposition onto the graphite platform is achieved by impact as well as electrostatically by a discharge. The deposition efficiency was investigated with steel samples, the sample distribution on the graphite platform and the size of the deposited particles was investigated with steel, phosphate rock and plastic samples. Employing electrostatic precipitation, particles with diameters down to about 5 nm are deposited. The efficiency is measured by an additional external precipitator, showing almost quantitative deposition of the introduced particles.

Calculated transmission line structures of a Cu coherent forward scattering resonance monochromator (CFSRM)

Abstract Transmission line structures of a copper coherent forward scattering resonance monochromator (CFSRM) have been calculated. Using a PC with a home-made program, the Hamiltonians of the upper and lower state have been diagonalized including magnetic dipole and electric quadrupole hyperfine interaction and an external magnetic field, without neglections, as for the Zeeman or the Back-Goudsmit limit. By using the resulting transition wavelengths and intensities as well as the Voigt function with its Lorentzian and Gaussian contributions, the line profiles have been calculated. The theoretical results are in good agreement with previous measurements that have been carried out for optimization of the CFSRM in order to suppress interfering Fe emission, which appears in the narrow gap between the two Cu main hyperfine components. The calculations also confirm the non-trivial effects that were found in the measurements. The program, furthermore, supports the calculation of ZAAS absorbances on lines with arbitrary hyperfine and isotopic structure.

Multielement determination on strong and weak lines by coherent forward scattering spectroscopy with continuum sources

Abstract Coherent forward scattering spectroscopy in combination with continuum sources allows simultaneous or sequential multielement determination. Since the brightness of the Xe light source does not depend on the strength of the measured atomic lines, the dynamic range can be strongly expanded by measuring on resonance lines of extremely different strengths. Major constituents can be determined on very weak lines, which are too weak for atomic absorption methods using common line sources. Analytical curves for strong and weak alkali lines are presented as well as curves for the group II elements Ca, Mg and Cd, using the strong singlet and the weak singlet-triplet intercombination lines.

The measurement of stable isotope distribution using Zeeman atomic absorption spectroscopy

Abstract The possibilities of stable isotope analysis using AAS are pointed out. The different isotopic effects occurring in optical spectra are discussed and the influence of the isotopic distribution in a sample on the line profile including broadening effects is analysed. An apparatus, based on the Zeeman scanning technique, is described, which can detect variations in the natural isotopic distribution. Measurements were carried out using the intercombination lines of Hg, Cd and Zn.

Use of an on-axis multipass system to improve the detection limits of coherent forward scattering spectroscopy and flame atomization

Abstract Sequential and simultaneous multielement analysis has been carried out using spectrometry of coherent optical forward scattering (CFS) in combination with a continuum light source and flame atomization. An improvement of the detection limits of CFS devices for simultaneous and sequential multielement analysis could be achieved using a multipass mirror configuration. Two on-axis spherical mirrors effect a multiple reflection of incident light through the flame. Thus the CFS intensity is increased by an extended effective path length. The improvement factors for the detection limits have been found in the range between 2.8 and 6.7 depending on the element to be determined. The experimental results for single element as well as simultaneous multielement analysis obtained with and without the multipass mirror system, are related to the estimated improvement factors.