An improved power supply for the magnet in a.c. modulated Zeeman atomic absorption spectrometry

This note describes a simple power supply for a magnet to be used in a.c. ZAA spectrometry. The modified sine wave shape of the 50 Hz 10 kG magnetic field allows a 0.5 ms period at zero field to perform the zero field intensity measurement. At lower maximum field strength, the zero field period can be extended.     

Zeeman atomic absorption spectrometry

The shift of atomic spectral lines in a magnetic field (the Zeeman effect) forms the basis for three novel developments in atomic absorption spectrometry: (i) greatly improved background correction; (ii) the use of forward scattering techniques as an analytical tool; (iii) the determination of small gaseous molecules.     

Construction and performance of an a.c. modulated magnet for Zeeman atomic absorption spectroscopy

A Zeeman atomic absorption spectroscopy system has been constructed utilizing a 50 Hz sine wave modulated magnetic field that can be directed either parallel or perpendicular to the optical axis. The amplitude of the magnetic field strength is adjustable up to 10 kG at a maximum power consumption of 0.7 kW.The readout system allows normal atomic absorption as well as d.c. and a.c. Zeeman atomic absorption measurements. Plots of experimental sensitivity vs magnetic field strength and analytical curves are in agreement with theoretical predictions.Experiments in the presence of filter simulated and real background absorbance show that the described Zeeman instrument is capable of correcting background absorption up to two absorbance units.     

Correction for background absorption and stray radiation in a.c. modulated Zeeman atomic absorption spectrometry

Analytical results are presented obtained with Zeeman atomic absorption (ZAA) using a modified sine wave magnetic field. The measurement at zero field strength is lengthened to 0.5 ms for a 50 Hz magnetic field of 10 kG.The a.c. Zeeman system is extended with an additional intensity measurement performed at an intermediate field strength. The three field Zeeman system (3FZAA) permits simultaneous correction for background absorption and stray radiation at the expense of halved analytical sensitivity. The background correction capabilities of ZAA and 3FZAA are the same. However, the 3FZAA signals show increased noise in comparison to ZAA.In the three field system the roll-over problem, inherent in existing Zeeman systems, is shifted to higher concentration and to higher absorbance. The height and the position of the maximum in ZAA and 3FZAA analytical curves do not depend on the amount of background absorption.A method for the extension of analytical curves in AA is presented. Utilizing an a.c. modulated magnetic field any sensitivity between zero and ordinary AA sensitivity can be obtained.     

Theory of Zeeman atomic absorption spectrometry

A theoretical analysis is presented of the signals observed with different systems that employ the Zeeman effect for background correction in analytical atomic absorption spectrometry.Magnetic modulation of the primary source of radiation offers basically the same possibilities as the deuterium background correction system. Correction for wavelength dependent background absorption is possible only when the magnetic field is applied to the absorbing vapour. Similar expressions are obtained for constant or variable magnetic fields directed either perpendicular or parallel to the optical axis. However, mere magnetic modulation of either the source or the atomizer cannot correct for non-absorbed lines.It is demonstrated that simultaneous correction for non-absorbed lines and background absorption can be attained with a variable magnetic field applied to the atomizer, by taking measurements at three discrete, different field strengths.     

Water analysis by Zeeman atomic absorption spectrometry

Summary The determination of trace element concentrations in fresh and marinewaters presents many difficulties because the quantities generally found are below ppb. It is possible to achieve such low detection limits by extraction followed by atomic absorption spectrometry with electrothermal atomization, provided errors due to non-specific absorption are eliminated as completely as possible. The employment of the Zeeman effect gave a mean for effective correction.The techniques selected for the determination of trace metallic elements are based on the analysis of dry residues for fresh waters and on extraction by organic solvents or ion-exchange resins for fresh and marine waters. In the case of brines, some elements are determined directly, making the Zeeman correction and employing a modifier of the matrix.

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Wasseranalyse mit der Zeeman-AAS

Zusammenfassung Die Bestimmung von Elementspuren in Süß- und Meereswasser bietet Schwierigkeiten, da die Konzentrationen unter dem ppb-Bereich liegen. Solche niedrigen Nachweisgrenzen lassen sich durch Extraktion mit nachfolgender AAS mit elektrothermischer Atomisierung erreichen, vorausgesetzt, daß Fehler durch nicht-spezifische Absorption möglichst eliminiert werden. Dazu wurde der Zeeman-Effekt benutzt. Das beschriebene Verfahren beruht auf der Analyse von Trockenrückständen bei Süßwasser bzw. der Extraktion mit organischen Lösungsmitteln oder Ionenaustauschern bei Süß- und Meereswasser. Im Falle von Solen können einige Elemente direkt mit Hilfe von Zeeman-Korrektur und Matrixmodifizierung bestimmt werden.

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Lecture given at the Collogium on the Analysis of Solids by AAS, Wetzlar, October 8–10, 1984     

Stray light effects in Zeeman atomic absorption spectrometry

A transverse Zeeman atomic absorption spectrometer has been modeled using a polychromatic, optical calculus simulation software program. The models were found to be realistic and greatly facilitated the study of the effects of various Zeeman spectrometer parameters and their interactions. The behavior of the Zeeman spectrometer calibration curves, in the presence of three different types of stray light, was modeled. From the initial results, it seems most likely that the major stray light source in real Zeeman experiments is due to polychromaticity of the light source, even when the source profile is relatively narrow in spectral bandwidth.     

Zeeman atomic absorption spectrometry using high frequency modulated light polarization

This paper reports the novel use of Zeeman atomic absorption spectrometry using high frequency modulated light polarization (ZAAS-HFM), its theoretical basis and experimental validation. Due to the high frequency modulation of the analytical and reference signals, the temporal background correction error is reduced below 10⁻⁵ absorbance units. In addition, the use of ZAAS-HFM enables the operator to increase the apparatus transmittance and therefore to reduce the detection limits and to broaden the dynamic range of the analytical curves.     

Precision and detection limits in Zeeman graphite furnace atomic absorption spectrometry

This is the first theoretical study of photometric errors in Zeeman graphite furnace atomic absorption spectrometry with evaluation of their effect on the precision in the traditional method of peak area determination and the pulse restoration method proposed earlier for linearization and expansion of calibration curves. Besides the fraction of non-absorbed radiation, α, and Zeeman sensitivity ratio, R, the theoretical calculations make use of three more parameters, namely the “energy” value, E, the baseline offset compensation time, t_toc, and the integration time, t_int. The theoretical calculations are supported by experimental data on detection limits for a number of elements and on the RSD obtained in Ag and Cd determinations. A comparison of the precision in the case of pulses with dips has shown the pulse restoration method to be superior over the traditional technique. The theoretical results can be used to improve the measurement precision and the detection limits by proper modification of the spectrophotometer and optimization of experimental conditions.     

Correction of characteristic mass in Zeeman graphite furnace atomic absorption spectrometry

A systematic study has been made of the effect of hollow-cathode lamp current and slit width (SW) of the 4100ZL spectrometer on characteristic mass m₀, Zeeman sensitivity ratio R, and roll-over absorbance A_r, for nine elements: Au, Bi, Cd, Co, Cu, Mn, Ni, Pb and Tl. The lamp spectra near the recommended analytical lines have been investigated for these elements. The data obtained have been combined with a theoretical analysis to show that the self-absorption of the analytical lines observed with increasing current and the rise of non-absorbable radiation with increasing SW affect m₀ and the A_r and R parameters differently. It is shown that a separate correction requiring additional narrow-slit measurement of the A_r parameter is necessary to take into account the SW effect on m₀. A separate-correction method built upon this basis offers a substantial improvement of the accuracy of taking into account the SW effect on m₀ compared with the method of combined correction proposed earlier (E.G. Su, A.I. Yuzefovsky, R.G. Michel, J.T. McCaffrey and W. Slavin, Microchem. J., 48 (1993) 278). Exceptions are the Mn and Ni analytical lines, for which the m₀ correction has turned out to be ineffective both in the separate- and combined-correction procedures because of adjacent absorption-sensitive lines passing through the wider slit.     

Determination of copper in sulfide minerals by Zeeman electrothermal atomic absorption spectrometry

A method for the determination of copper in some sulfide minerals (lorandite, realgar, orpiment, marcasite, stibnite, galenite and sphalerite) by Zeeman electrothermal atomic absorption spectrometry is presented. After the dissolution of samples, copper was extracted with sodium diethyldithiocarbamate into different organic solvents (carbon tetrachloride, chloroform and methylisobutyl ketone) at pH 11.0–12.0. The procedure was verified by standard addition. The standard deviation (SD) for 0.5 ng Cu is 0.01 ng, the relative standard deviation ranges from 3.5 to 5.5% and the detection limit of the method, calculated as 3 SD of the blank, was found to be 0.05 μg · g^–1.     

Determination of copper in sulfide minerals by Zeeman electrothermal atomic absorption spectrometry

A method for the determination of copper in some sulfide minerals (lorandite, realgar, orpiment, marcasite, stibnite, galenite and sphalerite) by Zeeman electrothermal atomic absorption spectrometry is presented. After the dissolution of samples, copper was extracted with sodium diethyldithiocarbamate into different organic solvents (carbon tetrachloride, chloroform and methylisobutyl ketone) at pH 11.0–12.0. The procedure was verified by standard addition. The standard deviation (SD) for 0.5 ng Cu is 0.01 ng, the relative standard deviation ranges from 3.5 to 5.5% and the detection limit of the method, calculated as 3 SD of the blank, was found to be 0.05 μg · g^–1. Received: 26 May 1997 / Revised: 10 September 1997 / Accepted: 16 September 1997     

Extension of working range in Zeeman graphite furnace atomic absorption spectrometry by nonlinear calibration with prior correction for stray light

The nonlinear working range of a Perkin-Elmer 4100Zl atomic absorption spectrometer was improved in three steps. Firstly, each absorbance datum within the transient profile was corrected for the presence of stray light by an algorithm originally developed by L'vov and co-workers (Spectrochim. Acta Part B, 47 (1992) 889–895 and 1187–1202), but with the incorporation of the Newton method of successive approximations (Spectrochim. Acta Part B, 49 (1994) 1643–1656. Secondly, a dip correction procedure was performed on temporal signal profiles that exhibited a dip due to rollover. In the final step, an analytically useful working curve was generated by the nonlinear calibration routine of Barnett (Spectrochim. Acta Part B, 39 (1984) 829). Goodness of fit between the resultant calibration curve and the data was measured by the method suggested by Miller-Ihli et al. (Spectrochim. Acta Part B, 39 (1984) 1603) that is based on the sum of squares of the percentage deviation (SSPD) and the root mean square (RMS) percentage deviation. For lead, silver, copper, thallium, and cadmium, the analytical nonlinear working range was increased by as much as one and a half orders of magnitude, without any significant effect on the RMS. For chromium and manganese, no significant improvement in the nonlinear working range was observed, while the RMS improved by 50%. In the case of nickel, neither the working range nor the RMS was improved.     

Effectiveness of linearization of calibration curves in Zeeman graphite furnace atomic absorption spectrometry

A theoretical analysis is made of the effect of analytical line broadening and of non-absorbable radiation in the light source on the shape of concentration curves in Zeeman graphite furnace atomic absorption spectrometry. These results have been used in a systematic study of the effect of spectrometer slit width and hollow-cathode lamp (HCL) current on linearization of calibration graphs for 11 elements: Ag, Au, Bi, Cd, Co, Cu, Fe, Mn, Ni, Pb, and Sb. The effectiveness of linearization throughout the analytical range covered was estimated experimentally on series of 25–30 solutions. Three solutions in each series were used as standards for constructing the calibration graph, the others serving to evaluate the linearization effectiveness. Increasing the slit width and decreasing the HCL current compared to the standard measurement conditions have permitted us to reach a sufficiently high effectiveness of linearization for all the elements studied, with the exception of Ni. The maximum deviation of experimental points from the linear graph under optimum conditions does not exceed 6%. The effect of the Δ parameter used in the computational algorithm on linearization effectiveness is investigated.     

Validation of mercury determination by solid sampling Zeeman atomic absorption spectrometry and a specially designed furnace

Certified reference materials (CRMs) of different origin were used to validate the direct determination of total mercury by solid sampling Zeeman atomic absorption spectrometry (SS-ZAAS) and a specially designed furnace. The temperature program provides only for one step. Atomisation of mercury and pyrolysis of the matrix is performed at a constant temperature in the range of 900–1000 °C. Calibration points achieved by CRMs and aqueous solutions are covered by one calibration line, indicating the absence of matrix effects. Relatively high amounts of chlorine, known for causing problems in mercury determination do not influence analytical results. The excellent accuracy of the method results in a very good agreement with the certified values. The precision of SS-ZAAS measurements in a range from 0.5 to 50 ng Hg does not exceed 3% R.S.D. A limit of quantification of 0.008 μg g⁻¹ Hg was achieved.     

Improved algorithm for linearization of calibration curves in Zeeman graphite furnace atomic absorption spectrometry

A two-parameter model for simulation of concentration curves in Zeeman graphite furnace atomic absorption spectrometry is proposed. The algorithm based on this model can be used for linearization of calibration curves up to the roll-over point. The merits of the algorithm are supported by experimental data obtained for 20 elements under different measurement conditions (light source current and slit width), including the cases where the curvature of the initial calibration curves originates partially from mass-dependent chemical effects and/or non-uniform atom distribution over the furnace cross section. The linearization error does not exceed the random scatter for replicates.     

Use of solid sampling Zeeman atomic absorption spectrometry (SS-ZAAS) for certification purposes

Three methods for the calibration of solid sampling Zeeman atomic absorption spectrometry allowing independent calibration based on gravimetric principles and thus usable for certification purposes are described and intercompared: standard addition to the solid sample, use of synthetic solid matrix matching samples and extrapolation to zero matrix. The first two methods lead to the best results, extrapolation to zero matrix is less suited at high concentrations, but is useful where an accuracy of the order of 10% is acceptable.Presented at the 5th International Colloquium on Solid Sampling with Atomic Spectroscopy, May 18–20, 1992, Geel, Belgium. Paper edited by R.F.M. Herber, Amsterdam     

Determination of boron isotope ratios by Zeeman effect background correction-graphite furnace atomic absorption spectrometry

A new method for the determination of isotopic ratio of boron using Zeeman effect background correction-graphite furnace atomic absorption spectrometry with conventional atomizer and natural-boron hollow cathode source is described. The isotope-shift Zeeman effect at 208.9 nm is utilized for isotopic ratio determination. At a given concentration of total boron, the net absorbance decreases linearly with increasing ¹⁰B/¹¹B ratio. The absorbances are recorded at the field strength of 1.0 T. The isotope ratios measured by the proposed method were in good agreement with the results obtained by inductively coupled plasma-quadruple mass spectrometry or thermal ionization mass spectrometry. The present method is fairly fast and less expensive compared to the above techniques and is quite suitable for plant environments.     

Polarized Zeeman effect atomic absorption spectrophotometry using a flame atomizer

A static magnetic field at 10 kG$\text{\$}\text{?}$was applied to a 10cm laminar flame produced by a premix type burner, and absorptions were observed for the polarized components of the radiation from a hollow cathode lamp. The dynamic range of the measurement was 10⁴–10⁵ for typical elements.The results showed that (1) the optimal conditions for double beam measurement and accurate correction of background absorption are achieved at the same time, (2) even if the flame conditions and the light intensity are changed, the baseline is not shifted, (3) the flame fluctuation noise and the lamp flicker noise are reduced, and (4) background absorption is corrected exactly at the same wavelength as the atomic absorption line.We thus concluded that the feasibility of flame atomic absorption spectrophotometry is much improved with this technique.