Optimization of thermostated electrodeless discharge lamps for analytical atomic spectrometry

Thermostated and unthermostated electrodeless discharge lamps (EDL's) operated at 2450 MHz with either an A-antenna or a $\text{3}\text{4}$-wavelength Broida cavity have been critically studied with respect to the effect of type and pressure of fill gas, lamp temperature, microwave power and the form of element and/or compound within the lamp, upon the source radiant output, atomic absorption and atomic fluorescence signals of Zn-213·8 nm, Pb-283·3 nm, Mn-279·5 nm, Hg-253·7 nm and Tl-377·6 nm. Temperature control of electrodeless discharge lamps eliminates most of the problems which have previously plagued their operation. Also as a result of these studies, certain misconcepts in the operation and characteristics of electrodeless discharge lamps have been clarified; e.g., the ‘skin effect’ is present in many electrodeless discharge lamps, but all lamps also exhibit a homogeneous glow discharge; at high microwave powers and/or at high lamp temperatures, spectral lines apparently exhibit little self-absorption and self-reversal; and most important, control of lamp temperature is the most critical parameter controlling spectral output because atomization within the lamps is predominantly thermal in origin. Also, contrary to the conclusions reached by some workers evaluating the analytical usefulness of atomic fluorescence flame spectrometry, it is shown that detection limits one-to-three orders of magnitude lower result when thermostated EDL's are used in atomic fluorescence spectrometry with C₂H₂-air flames.     

Some observations on small-size electrodeless discharge lamps for strontium used for Zeeman scanning of absorption line profiles in flames

Microwave-excited electrodeless discharge lamps (EDL) for Sr were produced and a technique was developed for stabilizing the microwave power. Some characteristics of the EDL were investigated. The lamps were compared with a normal (= non-boosted) commercial hollow cathode lamp (HCL).Half-intensity widths of the Sr-line at 4607.33 Å were determined by interferometry for EDL and HCL sources under various operating conditions. Moreover, with both sources peak absorption measurements were carried out in a flame with Sr vapor; the results obtained by either technique were partially mutually consistent. Selected samples of EDL gave half-intensity widths of about 7–10 mÅ, independent of microwave power.The line width of the HCL increased from about 7 to 20 mÅ with increasing current up to 26 mÅ (= maximum rating). The radiance of the EDL's (at 50 W) was about the same as that of the HCL, when the latter was operated at 10 mA to give a comparable half-intensity width of 10 mÅ. At maximum microwave power the radiance of the EDL appeared to be 15–20 % of that of the HCL at maximum current, but the EDL line width remains only 7–10 mÅ, whereas that of the HCL line is about 20 mÅ and the HCL line is heavily self-reversed. EDL's with radiance values 10–100 × higher than that of the HCL at 25 mA were also produced; the high radiance value is obtained by increasing the Sr content in the EDL drastically. The profile of the EDL line has then a width of about 60 mÅ and the line is heavily self-reversed. Some tentative results on stability and life of the EDL's are reported.     

Evaluation of new high-frequency discharge lamps for atomic absorption and atomic fluorescence spectrometry of cadmium,lead and zinc

High-frequency discharge lamps with a hollow electrode are successfully utilized as the spectral line sources for atomic absorption and atomic fluorescence spectrometry of cadmium, lead and zinc. The sensitivities for atomic absorption spectrometry are superior to those obtained with commercially available hollow-cathode lamps by factors of 1.5 (Cd), 1.4 (Pb) and l.6 (Zn). Detection limits for non-dispersive atomic fluorescence spectrometry with graphite furnace atomization are 1 × 10^-13 g (Cd), 3 × 10^-11 g (Pb) and 2 × 10^-13 g (Zn). The linear analytical range covers over four (Cd, Zn) and three (Pb) decades of concentration above the detection limits.     

The preparation and operation of electrodeless discharge lamps—a critical review

In this paper the literature on electrodeless discharge lamps (EDLs) is reviewed. Several aspects of preparation and operation of EDLs are critically discussed. Attention is also paid to multi-element EDLs and comparisons of EDL's with other light sources. The authors feel that the present situation must be characterized by the conclusion that really concrete and general conclusions cannot be drawn from the literature.     

Atomic line profile measurements on hollow-cathode and electrodeless discharge lamps using a high-resolution echelle monochromator

Commercial r.f.-excited electrodeless discharge lamps (EDLs) and hollow-cathode lamps (HCLs) of the elements As, Bi, Cd, Sb, Se, Sn, Te and Zn were studied using a 2.54-m scanning echelle monochromator. The variation of the widths of the resonance lines from these lamps was investigated for a range of power and current levels. In general, the tendency to self-absorption and self-reversal is greater for the more volatile elements, although the strong self-reversal of the Pb 217.0 nm line from a HCl is an exception. EDLs for the less volatile elements, which are incorporated as iodides, show relatively little variation in line width except at the highest powers.The extent of the overlap between the Bi and I atomic lines at 206.2 nm is demonstrated and, for As, a hyperfine structure splitting constant (A-value) of 0.016 cm⁻¹ was determined for the 5s⁴P energy level.     

Experimental Parameters Affecting the Intensity of Cadmium Electrodeless Discharge Lamps

Abstract

Several experimental parameters have been found to affect the intensity of microwave excited electrodeless discharge emission at the cadmium resonance line (228.8 nm.). A thorough study of the effect of pressure of the fill gas, microwave power applied to the tube; and weight of Cd introduced into the tube has been accomplished. Direct comparisons of Cd resonance emission for the cases of He, Ne, Ar and air fill gases are presented. From these studies preductions of optimum conditions for construction and operation of Cd electrodeless discharge lamps may be made.     

Furnace atomization plasma emission spectrometry with He/Ar mixed gas plasmas

The influence of plasma gas composition on the operating and analytical characteristics of a furnace atomization plasma emission source (FAPES) is presented. He I and Ar I excitation temperatures increase 30% in the mixed gas plasmas whereas argon ion excitation temperatures decrease from 33 000 K to 26 000 K in the presence of He. Collisional exchange of internal energy between excited states of Ar and He accounts for these changes. Average analyte ionization temperatures (for Cr, Mn, Mg, Co, Fe, Cd and Zn), derived from the relative emission intensities of their ionic and atomic lines in a 40-MHz 50-W plasma, increase from 5270 K to 6740 K with the addition of Ar to He. Ionic line intensities increase from 10-fold (Mn) to 40-fold (Cd, Zn) with addition of Ar to the plasma while atomic line intensities increase only twofold. Limits of detection remain substantially unaltered for atomic transitions due to increased noise but are improved twofold (Cd) to 24-fold (Mn) for ionic transitions. The analytical advantages and disadvantages of mixed gas plasmas are discussed. The Ne I excitation temperature at 40 MHz and 50 W was determined to be 4330±80 K.     

Study of ionic-to-atomic line intensity ratios for two axial viewing-based inductively coupled plasma atomic emission spectrometers

Using two axially-viewed inductively coupled plasma (ICP) systems that exhibited different behaviors to matrix effects, the sensitivity of the Mg II 280.270 nm/ Mg I 285.213 nm line intensity ratio to the ICP operating conditions and to matrix effects was compared to that observed for alternative ionic-to-atomic line intensity ratios such as the Cd II 226.502 nm/Cd I 228.802 nm, Cr II 267.716 nm/Cr I 357.868 nm, Ni II 231.604 nm/Ni I 232.138 nm, Pb II 220.353 nm/Pb I 217.000 nm, and Zn II 206.200 nm/Zn I 213.857 nm ratios. Both robust and non-robust conditions were used. Some lines behaved differently, in particular the Mg I and Cr I lines, not only as a function of the matrix, but also as a function of the ICP system. The Mg II/Mg I ratio was found to remain a good compromise to follow changes in plasma conditions. The use of several ionic-to-atomic line ratios confirmed that axial viewing leads to matrix effects that are particularly sensitive for atomic lines. The effects cannot be totally suppressed, even under robust conditions, and regardless of the ICP system. An alternative to minimize matrix effects was the use of a buffer such as Cs at 10 g l⁻¹.     

Some considerations on spectral line profiles of microwave-excited electrodeless discharge lamps

The problems of line broadening in microwave-excited electrodeless discharge lamps for the more volatile elements, P, S, I, Se, Zn, Cd and Hg are discussed in relation to their use in atomic-absorption and fluorescence spectrometry. Both theoretical and practical implications are considered.     

Evaluation of the analytical capabilities of frequency modulated sources in multielement non-dispersive flame atomic fluorescence spectrometry

Frequency modulated sources of Cd and Zn are used to produce modulated atomic fluorescence signals (at two different frequencies) in a non-dispersive flame atomic fluorescence spectrometer. To reduce the flame background level, a chlorine filter, a separated air—acetylene flame, and a solar blind photomultiplier are used. Even so, there is shown experimentally and theoretically to be a multiplex disadvantage, as compared to the conventional single slit scanning dispersive spectrometer, as a result of the flame background photon noise and an additional multiplex disadvantage at high concentrations of an interference, e.g. in the measurement of Zn (213.9 nm), Cd (228.8nm) results in a reduced S/N for Zn when the Cd signal level becomes comparable with the flame background signal level. Little future for multiplexed techniques in atomic flame spectrometry in the u.v.- Visible is predicted.     

High frequency excitation of vapours produced by hollow cathode sputtering

Using a hollow cathode discharge for producing a suitable atomic vapour, the spectral lines of elements were excited by a high frequency discharge of 2450 MHz. These lamps were used as primary light sources for atomic absorption spectroscopy and were compared with conventional hollow cathode lamps. Higher intensity of radiation as well as higher sensitivity was obtained with the high frequency discharge. The interaction of the microwave field with the hollow cathode discharge limits the ultimate intensity. The stability of radiation from these sources is good. Measurements of line halfwidths indicate gas temperatures of approximately 500°K for both the high frequency and conventional hollow cathode discharges.     

Performance and application of controlled temperature-gradient lamps in atomic absorption spectrometry

An improved design of controlled temperature-gradient lamp (CTGL) is suitable for arsenic, cadmium, phosphorus, potassium, rubidium, selenium, sodium, sulphur and zinc. Intensity and linewidth measurements indicate that the CTGL is significantly more intense than an electrodeless discharge lamp (EDL) at the same linewidth. CTGL's also compare favourably with EDL's when used as light sources for a.a.s. Arsenic and selenium can be determined at very low concentrations (ng ml^-1) by the hydride generation technique. Sulphur and phosphorus can be detected in the vacuum ultra-violet region using nitrogen-separated flames; the limits of detection are 13 and 10 μg ml^-1, respectively.     

Determination of ZnSe(Te) stoichiometry and dopant content by X-ray analysis

Summary Light output and response duration of isovalently doped zinc selenide single crystals depend on their element composition as well as on the dopant content and its distribution. For monitoring of these parameters, X-ray analysis suits best of all and was developed here. The ratio of Kα line intensities of Se and Zn was derived for the determination of ZnSe(Te) stoichiometry by taking into account the contribution of secondary excitation. The linear dependence of the TeKα intensity on the Te content was used for determining the latter. An annular ¹⁰⁹Cd source was used for the excitation of Zn and Se Kα-lines and the Kα line of Te was excited by three ²⁴¹Am sources. The measurement error (Sr) of ZnSe elemental composition was 0.01. The measurement error of the Te content was 0.06-0.09 in the range of 0.01-0.5% Te.     

Ce和Dy在Cd0.5Zn0.5B4O7中的发光特性及能量双向传递

采用高温固相法制备了白蓝光双发射为一体的Cd0.5Zn0.5B4O7∶Ce/Dy系列发光材料. 由XRD测得Cd0.41Zn0.5B4O7∶Ce0.04/Dy0.02的晶胞参数: a=1.3885 nm, b=0.8020 nm, c=0.8670 nm, 属于正交晶系, Pbca空间群. 在Ce/Dy双掺的体系中存在Ce3+和Dy3+两种发光中心, 254~350 nm激发主要是Dy3+的 4F9/2→6H15/2和4F9/2→6H13/2跃迁发射, 而355—390 nm激发主要为Ce3+的5d→4f跃迁发射. 340 nm激发Ce/Dy双掺发光体的发射强度是同浓度Dy3+单掺的31倍, Ce3+是Dy3+的高效敏化剂, 而355—390 nm激发Dy3+是Ce3+的敏化剂. 体系中存在少见的Ce3+→Dy3+与Dy3+→Ce3+的能量双向传递.     

Establishment of SI-traceable reference values for the content of various elements in the IMEP-14 sediment sample

For the first time in the International Measurement Evaluation Programme (IMEP)-14, a sediment sample was offered to analytical laboratories to perform measurements of As, Cd, Cr, Cu, Fe, Pb, Hg, Ni, U and Zn. In line with IMEP policy, the results were presented according to the certified / assigned reference values established by several reference laboratories around the world. The certification campaign is described in detail. Isotope dilution mass spectrometry was applied as a primary method of measurement, whenever possible, to achieve SI-traceable results. For reference measurements of As, Fe, Hg and Zn, k₀-neutron activation analysis and Zeeman atomic absorption spectrometry were applied. The reference values (ranges) were characterised as ”certified” (for Cd, Cr, Pb, Ni and U) or ”assigned” (for As, Cu, Fe, Hg and Zn) according to IMEP policy. The measurement uncertainty of the certified / assured reference values was calculated according to the ISO/BIPM Guide. Received: 7 June 2001-10-27 Accepted: 19 August 2001     

Ion-chromatographic trace analysis of mercury, cadmium and zinc by post-column derivatisation with a water-soluble porphyrin

Summary A post-column derivatisation system with mesotetra (4-sulfonatophenyl)-porphyrin (TPPS₄) and PAR as accelerating agent in a borate buffer pH 11.5 in the presence of tartrate and NaCl is proposed. The complexes of Cd, Zn and Hg have maximum absorption at 430 nm. The separation system consists of silica-gel chemically bonded cation exchanger as stationary phase and a tartrate-NaCl solution as mobile phase. The separation can be finished within 10 min. The calibration curves of these metal ions with the peak area of the chromatogram were found to be linear in the range of 0.002–0.8, 0.1–8.0 and 0.05–20.0 mg/l for Cd, Hg and Zn. The detection limits for Cd, Hg and Zn are 0.05, 5 and 1 ng. This new method was applied to the analysis of waste water, silicates and corn with satisfying results.

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Ionen-chromatographische Spurenanalyse von Hg, Cd und Zn durch Nachsäulen-Derivatisierung mit einem wasserlöslichen Porphyrin

     

Simultaneous determination of Cd and Fe in sewage sludge by high-resolution continuum source electrothermal atomic absorption spectrometry with slurry sampling

This work describes the method development for the simultaneous determination of Cd and Fe using the main resonance line of Cd at 228.802 nm and a secondary Fe line at 228.725 nm, and high-resolution continuum source electrothermal atomic absorption spectrometry (HR-CS ET AAS). Two certified reference materials and two ‘real’ samples of industrial and domestic sewage sludge have been analyzed as slurries prepared in a mixture of HF and HNO₃. The simultaneous determination has been performed using a short temperature program of only 30 s, without a pyrolysis stage and with two atomization stages, at 1300 °C and 2300 °C, taking into consideration the significantly different thermal characteristics of Cd and Fe. Structured background, which is likely due to the presence of one or more diatomic molecules, including SiO, has been detected. However, there has been no spectral overlap between molecular bands and the atomic lines of Cd and Fe, making possible the determination to be carried out using only automatic correction for continuous background. Calibration against aqueous standards lead to good agreement between certified or informed values and the determined values, at a statistical confidence level of 95%; recovery tests were performed for real samples, resulting in recoveries ranging from 90 to 105%. Detection limits of 0.03 and 90 µg g^{− 1} for Cd and Fe, respectively, have been obtained, which are adequate for the purpose.     

Determination of traces of lead,cadmium and zinc in copper by an arc-nebulization and flame atomic absorption technique

Arc-nebulization (a thermal nebulization technique) is used to form an aerosol of cadmium, lead and zinc. An open arc chamber of simple operation and an ejector of high efficiency are described which are adaptable for use with any flame atomic absorption spectrometer. Limits of detection better by one or two orders of magnitude than those achieved by conventional flame a.a.s. methods were obtained viz., 43 ng Pb, 5 ng Cd, 7 ng Zn (equivalent to 0.7, 0.08 and 0.11 ppm, respectively, in copper). Calibration with matrix-free solutions was possible for lead and cadmium but not for zinc. The spectral interference of copper on absorbance at the most sensitive zinc line (213.856nm) and the efficiency of arc nebulization of cadmium are also discussed.     

Chelation of urinary cadmium with ammonium pyrrolidine dithio-carbamate prior to determination by tungsten-coil inductively coupled plasma atomic emission spectrometry

Cadmium in the urine samples of patients with age-related disease forms a complex with a chelating agent, ammonium pyrrolidine dithio-carbamate, and the complex is extracted with methyl isobutyl ketone. One milliliter of urine provides three separate 200-μl aliquots of extract, so a preconcentration factor of 5/3 is observed. In this manner, the Cd is effectively separated from the complex urine matrix. An internal standard, Bi, is added to improve both precision and accuracy. The extracts are analyzed by inductively coupled plasma atomic emission spectrometry using a tungsten-coil as an electrothermal vaporizer. A 20-μl aliquot of the extract is injected directly onto the coil. Two Cd atomic emission lines are observed simultaneously: 228.8 nm and 226.5 nm. The limits of detection at these wavelengths are 0.04 and 0.2 μg/l, respectively. Without the extraction technique, the detection limit is 0.4 μg/l at the 228.8-nm line. With the internal standard technique, the accuracy as measured with a urine standard reference material is 98%. Six urine samples collected from patients with age-related diseases are found to contain Cd levels in the range 0.9 to 4.1 μg/l. The precision associated with the measurement of these real samples is 6.2% relative standard deviation. The technique provides off-wavelength background correction and simultaneous determination at two different wavelengths, so samples that are limited in volume can still be analyzed with a high degree of confidence.     

Some observations on the chemiluminescence of atoms in acetylene flames supported by air and argon-oxygen mixtures

A study has been made of the chemiluminescent emission of As, Bi, Cd, Ge, Hg, I, Mo, Pb, Sb, Se, Sn, Te, V and Zn in the primary combustion zones of air-acetylene and argon-oxygen-acetylene flames, supported at an open burner port during the aspiration of aqueous solutions of their salts. In general, elements having excitation, potentials greater than 4 eV show considerably greater atomic chemiluminescence in the primary zone than “thermal” atomic emission in the interconal region. Various mechanisms are suggested for the energy-transfer reactions between metal atoms and excited flame species, particularly carbon monoxide.