Improved Method for Making Electrodeless Discharge Lamps

Abstract

Arsenic electrodeless discharge lamps have been made with arsine gas as the source of arsenic. Lamps using arsine have been shown to be reproducible, intense, stable and long lived.     

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.     

The Determination of Bismuth By Hydride Generation and Non-Dispersive Atomic Fluorescence Detection

Abstract

A sensitive determination of bismuth by hydride generation with non-dispersive atomic fluorescence spectrometric detection is proposed. A commercially available electrodeless discharge lamp was used as the light source. Studies on interference effects from foreign elements are reported and the determination of bismuth in copper metal was considered in detail.     

Trace analysis by microwave excitation of sealed samples-III Determination of 0.005-25 ng of Te and 0.25-25 ng of Se in 0.5 ml of aqueous solution

Traces of tellurium and selenium can be determined by optical emission spectrometry using microwave exitation in electrodeless discharge lamps. In 0.5 ml aqueous solution samples, freeze-dried in electrodeless discharge lamps, 10(-5) ppm Te and 5 x 10(-4) ppm Se can be determined with a relative deviation of about 20%.     

Etude des spectres d'émission atomique du néon et du xénon entre 3,5 et 5,5 μm à l'aide d'un spectromètre à grilles

It has been possible to observe spontaneous emission lines of Neon and Xenon with s Girard grid spectrometer up to 5.5 μm. We obtained a limit of resolution of 0.060 cm⁻¹. The source used was an electrodeless discharge tube with a sapphire window.     

Thermostated radio-frequency excited electrodeless discharge lamps as primary sources in AFS

The performance of Cd and Zn thermostated electrodeless discharge lamps (EDL's) excited at 150 MHz radio-frequency through the inductively-coupled mode in a coil, have been studied with respect to the effect of lamp temperature, amount of material and RF power upon the source radiant output, atomic absorption, atomic fluorescence signals, spectral line width and line profile height of Cd 479.99 nm, Cd 228.8 nm, Zn 481.05 nm and Zn 213.9 nm. Although the lamps show similar behaviour to their microwave excited counterparts, they nevertheless offer several advantages that could renew the interest in EDL's as primary excitation sources in analytical spectroscopy.     

Studies in atomic-fluorescence spectroscopy-VI The fluorescence characteristics and analytical determination of bismuth with an iodine electrodeless discharge tube as source

The atomic-fluorescence characteristics of bismuth atoms in cool nitrogen-hydrogen and argon-hydrogen diffusion flames burning in air are described. Excitation is obtained from the non-resonance iodine line at 2061.63 Å emitted by a microwave-excited electrodeless discharge tube operating at 2450 Mc/s. Fluorescence of the bismuth resonance line at 2061.70 Å is observed and also direct-line fluorescence at 2697 and 3025 A. In addition thirteen other much weaker lines were observed and two unidentified lines at 2880 and 2680 Å. The emissions at 2628 and 2938 Å appear to arise from “thermally assisted direct line fluorescence”. The most intense line at 3025 Å permits linear-dependence analytical atomic-fluorescence measurements to be made in the range 0.1–200 ppm with a detection limit of 0.05 ppm and with no problems of source scatter. No interference was observed from hundred-fold concentrations of fourteen ions. Matrix effects from aluminium and magnesium were overcome by raising the temperature of the cool diffusion flames. A bismuth microwave-excited electrodeless discharge tube was used as a source for atomic-absorption measurement in air-hydrogen and air-propane flames at 2231Å with a detection limit of 1 ppm and a linear-dependence analytical range of 10–100 ppm. With the iodine microwave-excited electrodeless discharge tube the detection limit for atomic absorption was 10 ppm at 2062 Å.     

Performance of a microwave induced plasma (MIP) operated in a liquid-cooled discharge tube for atomic emission spectrometry

Different types of microwave induced plasma (MIP) discharge operated in liquid-cooled tubes, namely a glass tube of Duran^®, a quartz tube of Herasil^®, and a very simple demountable discharge tube made of glass and quartz have been investigated. The last tube leads to the best analytical properties and the longest lifetime. The intensities of silicon lines and of the continuum spectral background, together with the signal-to-background ratios for B, Ca, Cd, Co and Zn in the case of the pneumatic nebulization of solutions have been measured and used as an indicator for the cooling efficiency. The MIP torch was cooled with a thermostated silicon oil. The decrease of the temperature of the cooling medium causes a measurable decrease of the spectral background intensity. Diagnostic measurements of the plasma include radial profiles of spectral line intensities and excitation temperatures with the lines of Fe I; values of 5000–6000 K are found. The influence of different plasma parameters, e.g. microwave power and helium flow rate, is investigated. The preliminary analytical characterization of a helium MIP maintained with the liquid-cooled demountable discharge tube is presented. Limits of detection for Al, B, Ca, Co, Fe, P, Sb and Zn (between 0.002 and 1.2 μg ml⁻¹) are comparable with or better than those reported for low power helium MIPs with sample introduction in the form of a wet aerosol.     

A reproducible method for preparation and operation of microwave excited electrodeless discharge lamps: SIMPLEX optimization of experimental factors for a cadmium lamp

By means of a SIMPLEX optimization procedure, cadmium electrodeless discharge lamps (EDLs) operated at microwave frequencies (2450 MHz) were prepared and optimized with respect to: weight of cadmium, W₁ = 680–750 μg; time interval of the EDL blank under vacuum after water removal, t₁ = 0–1000 s; pressure of argon gas (under microwave excitation) during preparation, A₁ = 1–2.5 torr; microwave power for discharge during preparation, P₁ = 90–10O W; time interval for microwave discharge during preparation, t₂ = 20–28 s; time for EDL to cool before evacuation, t₃ = 240 s; time under vacuum after cooling period, t₄ = 0–500 s; pressure of argon to fill lamp, A₂ = 6–9 torr; microwave power for operation of EDL, P₂ = 55–65 W; and operating temperature of EDL, T = 290–330°C. Under the above conditions, EDLs were prepared reproducibly (atomic fluorescence detection limits were all within a factor of 3 or less). The resulting EDLs were consistently as good as or better than the best EDLs prepared in the past by the laboratory. Throughout the SIMPLEX optimization procedure, no EDL failed; all EDLs behaved as would be predicted by the preparation procedure.     

Cadmium Determination in Sedimented Dust by Atomic Emission Spectrometry With a New Radiofrequency Capacitively Coupled Plasma Source

ABSTRACT

A new radiofrequency capacitively coupled plasma source (r.f.CCP) was used for Cd determination in dust samples by atomic emission spectrometry. The plasma torch consists of a molybdenum tube electrode and one or two ring electrodes situated outside the quartz tube. Plasma was operated at 27.12 MHz, at low power (275 W) and low gas consumption (0.4 1 min^? argon flow). The choice of the optimum operating conditions for Cd determination in dust samples dissolved in acids and pneumatically nebulized is presented. The results obtained in such samples were compared with those obtained by flame atomic absorption spectrometry (FAAS). The matrix effect of NaCl and CaCl₂ on Cd emission was also studied depending of the plasma coupling system. The true limit of detection for Cd in dust sample by r.f.CCP-AES is 3 μg g^?1. Concentration of Cd higher than 10 μg g^?1 can be determined by the proposed method with a relative standard deviation within the range 5 - 10%. The recovery is 100 ± 10%.     

Controlled temperature-gradient atomic spectral lamp

The lamps are based on excitation of a thermally-produced vapour in a low-pressure gas discharge. For arsenic and selenium, the resonance line intensities are five times higher than those emitted by electrodeless discharge lamps for the same line-widths. Limits of detection are 16 ng ml^-1 for arsenic and selenium in non-dispersive atomic fluorescence measurements; sensitivities are also improved in atomic absorption.     

Characteristics of a novel UV-TiO2-microwave integrated irradiation device in decomposition processes

The efficiency of oxidation in wet decomposition procedures for organic materials can be of great importance to the quality of the analytical data from various measurement techniques. A novel, microwave-assisted, high-temperature/high-pressure UV-TiO₂ digestion procedure was developed for the accelerated decomposition of various biological samples. The technique is based on a closed, pressurized, microwave digestion apparatus (MW). UV irradiation is generated by immersed electrodeless Cd discharge lamp operated by the focused microwave field in the single polymer vessel. To enhance oxidation efficiency, a photocatalyst TiO₂ was added to the microwave heated Teflon bomb. Measures of digestion completeness were provided by the appearance of carbon content and determination of trace and minor elements, enabling a comparison of different digestion procedures and sample types. Compared with other digestion systems, unusually low residual carbon contents were obtained. For the organic compounds and biological samples digested, the residual carbon content was 1-2%, corresponding to a decomposition efficiency of 98-99%. The potential of the MW-UV-TiO₂ system was illustrated by the decomposition of four certified reference materials (serum, urine, milk, arsenobetaine solution) and subsequent determination of trace and minor elements. Recoveries between 92% and 107% were found.     

The determination of uranium isotopes by atomic absorption spectrophotometry

The uranium isotopes, ²³⁵U and ²³⁸U, can be determined easily by atomic absorption techniques, employing relatively inexpensive and unsophisticated equipment. A water-cooled hollow-cathode discharge tube was used as an absorption tube. It was found that large amounts of uranium atoms, in the ground state, were produced by the discharge in the tube. Thus the inherently weak uranium resonance radiation coming from. an emission source and passing through the absorption tube was absorbed. For the first time in an atomic absorption technique, samples and related standards were used in the emission source instead of an absorption source, and a high degree of accuracy and precision was obtained. Valid results were also obtained by conventional techniques — that is, the samples and related standards were employed in the absorption source.     

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.     

Ammonia-filled discharge tubes for optical emission spectrometric determination of 15N : 14N isotope ratios

A procedure is described for filling a discharge tube, permanently attached to a vacuum line, with ammonia in the pressure range 1.5–5 Torr, without any carrier gas. The ¹⁵N : ¹⁴N isotope ratio is determined from the N₂ spectrum emitted when the tube is excited by a 2450-MHz microwave source. Cooling one end of the discharge tube to —60°C enables the N₂ (1,0) bandheads at 316 nm to be used for ¹⁵N contents down to about 0.04 atom-%. Unidentified interfering bands and emission from NH, OH, H₂ and H are discussed. Samples containing 1–30 mg of nitrogen can be analysed with an accuracy and precision suitable for most soil—plant studies employing ¹⁵N as a tracer.     

Cadmium Determination in Soil Extracts by Furnace Atomic Absorption

Abstract

A method for the direct determination of Cd in soil extracts by graphite furnace atomic absorption spectrosopy (GFAAS) has been developed. Optimum operating conditions, analyte modifiers and matrix interferences have been investigated. Characteristic amounts are 0.34pg for siliceous samples and 0.45 pg for calcareous soils. The precision has been based on ten replicate readings in standards, and was 1.6%. Cd has been determined by the proposed methods and the results have been compared with those obtained by ICP technique.     

Determination of metal concentrations in lichen samples by inductively coupled plasma atomic emission spectroscopy technique after applying different digestion procedures

Three digestion procedures have been tested on lichen samples for application in the determination of major, minor and trace elements (Al, Ca, Cd, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, Pb, V and Zn) in lichen samples collected in Aegean Region of Turkey by inductively coupled plasma atomic emission spectrometer (ICP-AES). The acid mixture of concentrated HNO₃, H₂O₂ and HF were used. The instrument was optimized using lichen matrix considering RF power, nebulizer pressure, auxiliary flow rate and pump rate. The accuracy of the overall analyses was first estimated by analysis of two certified reference materials. Good agreement between measured and reference values were found for almost all elements. As the second way of determining the accuracy, results obtained from independent analytical techniques (ICP-AES and instrumental neutron activation analysis (INAA)) were compared for all elements by analyzing real samples. Correlation coefficients of two techniques for the elements ranged between 0.70 (Mg) and 0.96 (Fe). Among the three digestion systems, namely microwave, open vessel and acid bomb, microwave digestion system gave the best recovery results. The method detection limit (MDL) was computed using reagent blanks of microwave digestion system since it provides cleaner sample preparation. Detection limit is adequate for all elements to determine the elements in lichen samples. The precision was assessed from the replicate analyses of reagent blanks of microwave digestion system and was found to be less than 1.5% relative standard deviation (R.S.D.).     

Three-filament and toroidal microwave induced plasmas as radiation sources for emission spectrometric analysis of solutions and gaseous samples—II: Analytical performance

The generation of two new types of the Ar-MIP and their analytical performance as radiation sources for atomic emission spectrometry in the extreme trace analysis of elements is described. A stable 3-filament Ar-MIP, and a toroidal Ar-MIP can be generated in a cylindrical TM₀₁₀ cavity with special mountings and adjustment devices for the discharge tube. The first was found to be suitable for the determination of volatile elements or compounds and the latter for the analysis of solutions subsequent to pneumatic nebulization. The influence of different plasma parameters, e.g. microwave power and argon gas flow was investigated. The detection limits for the elements Be, Ca, Cd, Co, Cr, Cu, Ga, Hg, Mg, Mn, Sr, Tl and Zn were found to be in the range of 1–50 ng ml^?1. As an example for the application of the toroidal MIP, analyses of natural water samples (drinking water, glacial ice and snow) were performed.     

Preparation of electrodeless discharge lamps for emission studies of uranium isotopes at trace level

A simplified method for preparation of electrodeless discharge lamp for uranium isotopes with specific concerns for ²³²U is described. Micro-gram quantities of solid uranium oxides and aqueous solution of uranium nitrate have been used as a starting material for in situ synthesis of uranium tetraiodide. High temperature iodination reaction is carried out in the presence of inert gas neon. By careful design, the preparation time and surface area of quartz reaction tubes have been reduced considerably. The latter decreases the level of contamination which has a direct bearing on the operational lifetime of the lamps. Incorporation of steps to purify the product from an unwanted material improved the stability of the lamps. The procedure provides a safe and convenient way of handling ²³²U in particular but can be extended in general to any actinides having radioactivity similar to that of freshly separated ²³²U. Characteristic emission of uranium isotopes have been recorded by Fourier Transform Spectrometer to show the satisfactory operation of the lamps as well as their usage for studying emission spectra of the specific isotope.     

Production of XeO* in a CW microwave discharge

A low-power CW microwave discharge at 2.45 GHz was used to produce XeO^* excimer molecules. It was found that a total gas pressure between 5 and 20 Torr, absorbed power of about 20–100 W, and an oxygen-to-xenon ratio of 1100 maximized the XeO(¹S–¹D) green emission at 5200 to 5600 Å. The XeO^* emission appeared in the cooler parts of the discharge near the containment tube walls and in the electric field nodes of the TM₀₁₂ resonant mode.