Studies in atomic-fluorescence spectroscopy-VII Fluorescence and analytical characteristics of arsenic, with a microwave excited electrodeless discharge tube as source

The construction of an electrodeless arsenic discharge tube and its use for atomic-fluorescence studies is described. Cool nitrogen-hydrogen and argon-hydrogen diffusion flames as well as normal premixed flames are considered as atom reservoirs and the atomic-fluorescence emission at 15 different wavelengths is evaluated. The diffusion flames give the largest emission signals at arsenic concentrations below 200 ppm, but show a premature curvature at higher concentrations because of the presence of an abnormally high density of arsenic atoms. Above 200 ppm of arsenic, the premixed air-acetylene flame is superior. The limit of detection at 1890 A is 0.2 ppm of arsenic in the nitrogen-hydrogen diffusion flame and 1.0 ppm in the airacetylene flame. A long path-length diffusion flame is also particularly useful in atomic-absorption measurements because it absorbs very little radiation in the far ultraviolet region and gives an abundance of arsenic atoms.     

Atomic-fluorescence characteristics and analytical determination of manganese in an air-acetylene flame

The atomic-fluorescence characteristics of manganese atoms in a premixed nitrogen-shielded air-acetylene flame are described. Excitation is obtained at 280 nm from a microwave-excited electrodeless discharge tube. A detection limit of 0-001 ppm for the determination of manganese by atomic-fluorescence spectroscopy is obtained by measurement of the resonance fluorescence observed at this wavelength. In addition to several other weaker atomic-fluorescence signals observed from manganese atoms in the flame, weak resonance fluorescence at 258 and 260 nm from manganese ions stimulated by ion line-emission from the source has been recorded. Linear calibration graphs for atomic-fluorescence measurement at 280 nm are obtained over the range 0.0025-10 ppm of manganese in aqueous solution. Of 26 foreign anions and cations examined for interference at the 1000-fold weight excess level only four produced interference. Large amounts of Si, Th and V interfere by scattering of the incident radiation, while Mg causes depression of the atomic fluorescence by a chemical effect.     

Spectroscopy in separated flames--VII: Determination of bismuth by atomic-fluorescence spectroscopy in a separated air-acetylene flame with electronically modulated electrodeless discharge tube sources

The application of electronically modulated and unmodulated bismuth and iodine electrodeless discharge lamps as sources for the excitation of bismuth atomic fluorescence in conventional and nitrogen-separated air-acetylene flames has been investigated. Separation of the flame results in improved detection limits for bismuth even when a modulated source is employed. The effect of 500-fold weight excesses of foreign ions on the determination of bismuth at 302.46 nm with a modulated iodine source and separated flame has been studied; only calcium and zirconium are found to cause significant interference. The determination of bismuth in aluminium alloy samples is reported.     

Studies in atomic-fluorescence spectroscopy-III Microwave-excited electrodeless discharge tubes as spectral sources for atomic-fluorescence and atomic-absorption spectroscopy

Details are given for the production and operation of microwave-excited electrodeless discharge tubes for use as sources in atomic-fluorescence and atomic-absorption spectroscopy. Special reference is made to the tubes for selenium and tellurium and their spectral characteristics are fully discussed. Optimum conditions are given for producing suitably intense and stable sources.     

Studies in atomic-fluorescence spectroscopy--VIII. Atomic fluorescence and atomic absorption of thallium and mercury with electrodeless discharge tubes as sources

Atomic-fluorescence measurements, with microwave-excited electrodeless discharge tubes as sources of excitation, are described for thallium and mercury. The limits of detection by atomic fluorescence are 0.12 ppm for thallium and 0.08 ppm for mercury; the corresponding limits by atomic absorption (using the same instrument and source) are 6 and 10 times as great. The preparation, operation and spectral characteristics of thallium and mercury discharge tubes are described and comparisons are made with a thallium hollow cathode lamp and thallium and mercury spectral discharge lamps.     

The determination of lead by atomic fluorescence spectroscopy

The atomic fluorescence characteristics of lead are described in air-acetylene, nitrous oxide-hydrogen, and argon-oxygen-hydrogen flames. An electrodeless discharge tube is used as the source of excitation. A detection limit of 0.01 μg/ml of lead in aqueous solution is obtained by measurement of the direct-line fluorescence at 405.8 nm in the argon-oxygen-hydrogen flame. The effect of 100-fold excesses of 30 cations and anions is examined: only aluminium interfered significantly. Effects of multipass optics and signal collection mirrors are examined and their effect on signalnoise ratios is discussed.     

Studies in atomic-fluorescence spectroscopy-V The fluorescence characteristics and determination of antimony

Atomic-fluorescence of antimony may be generated in an air-propane flame by nebulizing aqueous solutions of antimony salts whilst irradiating the flame by means of a microwave-excited electrode-less discharge tube operating at 30 W. The strongest fluorescence is exhibited by the (4)S(11 2 ) --> (4)P(1 3 ) 2311 A resonance line and weaker signals are observed at the 2068 and 2176 A resonance lines and at four intercombination lines, at 2598, 2671, 2770 and 2878 A. A process of thermally assisted direct-line fluorescence is postulated to account for the otherwise inexplicable intensity of the 2598 A line emission. Atomic-fluorescence spectroscopy at 2176 A permits the determination of antimony in the range 0.1-120 ppm with a detection limit of 0.05 ppm. With the same equipment and source, the range of measurement for atomic-absorption was 6-120 ppm and the detection limit was 1 ppm. No interferences were observed from 100-fold molar amounts of Cd, Co, Cu, Fe, Hg, K, Mg, Mn, Mo, Na, NH(4), Pb and Zn or from arsenate, chloride, nitrate, phosphate and sulphate.     

A simultaneous multielement non-dispersive atomic-fluorescence spectrometer using modulated sources and frequency discrimination of fluorescence signals

Commercial radiofrequency-excited electrodeless discharge lamps can be run from a square-wave modulated power supply so as to give a low level of continuous emission when modulated in the frequency range 3–10 kHz. Use of a different modulation frequency and lock-in amplifier for each lamp allows multielement non-dispersive atomic-fluorescence spectrometry to be performed. Very low detection limits have been obtained for arsenic, selenium, tin and mercury. The use of low-cost electronic components in the system largely offsets the high cost of the individual excitation power supplies and tuned a.c. detectors.     

Non-dispersive atomic-fluorescence spectrometric determination of lead by the hydride-generation technique

Non-dispersive atomic-fluorescence spectrometry combined with hydride-generation has been developed for lead determination. A radiofrequency-excited electrodeless discharge lamp was used as light-source and a small argon-hydrogen flame as atomizer. The detection limit was 0.06ng/ml and the linear calibration graph was linear up 300ng/ml, with a precision of 5-6% over the dynamic range. Interference studies and optimization of the experimental parameters are reported. Severe suppression of the lead signal was observed in presence of Cu, Se or Te. An empirical equation was obtained for predicting the effect of copper on the lead signal at various concentration ratios. The strong effect of complexing agents such as EDTA was removed by addition of zinc salts.     

Studies in atomic-fluorescence spectroscopy-IV The atomic-fluorescence spectroscopic determination of selenium and tellurium

Selenium and tellurium are determined down to 0.25 and 0.12 p pm respectively by measuring the atomic-fluorescence signals at 2040 A and 2143 A respectively. Other possible wavelengths of measurement are considered in detail and the effects of some extraneous ions are examined. Microwave-excited electrodeless discharge tubes are used as spectral sources and intensity measurements are made with a Unicam SP 900A atomic-absorption/flame-emission spectrophotometer. Atomic-absorption measurements are also made with the same sources and spectrophotometer. The advantages of atomic-fluorescence methods and the use of electrodeless discharge tubes are discussed.     

Spectroscopy in separated flames-IV: application of the nitrogen-separated air-acetylene flame in flame-emission and atomic-fluorescence spectroscopy

The primary and secondary combination zones of an air-acetylene flame have been separated by a stream of nitrogen flowing parallel to the flame to prevent access of atmospheric oxygen to its base. The flame is very stable over a wide range of fuel-air mixture strengths, and organic solvents may be aspirated without difficulty. The low flame background enables thermal-emission and atomic-fluorescence measurements to be made with high sensitivity. Bismuth, for example, has been determined in the range 5-200 ppm by its thermal emission at 306.8 nm, with a detection limit of 2 ppm in aqueous solution, and in the range 1-10 ppm with a detection limit of 0.3 ppm in 50% ethanolic solution. Zinc and cadmium have been determined at 213.9 nm and 228.8 nm by atomic-fluorescence spectroscopy in this flame with detection limits of 2 x 10(-4) ppm and 5 x 10(-4) ppm respectively, vapour-discharge lamps being used as sources of excitation. The results obtained represent a considerable improvement over those available by the same methods in a conventional air-acetylene flame.     

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.     

Determination of iodine by atomic-absorption spectrometry using the platinum-loop technique

The use of a platinum-loop atomizer and an electrodeless discharge lamp has been applied to the atomic-absorption determination of mercury at the 183.0-nm resonance line. Oxygen was flushed from the light-path with argon, giving adequate readiation transmission characteristics and a sensitivity of 9 ppm of iodine for 1% absorption. The method is prone to both cationic and anionic interferences, but the use of cation-exchange and solvent-extraction procedures overcomes some of the problems.     

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.     

Non-dispersive atomic-fluorescence spectrometry of trace amounts of bismuth by introduction of its gaseous hydride into a premixed argon (entrained air)-hydrogen flame

A method has been developed for the determination of bismuth by generation of its gaseous hydride and introduction of the hydride into a premixed argon (entrained air)-hydrogen flame, the atomic-fluorescence lines from which are all detected by use of a non-dispersive system. The detection limit is 5 pg/ml, or 0.1 ng of bismuth, but the reagent blank found in a 20-ml sample volume was approximately 2 ng of bismuth. Analytical working curves obtained by measuring peak-heights and integrated peak-areas of the signals are linear over a range of about four orders of magnitude from the detection limit. Perchloric, phosphoric and sulphuric acids up to 2.0M concentration give no interference, but nitric acid gives slight depression of the signal. The presence of silver, gold, nickel, palladium, platinum, selenium and tellurium in 1000-fold ratio to bismuth causes pronounced depression of the signal, whereas mercury and tin slightly enhance the atomic-fluorescence signal. The method has been applied to the determination of bismuth in aluminium-base alloys and sulphide ores with use of the standard additions method. The results are in good agreement with those obtained by flame atomic-absorption spectrometry and optical emission spectrometry with an inductively coupled plasma.     

Crystal structure of Fe(η-C5H5BCMe3)2 a “problem structure”

The complex Fe(η⁶-C₅H₅CMe₃)₂ crystallizes in the centrosymmetric triclinic space group P (C_i¹; No. 2) with unit cell dimensions of a 8.770(1) Å, b 8.878(1) Å, c 11.991(1) Å, 107.56(1)°, β 90.85(1)°, γ 90.13(1)°, V 890.0(2) ų and Z = 2. A full sphere of data was collected on a four-circle diffractometer. The structure was solved and refined to R 7.93% for all 3155 independent reflections and R 4.98% for those 2002 data with | F₀ | > 6σ. | F₀ |. The molecules lie on crystallographic inversion centers at 0, 0, 0 and 1/2, 0, 1/2; the crystallographic asymmetric unit therefore consists of two independent half molecules. The molecule centered at 0, 0, 0 (molecule “A”) is ordered and well-defined; that centered on 1/2, 0, 1/2 (molecule “B”)is probably disordered, as indicated by larger “thermal parameters” and a greater range of apparent interatomic distances. Discussion em phasizes the geometry of molecule A, which has precise C_i symmetry with Fe(1A)-B(1A) 2.297(4) Å and Fe(1A)-C(ring) distances ranging from 2.057(6) Å to 2.138(4) Å.     

Determination of manganese by atomicpluorescence spectroscopy using a carbon-filament atom-reservoir

The atomic-fluorescence characteristics of manganese heated on a carbon-filament atom-reservoir (CFAR) are described and compared with (a) the atomic-absorption behaviour of the element on the same filament apparatus, and (b) its fluorescence behaviour in a separated air-acetylene flame. By fluorescence at 279.5 nm, using 1-mul samples, manganese may be determined down to 0.6 pg (6 x 10(-4) ppm) by use of an electrodeless discharge lamp source (3 pg or 3 x 10(-3) ppm by absorption, and 20 ng or 1 x 10(-2) ppm by flame emission at 403 nm). The effects of fourteen representative cations and anions examined showed no interference at 10-fold and 100-fold levels and serious interference only from magnesium at the 1000-fold level, with ca. 10% suppression from Cr, V, Na and K. No fluorescence signals were observed at any wavelength other than 279.5 nm when the CFAR device was used.     

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.     

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.     

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%.