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.     

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.     

Non-dispersive atomic-fluorescence spectrometry for the determination of mercury and its application to fish samples.

A simple non-dispersive atomic-fluorescence spectrometer is described for the assay of mercury in solution at the μg l^?1 level; it has also been applied to fish samples at the mg kg^?1 level. After destruction of the fish sample, the mercury is reduced by tin(II) chloride and released from solution by a stream of argon which crosses the beam of a mercury lamp. The fluorescence signal is detected directly by a solar-blind phototube without the need for monochromators or filters. One analysis requires less than 40 min. The results correlate well with those from atomic-absorption spectrometry and neutron-activation analysis.     

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.     

A graphite-tube furnace for use in laser-excited atomic-fluorescence spectrometry

The construction and performance of a graphite-tube furnace for use in laser-excited atomic-fluorescence spectrometry are evaluated. The graphite-tube furnace gives better detection limits than a cup-furnace does for the non-volatile elements.     

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.     

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.     

Use of a filter in atomic-fluorescence spectroscopy

A detecting system incorporating an interference filter is described for use in atomic-fluorescence spectroscopy analysis in the 200.0-300.0 nm spectral region. Results obtained by using this system are compared with those from a detecting system incorporating either a monochromator or a solar-blind photomultiplier. Improvements of approximately 700-fold and 10-fold respectively in the limits of detection for zinc and mercury result from replacing the monochromator with the filter, while results with the filter are similar to those from a solar-blind photomultiplier. Limits of detection of 10(-5) ppm for zinc and 2.5 x 10(-4) ppm for mercury, both in aqueous solutions aspirated into an air-town-gas flame, are an improvement on other published results for these elements, obtained by atomic-fluorescence flame spectroscopy.     

Evaluation of a pulsed EIMAC source for atomic-fluorescence spectrometry

An EIMAC xenon arc continuum source operated in the pulsed mode has been evaluated for potential use as a source of excitation in atomic-fluorescence spectrometry. The results were compared with those obtained with a similar lamp operated in the continuous-wave mode; little or no improvement was evident from this comparison. The lamp was found to be unstable in the pulsed mode, requiring the use of a rather large residual d.c. current in conjunction with a relatively low amplitude power-pulse in order to sustain the arc. Moreover, the pulsed source yielded a large background signal because of scattering of source-radiation in the flame; the background spectrum (with source "on") contained numerous large peaks due to fluorescence of molecular species in the flame and to irregularities in the spectral distribution of the pulsed lamp output transmitted to the signal detector by scatter.     

Determination of zinc in copper by atomic-fluorescence flame spectroscopy

The application of atomic-fluorescence flame spectroscopy to the determination of trace quantities of zinc in copper is described. A limit of detection of 10(-5)% zinc in copper has been established. The scatter of primary radiation from within the flame determined the limit of detection, but it is suggested that scatter is not a serious limitation to the practical application of the technique.     

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.     

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.     

Determination of copper in urine by carbon-furnace atomic-emission spectrometry

A method is described for the direct determination of copper in urine at normal (10-30 mug l .) levels by carbon-furnace atomic-emission spectrometry. Wavelength modulation is used to achieve automatic background correction for scatter-signals produced by the furnace and matrix. The accuracy of the method has been assessed by comparison with continuum-source atomic-fluorescence and carbon-furnace atomic-absorption methods. Relative standard deviations of about 4-5% can be achieved for either the platform or probe atomization techniques.     

Determination of part-per-milliard concentrations of mercury by atomic- fluorescence flame spectrometry

A method is reported for the determination of mercury in the range 0.002-1 microg/ml . Mercury is extracted by dithizone from aqueous solutions into chloroform or isobutyl methyl ketone, the organic solution is aspirated into a hydrogen-oxygen name, and the intensity of atomic-fluorescence of mercury is measured. The method should be particularly useful for the determination of mercury in urine and for the determination of organic-bound mercury without prior decomposition.     

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.     

Electrothermal atomic-absorption and atomic-fluorescence spectrometry with a tungsten-coil atomizer

A pulsed electrothermal atomizer of the tungsten-coil type and apparatus for its application in atomic-absorption and atomic-fluorescence spectrometry are described. A tungsten-coil atomizer is shown to be just as good as commercial electrothermal atomizers with regard to sensitivity and reproducibility, but to have better operating characteristics. A theoretical model for formation of the atom cloud is given. Mechanisms for atomization of different groups of element in an atmosphere of pure argon and in the presence of reductants (hydrogen and carbon) are proposed.     

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.     

Laser-excited atomic-fluorescence spectrometry with electrothermal tube atomization

The performance of graphite-tube electrothermal atomizers is evaluated for laser-excited atomic-fluorescence spectrometry for several elements. Three pulsed laser systems are used to pump tunable dye lasers which subsequently are used to excite Pb, Ga, In, Fe, Ir, and Tl atoms in the hot graphite tube. The dye laser systems used are pumped by nitrogen, copper vapour and Nd:YAG lasers. Detection limits in the femtogram and subfemtogram range are typically obtained for all elements. A commercial graphite-tube furnace is important for the successful utilization of the laser-based method when the determination of trace elements is intended, especially when complicated matrices may be present.     

Periodic trends in sensitivity and its dependence on the properties of pyrolytic and non-pyrolytic graphite in graphite-furnace atomic-absorption spectrometry

The sensitivities for metal determination by GFAAS in the peak-height and integration modes were examined with pyrolytic graphite (PG) and non-pyrolytic graphite (NPG) tubes for 34 elements. It was found that there are periodic trends of the mole sensitivity and the elements can be classified according to whether their sensitivity of determination is enhanced by use of (a) the PG tube (alkali, alkaline-earth and transition metals); (b) the NPG tube (semi-metals); about equally by both tubes (Mg, Zn, Cd, and Pb). The mole sensitivity pM for atomic-absorption spectrometry (AAS) was defined as pM = -log(m(h)/A(w)) where m(h) is the weight of an element corresponding to 1% absorption and A(w) is the atomic weight. It was found that the pM values for graphite furnace AAS have a periodic trend similar to that for flame AAS and atomic-fluorescence spectrometry.