Some Applications of Spectral Overlap in Atomic Absorption Spectrometry J.
D. Norris and T. S. West
Chemistry Department, lmperial College of Science and Technology, London SW7 2 A Y , England
Several potential spectral overlaps between the emission profile’ of the line source of one element and the absorption profile of another were investigated in atomic absorption, and eleven found giving sensitivities better than 250 ppm. The cases found show that spectral overlaps can occur when the separation of the emission line and the absorption line wavelengths is as great as 0.05 nm. It was not found possible to utilize any of these spectral overlaps for the stimulation of atomic fluorescence. The lead-palladium and antimony-lead spectral overlaps were studied in greater detail, including the determination of lead in copper-base alloys using the antimony-lead overlap.
Eighteen instances of the overlap of the spectral lines of different pairs of elements have been reported in the literature for atomic absorption spectrometry ( I - 1 1 ) , and these are listed in Table I. This phenomenon suggests that atomic emission and absorption line profiles may be considerably broader than has frequently been suggested. Some of these spectral overlaps, when both the emission and absorption lines are resonance lines, serve to explain observed atomic absorption interference effects. However, in a few of those cases ( I , 5-7, 9 ) , when the emission line is a non-resonance line, a sufficient atomic absorption sensitivity has been reported by means of the spectral overlap, for it to be of some potential analytical use. Three of the spectral overlaps included in Table I, ciz., arsenic-cadmium, iodine-bismuth and neon-chromium, (In all references to spectral overlaps, the emitting element is given first and the absorbing element second.) have also been successfully used to stimulate atomic fluorescence (7, 9, 10, 12, 13). In addition, five other spectral overlaps have been reported in atomic fluorescence, using mercury and cadmium spectral sources (14). Considerable attention has recently been given to the application of atomic absorption and atomic fluorescence spectrometry to the analysis of major components of a vaC. W . Frank. W . G . Schrenk, and C. E. Meloan, Anal. Chem.. 38, 1005 (1 966) V . A. Fassel, J. A. Rasmuson, and T. G . Cowley, Spectrochim. Acta. Part E . 23,579 (1968). J. E. Allan, Spectrochim. Acta. Part 6. 24,13 (1969). D. C. Manning and F . Fernandez, A t . Absorption Newsleft., 7 , 24 (1968). K. C. Thompson, Analyst, (London). 9 5 , 1043 (1970). D. C. Manning, At. Absorption Newsleft., IO. 97 (1971). J. D. Norris and T. S. West, Anal. Chem., 45. 2148 (1973). S. Slavin and T. W . Sattur. A t . Absorption Newslett.. 7, 99 (1968). R. M . Dagnall. K . C. Thompson, and T. S. West, Talanta. 14, 1467 (1967). A. Fulton, K. C. Thompson, and T. S. West, Anal. Chim. Acta. 51, 373 (1970). W . R . Kelly and C. B. Moore, Anal. Chem., 45, 1274 (1973). R. S. Hobbs, G . F. Kirkbright. and T. S. West, Talanta. 18, 859 ( 1971). J. F. Alder and T. S. West, Anal. Chim. Acta. 51, 365 (1970). N. Ornenetto and G . Rossi. Anai. Chim. Acta. 40, 195 (1968).
riety of technical materials. Spectral overlap has advantages in such determinations, since the lower sensitivity obviates the necessity for large dilutions. Current investigations of simultaneous and rapid-sequential multi-element atomic spectrometric systems of analysis also suggest possible future analytical uses for spectral overlaps. The purpose of the present investigation was to look for additional potentially useful incidences of spectral overlap, in atomic absorption and atomic fluorescence spectrometry, including further studies of some of those which had previously been suggested or reported. Eleven new instances of spectral overlap are reported for atomic absorption. The application of one of the spectral overlaps investigated for the determination of lead in metal alloys, using an antimony hollow cathode lamp as the spectral source, is also described.
EXPERIMENTAL Apparatus. A Techtron AA4 atomic absorption spectrometer was employed for all determinations. The spectral sources used were hollow cathode lamps (either conventional or auxiliary electrode type), except for the mercury source, which was a microwave excited electrodeless discharge lamp. For atomic absorption, a nitrous oxide-acetylene flame was supported on a 5-cm path burner, while a 10-cm path burner was used for air-acetylene and air-hydrogen flames. For atomic fluorescence, a circular separating burner was used with a n argon-separated air-acetylene flame. Reagents. CP grade reagents were employed throughout this work. General Procedure. The general procedure for examining spectral overlaps in atomic absorption was a s follows. The flame giving the best sensitivity reported in the literature for the element to be determined by conventional atomic absorption was selected. A fairly concentrated standard solution of the element was nebulized into this flame, and the main parameters of fuel and oxidant flow rates, burner height, power supply to the spectral source, wavelength setting, and monochromator slit-width were optimized to give the maximum absorbance. An analytical curve was obtained by nebulizing a series of standard solutions. The sensitivity was then calculated from the analytical curve, as the concentration of the element which would give an absorbance of 0.0044. A similar procedure was adopted for the examination of spectral overlaps in atomic fluorescence. Procedure for t h e Atomic Absorption Determination of Lead in M e t a l Alloys. A standard lead stock solution (10,000 ppm) was prepared by dissolving 1.5985 grams of lead nitrate in distilled water and diluting to 100 cm3. A series of standard solutions containing between 0 and 500 ppm of lead were prepared by diluting aliquots of this stock solution so that the final solutions contained 4 cm3 of hydrochloric acid and 1 cm3 of nitric acid for every 100 cm3 of solution. An analytical curve was obtained by nebulizing these solutions into the air-acetylene flame. using an antimony hollow cathode lamp as the spectral source. The metal alloy, 0.1-0.2 gram, was weighed into a 100 cm3 beaker and 4 cm3 of hydrochloric acid and 1 cm3 of nitric acid were added. The beaker was covered with a watch glass and warmed on a hot-plate to dissolve the alloy, in the usual manner. When all of the alloy had dissolved, the solution was diluted, filtered into a 100 cm3 volumetric flask, and diluted to volume with distilled water. This solution was nebulized into the air-acetylene flame. The concentration of the sample solution was calculated by comparison with the analytical curve.
A N A L Y T I C A L C H E M I S T R Y , V O L . 46, NO. 1 1 , SEPTEMBER 1974
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Table I. Cases of Spectral Overlap Reported for Atomic Absorption
Sourcen
Emission wavelength, nm
Iron Iron Iron Iron Iron Copper Iron Silicon Aluminium Gallium Manganese Mercury Germanium Neon Neon* Antimony Iodine* Arsenic* Zinc
324.728 327.445 285.213 352.424 279,470 324.754** 271.903** 250.690** 308.215** 403.298** 403.307** 253.652** 422.657 359.352 359.352 217.023 206,163 228.812 213.856**
Analyte
Absorption wavelength, nm
Separation, nm
Sensitivity, ppmC
Copper Copper Magnesium Nickel Manganese Europium Platinum Vanadium Vanadium Manganese Gallium Cobalt Calcium Chromium Chromium Lead Bismuth Cadmium Iron
324.754 327,396 285.213 352.454 279.482 324.753 271.904 250.690 308.211 403.307 403.298 253,649 422.673 359.349 359.349 216.999 206.170 228.802 213.859
0.026 0,049
