High Sodium Systems in Atomic Absorption Flame Photometry Juan Ramirez-Muhoz 92634
Beckman Instruments, Inc., 2500 Harbor Boulevard, Fullerton, Cal$
SODIUM IS one of the most frequent interferent concomitants in many natural samples which are analyzed by atomic absorption flame photometry. Secondary solutions prepared for instrumental measurement from those original samples generally contain fixed or variable amounts of sodium also. Because some analytes may be subject to influences by the presence of sodium ( I ) , thus producing analytical signals of different magnitude than those to be expected in the absence of sodium, a study has been made on the interference effects produced by sodium on some frequently determined analytes. This study has allowed the calculation of limiting interference ratios and the establishment of some recommendations to determine these analytes in the presence of high concentrations of sodium. (1
Table I. Limiting Interference Ratios Laminar flow burner, air-acetylene flame Hot operation Limiting interference ratio, Concentration ppm Na/ppm Analyte level, ppm analyte Potassium 1 .o lOOO/l Calcium 0.5 20/1 Magnesium 0.02 500011 0.5 5000/1= Copper 1.o 100/1 Iron Manganese 0.5 20/1 0.2 50011 Zinc Maximum ratio tested. No change of signal size was observed.
EXPERIMENTAL Instruments. A Beckman Model 979 atomic absorption spectrophotometer with laminar flow burner (air-acetylene flame) ( 2 ) and 10-inch potentiometric recorder have been used. Hollow cathode lamps were used as source, except for potassium tests, where an Osram vapor discharge lamp was utilized. Calculations. Calculations were made, when necessary, with the help of computer techniques already described elsewhere (3-5). Three-dimensional diagrams and flame profiles were also prepared by means of computer techniques. Solutions. Mixtures prepared at different analyte and concomitant concentration levels, standards, and blanks were aqueous solutions. Experimental Conditions. AnGlytical lineso used were : K 7665 A,oCa 4227 A, Mg 2852 A, Cu 3248 A, Fe 2483 A, Mn 2795 A, and Zn 2139 A. Slit width, burner elevation, lamp current, and support and fuel gas settings were adjusted to achieve maximum performance for each analyte in terms of signal size for a given concentration. RESULTS Experimental Behavior of Analytes. Each analyte was tested at sufficiently low concentration (linear portion of analytical working curves) in the presence of increasing amounts of sodium as sodium chloride. Limiting interference ratios were calculated in each case-Le., ratios concn Na/concn analyte-at which some variation of analyte signal size becomes appreciable in comparison with signals obtained with solutions containing analyte alone. Analytes, reference concentration levels, and limiting interference ratios are detailed in Table I. Limiting interference ratios given in this table are valid at low concentrations of analyte. Low concentrations are under(1) J. Ramfrez-Mufioz, “Atomic-Absorption Spectroscopy,” Elsevier Publishing Company, Amsterdam, 1968. ( 2 ) A. Hell, W. F. Ulrich, N. Shifrin, and J. Ramirez-Mufioz, Appl. Oprics, 7, 1317 (1968). (3) J. Ramirez-Mufioz, J. L. Malakoff, and C. P. Aime, Anal. Chin?. Acta, 36, 328 (1966). (4) J. L. Malakoff, J. Ramirez-Mufioz, and W. 2. Scott, ibid., 42, 515 (1968). (5) J. L. Malakoff, J. Ramirez-Mufioz, and C. P. Aime, ibid., 43, 37 (1968).
Table 11. Sensitivity Values Laminar flow burner, air-acetylene flame Hot operation ppm of analyte to produce Analyte a signal of 1 absorption Potassium 0.023 Calcium 0.013 Magnesium 0.0013 Copper 0.014 Iron 0.014 Manganese 0.0090 Zinc 0.0026
stood as a multiple less than 135 of the concentration of analyte necessary to produce a signal of 1% absorption. See Table XI. Interference Diagrams and Vertical Flame Profiles. In order to study the variation of signal size at different concentrations of analyte and at variable concentrations of sodium, three-dimensional interference diagrams were prepared by taking as measured variable absorbance values. Also, three-dimensional flame profiles (vertical flame profiles) were prepared; absorbance values were taken as a function of analyte concentration and height of the observed zone of the flame over the top of the burner; flame profiles were obtained at different sodium concentrations in solution. The first type of diagrams showed the variation of curvature in the presence of the concomitant, beside the change of signal size at high interference ratios. The second type of diagram helped to confirm the best operating height of the observed zone of the flame over the burner top, as well as variation of curvature of working curves, especially at the higher levels of the flame. Tests done with calcium and magnesium by adding sodium as sodium nitrate and sodium hydroxide, instead of sodium chloride, showed higher depressions of analyte signal size. Operation in Presence of Sodium Chloride. Sodium chloride in high concentration produces depressions of analyte signals (except in the case of copper, as mentioned in Table I), but signals are still of sufficient magnitude to be used for analytical purposes. The operation with laminar flow burners ANALYTICAL CHEMISTRY, VOL. 42, NO. 4, APRIL 1970
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with heated chambers is highly sensitive, and any decrease of signal size observed does not make analytical determinations severely difficult. Decrease of signal in the presence of high concentrations of sodium chloride can be interpreted as a consequence of (a) a change of the diffusion rate of the analyte in the flame, when transported to the flame in particles nearly dried-due to the partial evaporation of the solvent in the heated spray chamber -and (b) a shifting of the evaporation equilibria of the particles reaching the top of the burner. These circumstances decrease the efficiency of the atomization process. In the spraying process, the presence of sodium chloride in high concentration can also change the droplet size in spite of the fact that the aspiration rate was not changed, as it was experimentally tested, by comparison of aspiration rate in the absence of sodium chloride and in the presence of variable concentrations of this salt. Practically all analytes tested can be determined with the laminar flow burner, hot operation, in the presence of high concentration of sodium chloride at low interference ratios
(lower than the limiting interference ratio). These elements may be measured with the help of a series of standards without compensation. At high interference ratios (higher than the limiting interference ratios), standards should be compensated with equivalent sodium concentrations expected (or previously measured) in the samples. Whenever it is possible, samples should be diluted down t o lower concentrations. It is true that such a dilution does not change the ratio between ppm of concomitant and ppm of analyte, but by diluting the solutions the total solid content is decreased; the hot operation allows enough sensitivity to work a t lower analyte concentration ranges; and determinations can be done easily in the lower linear portions of the calibration curves; the burner is then less exposed t o deposits and clogging, and also the flame is less concentrated with respect t o entities liberated in it, resulting in better conditions to achieve the proper diffusion and evaporation equilibria.
RECEIVED for review July 30, 1969. Accepted January 19, 1970.
lodometric Determination of Tellurium(V1) in the Presence of Tellurium(IV) and Selenium(V1) Richard Beyak1 and Bruno Jaselskis Department of Chemistry, Loyola University, Chicago, Ill.
A RAPID METHOD for the determination of tellurium (VI) in the presence of tellurium(1V) and selenium(V1) has been developed. The method depends on the quantitative reduction of tellurium(V1) to tellurium(1V) by iodide ion and on the unreactivity of tellurium(1V) and selenium(V1). These species are not reduced at the experimental conditions described in our procedure. Although there are many methods and reviews of tellurium analyses reported, relatively few of these are for tellurium(V1) (1-3, especially in the presence of mixtures containing tellurium(1V) and/or selenium(V1). Tikhomirova (6) and Chavdarova and Sheytanov (7) have reported tellurium(V1) determinations in the presence of tellurium(1V). Their methods suffer the practical deficiency of requiring two determinations per sample with the amount of tellurium(V1) being obtained as the difference between a n initial tellurium(1V) assay and a total tellurium(1V) assay following the reduction of tellurium(V1) present in the sample. 1 Present address, Alberto-Culver Co., 2525 Armitage, Melrose Park, Ill. 60160
(1) G. Charlot and D. Bezier, “Quantitative Inorganic Analysis,” John Wiley and Sons, Inc., New York, N. Y., 1957. (2) T. E. Green and M. Turley in “Treatise on Analytical Chemistry,” I. M. Kolthoff, P. J. Elving, and E. B. Sandell, Eds., Part 11, Vol. 7, Interscience Publishers, New York, N. Y.,1961. (3) J. Dolezal, E. Lukshyte, V. Rybacek, and J. Zyka, CoNect. Czech. Chem. Commun., 29, 2597 (1964). (4) J. G. Lanese and B. Jaselskis, ANAL.CHEM., 35, 1878 (1963). (5) J. 0. Edwards and A. L. LaFerriere, Chemist-Analyst, 45(1), 12(1956). (6) N. P. Tikhomirova, Metody Anal. Khim. Reuctivov Prep., 12, 90 (1966). (7) R. Chavdarova and Ch. Sheytanov, Bulgarska Academia Na Naukite, Sofia, Doklady, C. R. Acud. Bulg. Sci., 20, 565 (1967). 518
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In the usual case of mixtures containing tellurium(V1) and selenium(VI), a preliminary separation procedure is required prior to the quantitative determination and the gravimetric and distillation separation procedures (8,9) are time-consuming, laborious, and subject to experimental error. The separation of selenium(V1) from tellurium(V1) in the proposed method is not necessary. However, the reduction of selenium(1V) by iodide is well established (IO), and its presence must be avoided. This paper reports the experimental conditions established for the quantitative analysis of tellurium(V1) in the presence of tellurium(1V) and selenium (VI). EXPERIMENTAL
Reagents and Materials. Telluric acid and sodium selenate were purchased from A. D. MacKay. The telluric acid was recrystallized four times before use while sodium selenate was purified by the method of Feher (11). High purity tellurium dioxide was prepared from tellurium metal (11)and the purity checked by the method of Gardels and Cornwell (12). Primary standard grade potassium iodate, for the standardization of the sodium thiosulfate, was obtained from Anachemia and vacuum dried at 80 “C for two hours. Thyodene starch indicator was purchased from Fisher Scientific Co. All other chemicals were analytical grade reagents. The dis(8) H. Bode, 2.Anal. Clzem., 144,90 (1955). 35, 139 (1963). (9) P. W. Bennett and S. Barabas, ANAL.CHEM., (10) J. S. McNulty, E. J. Center, and R. M. Macintosh, ibid., 23, 123 (1951). (11) G. Brauer, “Handbook of Inorganic Preparations,” Academic Press, New York, 1965, pp 433, 447-8. (12) M. C. Gardels and J. C. Cornwell, ANAL. CHEM.,38, 774 (1966).
