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Anal. Chem. 1985, 5 7 , 21-25
As ion fractions become smaller (Le., in groups ZA, 3B, etc.) measuring ion fractions precisely becomes more difficult. The LEI results presented in the previous sections suggest that LEI may be more sensitive to changes in the ion concentration in the flame than traditional techniques, employing atomic absorption (14) and ionic emission (28). The relative ion fraction could be calculated for any element, M, by choosing a reference element and assigning it an ion fraction of 1i.e., Iref= 1. Experimental LEI measurements of Crepand CMowould provide the necessary data for the calculation. If the Saha value for the reference element was used instead of 1,the calculated relative ion fraction would approximate the absolute value. Current and LEI measurements indicated that relative ion fraction measurements are valid only when elements of similar cross-sectional area and/or mobilities were determined. A more general equation might be derived by using additional factors such as ion mobilities and atomization efficiencies. This equation would allow the investigator to use pairs of elements without regard for size differences. The parameters involved in determining CMo(e.g., applied voltage and electrode diameter) are flexible enough so that the technique should be applicable to a wide range of ion fractions.
ACKNOWLEDGMENT Discussions with David L. Monts, David W. Paul, and Jerry D. Messman were invaluable during all phases of this work. We acknowledge the helpful comments of C. Th. J. Alkemade and N. S. Nogar.
LITERATURE CITED (1) Green, R. B.; Keller, R. A.; Schenck, P. K.; Travis, J. C.; Luther, G. G. J. Am. Chem. SOC. 1976, 98, 6517-8516. (2) Lewton, J.; Weinberg, F. J. "Electrical Aspects of Combustion"; Clarendon Press: Oxford, 1969; pp 319-322. (3) Travis, J. C.; Schenck, P. K.; Turk, G. C.; Mallard, W. G. Anal. Chem. 1979, 5 1 , 1516-1520.
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VanDlJk, C. A.; Alkemade, C. Th. Combust. Flame 1980, 38, 37-49. Green, R. 8.; Havrilla, G. J.; Trask, T. 0. Appl. Spectrosc. 1980, 3 4 , 561-569. Havrilla, G. J.; Green, R. B. Anal. Chem. 1980, 5 2 , 2376-2363. Trask, T. 0.; Green, R. 6.Anal. Chem. 1981, 5 3 , 320-324. Nippoldt, M. A.; Green, R. B. Anal. Chem. 1983, 5 5 , 554-557. Turk, G. C. Anal. Chem. 1081, 53, 1187-1190. Trask, T. 0.; Green, R. B. Spectrochim. Acta, Part 6 1980, 386, 503-517. Havrilla, G. J.; Green, R. 8 . Chem. Biomed. Environ. Instrum. 1981, 1 1 , 273-280. Vickers, G. H.; Trask, T. 0.; Park J. D.; Wisman, J. A.; Durham, B.; Green, R. B. Chem. Biomed. Environ. Instrum. 1983, 12, 269-297. Smlth, B. W.; Parsons, M. L. J. Chem. Educ. 1973, 5 0 , 679-681. Kornblum, G. R.; DeGalan, L. Spectrochim. Acta Part 6 1973, 2 8 8 , 139-147. Meshkova, S . 6.;Poluektov, N. S. Zh. Prikl. Spektosk. 1965, 2 , 21-25. Woodward, C. Spectrosc. Lett. 1971, 4 , 191-193. Alkemade, C. Th. J.; Herrmann, R. "Fundamentals of Analytical Flame Spectroscopy"; Halstead Press: New York, 1979; p 75. Robinson, J. W., Ed. "CRC Handbook of Spectroscopy", CRC Press: Baca. Raton, FL, 1974; Vol. 1, p 614. Shannon, R. D. Acta Crystallogr. Sect. A 1976, A32, 751. Rostas, F., International Symposium on MHD Electrical Power Generation, ENEA, Parls, 1964, p 91. Zlmin, N., Internatlonal Symposium on Electrical Power Generation, ENEA, Paris, 1964, p 316. Harris, L. R., General Electric Research Laboratory Report No. 63-RL3334G, 1963. Lawton, J.; Weinberg, F. J. "Electrical Aspects of Combustion"; Clarendon Press: Oxford, 1969; p 122. Sal'sedo Torres, L. E.; Zorov, N. B.; Kuzyakov, Yu. Ya.; Matveev, 0. I . Vestn. Mosk. Univ. Ser. 2 : Khim. 1962, 2 3 , 474-476. Sanui, H.; Pace, N. Anal. Biochern. 1988, 2 5 , 330-346. Foster, W. H.,Jr.; Hume, D. N. Anal. Chem. 1959, 3 1 , 2033. Willis, J. 6."Analytical Flame Spectroscopy"; Mavrodineanu, R., Ed.; MacMillan: London, 1970; pp 555-556. Manning, D. C.; Capacho-Delgado, L. Anal. Chim. Acta 1966, 36, 312-3 16.
RECEIVED for review June 11,1984. Accepted September 24, 1984. This work was supported by the National Science Foundation and was presented in part at the 17th Midwest Regional American Chemical Society Meeting, Columbia, MO, Nov 1981.
Sensitivity Enhancements for Flow Injection Analysis-Inductively Coupled Plasma Atomic Emission Spectrometry Using an On-Line Preconcentrating Ion-Exchange Column Steven D. Hartenstein, Jaromir RuiiEka,' and Gary D. Christian* Department of Chemistry, University of Washington, Seattle, Washington 98195 A method utlllrlng a mlnlature lon-exchange column of Chelex 100 has been developed to Increase the sensltlvlty for multlelement measurements by lnductlvely coupled plasma atomlc emlsslon spectrometry (ICP-AES). Separate buffered samples (pH 9) are pumped through two parallel columns, for doubled sampllng frequency, at 9.5 mL/mln and sequentlally eluted dlrectly to the nebulizer of the ICP by using a flow inlectlon analysis (FIA) system. This FIA-ICP method glves slmultaneous multlelement detection llmits which are over 20 tlmes better than for conventlonal contlnuously asplrated systems for barlum, berylllum, cadmium, cobalt, copper, manganese, nickel, and lead. Preclslon of the technique Is better than 6 % RSD at the 10 ppb level for aqueous standards, and the sampllng rate is 30 samples/h. Present address: Chemistry Department A, T h e Technical University of Denmark, Building 207, DK-2800 Lyngby, Denmark. 0003-2700/85/0357-0021$01 S O / O
Flow injection analysis (FIA) has increasingly been applied as a means of sample introduction for inductively coupled plasma atomic emission spectrometry (ICP-AES) (1-5). FIA-ICP systems for small volumes have been shown to be reproducible, rapid, and economical but generally have led to poorer detection limits when compared to those for conventional continuous aspiration. Therefore, a modification in the nebulizer design utilizing a microconcentric nebulizer has been designed to make FIA-ICP detection limits comparable to those achieved by conventional continuous sample aspiration (4). To improve detection for FIA-ICP, Greenfield (3) contemplated using FIA to preconcentrate samples by either solvent extraction or ion exchange. In related areas of flame atomic absorption (FAA), Olsen et al. (6),using a microcolumn of Chelex 100 in an on-line FIA-FAA system, achieved 20-fold preconcentration of heavy metals in seawater in demonstrating the Potential Of this new technique. On the 0 1964 American Chemical Society
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ANALYTICAL CHEMISTRY, VOL. 57, NO. 1, JANUARY 1985
Table I. Operating Conditions for ICP coolant argon flow rate plasma argon flow rate sample argon flow rate rf incident power rf reflected power nebulizer observation height above load coil
20 L/min
