1185 zyxwvutsrqp Anal. Chem. 1990, 62, 1185-1193 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHG of the zyxwvutsrq “U” tube densitometer used in this work and for helpful discussion. We also thank Dr. Scott Boyette, also from the University of Delaware, for modifying the densitometer for high-pressure work. Registry zyxwvutsrqp No. MeOH, 67-56-1. LITERATURE CITED (1) zyxwvutsrqponm Yonker, C. R.; McMinn, D. G.; Wright, B. W.; Smith, R. D. J. Chroma- (2) Yonker, C. R.; Smith, R. D. Anal. Chem. 1987, 59, 727-731. (3) Snyder, L. R. J. Chromatogr. 1974, 92, 223-230. (4) Rohrschnelder, L. Anal. Chem. 1973, 45, 1241. (5) Snyder. L. R. Prlnciph of Adscvptkm Chromafography; Marcel Dek- ker: New York, 1968; Chapter 8. (6) Snyder, L. R.; Klrkhnd, J. J. Introduction to Modern Liquid Chromatog- raphy, 2nd zyxwvutsrqpo ed.; John Wiley: New York, 1979. (7) Saunders, D. L. Anal. Chem. 1974, 46, 470-473. (8) Yonker, C. R.; Frye, S. L.; Kaikwarf, D. R.; Smith, R. D. J. Phys. Chem. 1986, 90, 3022-3026. 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Thesis, Brigham Young Univeristy, Provo, UT, 1986. (20) Bartle, K. D.; Leyendecker, D. In Supercrltlcel Fluid Chromatography; Smith, R. M., Ed.; The Royal Society of Chemistry: London, 1988; Chapters 1 and 3. (21) Fields, S. M.; Markdes, K. E.; Lee M. L. J. Chromatogr. 1987, 406, (22) Morin, Ph.; Caude, M.; Rosset, R. J. Chromatogr. 1987, 407, 87-108. (23) Blilie, A. L.; Greibrckk, T. Anal. Chem. 1985, 57, 2239-2242. (24) Lee, M. L.; MarkMes, K. E. HFtC C C , J. Hlgh zyxw Resolut. Chromatogr. Chromatogr. Commun. 1986, 9, 652-656. (25) Schoenmakers, P. J. In SupercNcal FluM Chromafography; Smith, R. M., Ed.; RSC Monograph Series; Royal Society of Chemistry: London 1988; Chapter 4. (26) Smith, R. D.; Udseth, H. R.; Wright, B. W. J. Chromatogr. Sci. 1985, 23. 192-199. (27) Dobbs, J. M.; Wong, J. M.; Lahiere, R. J.; Johnston, K. P. Ind. Eng. Chem. Res. 1987, 26, 56-65. (28) Peng, D.-Y.; Robinson, D. B. Ind. Eng. Chem. Fundam. 1978, 15, (29) Marshal, N. Gas Encyclopedia ; English Edition; Elsevier: Amsterdam, 1976. (30) Schoenmakers, P. J.; Rothfusz, P. E.; Verhoven. F. J. Chromatogr. 1987, 395, 91-110. (31) Bender, E. Proceedings ofthe 5th Symposium on Thermophysical propertes : American Society for Testing and Materials: Philadelphia, PA, 1970; p 227. 1 I$ 223-235. 59-64. RECEIVED for review November 17,1989. Accepted February 23, 1990. Chelation Ion Chromatography as a Method for Trace Elemental Analysis in Complex Environmental and Biological Samples Archava Siriraks and H. M. Kingston* zyxwvutsr Center for Analytical Chemistry, National Institute of Standards and Technology, Gaithersburg, Maryland 20899 J. M. Riviello Dionex Corporation, Sunnyvale, California 94086 The development and evaluatlon of a new method for the determlnatlon of trace transltion and rare-earth elements based on the comblnatlon of chelation and ion chromatogra- phy are descrlbed. The new method, chelation Ion chroma- tography (Chelatlon IC), uses a chelating column to con- centrate and separate trandtkn and rareearth elements from the zyxwvutsrqp common alkali and alkahwarth metals, as well as other matrlx components, prior to analysls by Ion chromatography. The sample fractlon from the chelating column contains only the concentrated analyte Ions, thus ellmlnatlng Interfering matrlx components from complex matrices such as seawater and dlgested biological, botanical, and geological materials. Thls comblnatlon of cheiatlon and Ion chromatography pro- vides a technique that makes posslble the determlnatlon of trace elements In complex matrices that have proven to be dlfflcult or Impossible to analyze by ion chromatography or conventional atomlc spectroscopy techniques. INTRODUCTION The accurate determination of trace elements in complex matrices continues to be one of the most challenging areas in analytical chemistry. While most analytical techniques are readily applicable to simple matrices, many may fail when applied to samples that represent complex matrices. This is often the case for quantification of trace and ultratrace ele- ments in seawater, estuarine water, brines, biological fluids, and acid-decomposed biological, botanical, and geological materials. The extremely high levels of alkali and alkaline- earth metals, halogens, phosphate, and other elemental and molecular matrix constituents in such materials, compared to the low levels of transition elements, present a formidable barrier to direct instrumental analysis of the trace element constituents. To determine trace elements in complex matrices, a sepa- ration and/or preconcentration is frequently necessary. The separation eliminates sample matrix components that may interfere with the subsequent analytical measurement(s), while preconcentration concentrates the analytes of interest from a large volume of sample. One of the most useful and fre- quently used methods employs an iminodiacetate chelating resin. Its application for concentrating trace elements from seawater without matrix elimination (1) was demonstrated almost two decades ago. It was then shown that the resin could be used, not only to preconcentrate but also to separate elements and groups of elements in seawater prior to instru- mental analysis by graphite furnace atomic absorption (GFAAS),inductively coupled plasma (ICP), or spark source 0003-2700/90/0362-1185$02.50/0 0 1990 American Chemical Society