Anal. Chem. 1990, 62, 857-864 (15) Layman, L. R.; Hieftje, G. M. Anal. Chem. 1975, 4 7 , 194. (16) Estes, S.A.; M e n , P. C.; Barnes, R. M. Anal. Chem. 1981, 53, 1336. (17) Quimby, B. D.; Sullivan, J. J. Paper S7 presented at the 1988 Winter Conference on Plasma Spectrochemistry, San Diego, CA, Jan 3-9, 1988. (18) Rkby, T. H.; Talmi. Y. CRC Crit. Rev. Anal. Chem. 1983, 14, 231. (19) Estes. S.A.; M e n , P. C.; Barnes, R. M. Anal. Chem. 1981, 53, 1829. (20) Rice, G. W.; D'Silva, A. P.; Fassei, v. A. Spectrochjm, Acta 1985, 408. 1573. (21) McAteer, P. J.: Ryerson, T. B.: Argentine, M. D.: Ware, M. L.; Rice, G. W. Appl. Spectrosc. 1988, 4 2 , 588.
(22) Ware, M. L. Masters Thesis, College of William and Mary, Aug 1988. (23) Grob K.: Grob, G. J . Chromatogr. 1974, 90, 303. (24) Murray, A. J.: Riley, J. P. Anal. Chim. Acta 1974, 65, 261. 1974, (25) Bellar. T. A,; Lichtenburg, J. J. J . A m , water works 703.
857
(26) Quimby. B. D.; Delaney, M. F.; Uden, P. C.; Barnes, R . M. Anal. Chem. 1980, 52, 259. (27) Goldberg, M. C.;DeLong, L.; Sinclair, M. Anal. Chem. 1973, 45, 89. (28) Grob. K.: Grob, K., Jr.; Grob, G. J . Chromatogr. 1975, 106, 299.
RECEIVED for review August 28, 1989. Revised manuscript received January 9,1990. Accepted January 12,1990. The authors gratefully acknowledge financial support for this research from the Thomas F. and Kate M. Jeffress Memorial Trust. This work was presented in part at the 1989 Federation 0fAnalyticd and S P ~ C ~ ~ O ~Societies C O P Y Conference, October 1-6, 1989, Chicago, IL.
Minimization of Interferences in Inductively Coupled Plasma Mass Spectrometry Using On-Line Preconcentration E. M. Heithmar* and T. A. Hinners U S . Environmental Protection Agency, P.O. Box 93478, Las Vegas, Nevada 89193-3478 J. T. Rowan Lockheed Engineering and Sciences Company, 1050 East Flamingo Road, Las Vegas, Nevada 89119
J. M. Riviello Dionex Corporation, 1228 Titan W a y , P.O. Box 3603, Sunnyvale, California 94088-3603
A semiautomated system Is used to preconcentrate Ti, V, Mn, Fe, Co, NI, Cu, Cd, and Pb, In order to remove high salt matrices. The preconcentratlon system accepts digests with actd concentrationsequlvalent to 0.8-1.4 % HNOS,neutralizes them, and loads them onto a macroporous lmlnodlacetate resln. The alkali and alkaline-earth metals, along with deleterlous anions such as chloride, are washed off the resln before and analyte metals are eluted with nitric acld. A total of 13 Isotopes of the analytes are measured. An examlnatbn of the apparent concentratlon efflclencles, as well as the behavior of two Internal standard elements added to the eluate stream, lndlcates that the elution front matrix enhances the lnductlvely coupled plasma mass spectrometry response of the analytes. Investlgatlon of the nature of the blaqk signals suggests that the detection limits of several of the lsotopes could benefit by much larger preconcentratlonfactors, while those of vanadlum, copper, cadmium, and lead are currently llmlted by reagent purity and laboratory contamlnatlon. The preconcentratlon system Is evaluated on several slmple synthetic matrices, as well as on synthetic seawater and three wastewaters. Dlgestlon of samples contalnlng natural organic chelators is required.
The analysis of environmental samples for trace elements poses two major problems. First, regulatory action-levels for environmental concentrations of many metals are in low part-per-billion level. In order to ensure that "false-negatives" are not caused by slight variations in method performance, it is desirable to have detection limits a t least 10-fold lower than these levels. Second, the matrices encountered in environmental samples are diverse and often complex. Because
of the need for low detection limits, graphite furnace atomic absorption spectrometry (GFAAS) and, more recently, inductively coupled plasma mass spectrometry (ICP-MS) have been employed in environmental analysis (1,Z). ICP-MS has the advantage over GFAAS of being a multielemental technique, but it has not yet been accepted for analyses related to regulatory compliance. One of the major drawbacks of ICP-MS, compared to such robust techniques as inductively coupled plasma atomic emission spectrometry (ICP-AES), is the interferences often exhibited with the complex matrices encountered in environmental analysis. These interferences can be spectral (2, 3),or physicochemical (4,5),in nature. The former have been treated mathematically, by the use of various fundamental or empirical correction terms in the calibration function. The physicochemical effects can be ameliorated to a certain extent by the use of internal standardization (4) or alternative sample introduction techniques, such as flow injection analysis (5). All of these approaches decrease the signal-to-noise ratio to some extent, and none of them is completely adequate for complex matrices. Preconcentration can be used to separate analytes from interferences prior to analysis. The analytes are generally complexed with some chelating agent. Separation can be effected by solvent extraction (7), precipitation (8),or the use of an immobilized form of the chelating agent, such as with a resin. The last approach has become increasingly popular in the last few years. The resin can be digested to liberate the trace elements (9) or the analytes can be released by changing the ionic form of the resin. The latter method allows semiautomated methods to be developed that make use of resin-packed columns. Many such methods have been described (10-1 7). Although some methods have employed chelating agent adsorbed on hydrophobic resins (IO),acidic
0003-2700/90/0362-0857$02.50/00 1990 American Chemical Society
858
ANALYTICAL CHEMISTRY, VOL. 62, NO. 8, APRIL 15, 1990
Table I. ICP-MS Conditions torch: normal "short" type gas flows: plasma, 12 L/min; auxiliary, 1.8 L/min; nebulizer, 1.1 L/min
1MHN03
i o r 3 mumin
'
,'
'//'
foreward power: 1200 W reflected power:
