ANALYTICAL CHEMISTRY, VOL. 51, NO. 12, OCTOBER 1979
zones to waste. However, instead of the flow coming to a halt in column 2, the second pump maintains the flow in this column. T h e retained compounds (desired) can be detected simultaneously with flushing undesirable components from column 1. This approach is considerably faster than the arrangement in Figure 2 and is currently being used in our laboratory for several clinical assays. The only obvious disadvantage is the cost involved in dedicating a second pump to the system; however, in service laboratories the conservation of time can pay for the pump in a few days.
CONCLUSION The use of LCEC for the assay of dopamine-6-hydroxylase activity compares well to other methods and has several advantages. The simple sample work-up procedure allows up to 20 samples to be prepared in parallel in 2 h or less. Even with the addition of an internal standard, 4 and 7 samples can be analyzed per hour using the single and dual pump column switching, respectively. Another advantage to using LCEC is t h a t the same instrumentation can be used for the analysis of urinary or plasma catecholamines. A slight modification of the mobile phase is all that is required. The small diameter stainless steel tubing that connects the switching valve to the two columns adds very little band spreading. Although the assay described here has been applied only to human serum; tissue samples, CSF, and animal sera could easily be incorporated into the assay. The smaller activity found in these samples presents detection problems for most methods; however, the thin-layer amperometric detector employed in this procedure can detect less than 50 pg (0.3 pmol) of norepinephrine injected while maintaining sufficient precision and accuracy.
LITERATURE CITED (1) Axelrod, J. Pharmacol. Rev. 1972, 24, 233-43. (2) Weinshilboum, R. M.; Thoa, N. B.;Johnson, D. G.; Kopin, I. J.; Axelrod, J. Science 1971, 174, 1349-51. (3) Algate, D. R.; Leach, G. D. H. J . Pharm. Pharmacol. 1978, 30, 162-66.
1965
(4) Ngai, S. H.; Dairman, W.; Marchelle, M.; Spector, S. Life Sci. 1974, 14, 2431-39. (5) Aberg, H. E.; Hansson, H. E.; Wetterberg, L.; Ross, S. B.; Frcden, 0. Life Sci. 1974, 14, 65-71. (6) Schanberg, S. M.; Kirshner, N. Biochem. Pharmacol. 1976, 25, 617-21. (7) Alexander, N.; McChskey, J.; Maronde. R. F. Life Scl. 1976, 18, 655-62. (8) Planz, G.;Wiethold, G.; Appel. E.; Bohmer, D.; Palm, D.; Grobecker, H. Eur. J . Clin. Pharmacol. 1975, 8, 181-88. (9) Nagatsu, T.; Kato, T.; Numata, Y . (Sudo); Ikuta, K.; Sano, M.; Nagatsu, I.; Takeuchi, T.; Matsuzaki, M.; Umezawa, H. &@entia 1977, 33, 581-83. (10) Lake, C. R.; Ziegler, M. G.; Coleman, M.; Kopin, I. J. Circ. Res. 1977, 41, 865-69. (11) Horwitz, D.; Alexander, R. W.; Lovenberg, W.; Keiser, H. R. Circ. Res. 1973, 32, 594-99. (12) DeQuatlro, V.; Campese, V.; Lurvey, A.; Yen, G.; Kypridakis, G. Biochem. Med. 1976, 15, 1-9. (13) Horwitz, L. D.; Travis, V. L. J . Ciin. Invest. 1978, 62, 899-906. (14) Fujita, K.; Ito, T.; Maruta, K.; Teradaira. R.; Beppu, H.; Nakagami, Y.; Kato, Y.; Nagatsu, T.; Kato, T. J . Neurochem. 1978, 30, 1569-72. (15) Okada, T.; Ohta, T.; Shinoda, T.; Kato, T.; Ikuta, K.; Nagatsu, T. Neuropsychobiology 1976, 2 . 139-44. (16) Van Cauter, E.; Mendlewicz, J. Life Sci. 1978, 22, 147-55. (17) Lake, C. R.; Ziegler, M. G. Science 1977, 196, 905-06. (18) Laduron, P. Biochem. Pharmacol. 1975, 24, 557-62. (19) Felice, L. J.; Felice, J. D.; Kissinger, P. T. J . Neurochem. 1976, 31, 146 1-65. (20) Shoup, R. E.; Kissinger, P. T. Clin. Chem. ( Winston-Salem, N.C.)1977, 23, 1266-74. (21) Riggin, R. M.; Kissinger, P. T. Anal. Chem. 1977, 49, 2109-11. (22) Felice, L. J., Kissinger, P. T. Clin. Chim. Acta 1977, 76, 317-20. (23) Hallman, H.; Farnebo, L. 0.; Hamberger. B.; Jonsson, G.Life Sci. 1978, 23, 1049-52. (24) Blank, C. L.; Pike, R. Life Sci. 1976, 18, 859-66. (25) Borchardt, R. T.; Hegazi, M. F.; Schowen, R. L. J . Chromatogr. 1978, 152, 255-59. (26) Shoup, R. E.; Davis, G. C.; Kissinger, P. T., unpublished results. (27) Nagatsu, T.; Udenfriend. S. Clin. Chem. ( Winston-Salem, N.C.) 1972, 18, 980-83. (28) Kato, T.; Wakui, Y.; Nagatsu, T.; Ohnishi, T. Biochem. Pharmacol. 1976, 27, 829-31. (29) Frigon, R. P.; Converse, J. L.; Stone, R. A. Blochem. Med. 1978, 19, 1-15. (30) Fujita, K.; Maruta, K.; Teradaira, R.; Beppu, H.; Ikegame, M.; Nagatsu, T.; Kato, T. Clin. Chem. (Winston-Salem, N.C.) 1977, 23, 1947-48. (31) Kissinger, P. T.; Bruntlett, C. S.; Davis, G. C.; Felice, L. J.; Riggin, R . M.; Shoup, R. E. Clin. Chem. (Winston-Salem, N.C.) 1977, 23, 1449-55.
RECEIVEDfor review April 27, 1979. Accepted June 26, 1979. This work was supported by grants from the National Institute of General Medical Sciences and the National Science Foundation.
Simultaneous Determination of Metals in Oil by Inductively Coupled Plasma Emission Spectrometry R. N. Merryfield” and R. C. Loyd Phillips Petroleum Company, Bartlesville, Oklahoma 74004
The inductively coupled plasma in combination with a direct reading spectrometer has been used for the simultaneous determination of metals in oil to the sub ppm level. The instrument analysis time of about 1 min per sample plus an efficient sample preparation scheme give the rapid results needed for the analysis of used oils for wear metals, for the characterization of crudes and feedstocks, and for monitoring of developmental processes. Instrument parameters and a simplified sample preparation technique are discussed. The few interelement interferences encountered are computer corrected, and the effects of a detergent and of an easily ionized element are found to be negliglble.
The inductively coupled plasma, when combined with a direct reading simultaneous multichannel spectrometer, is an 0003-2700/79/0351-1965$01.00/0
excellent technique for the rapid determination of metals in oils. A specific application is the analysis of used lubricating oils to indicate potential failure in internal combustion engines. Another important application is the analysis of various refinery feed stocks that may contain certain metals that alter the conversion and product distribution during the refining process by acting as a catalyst poison. In our laboratory, plasma spectroscopy was especially helpful in the development of the proprietary “Phillips Rerefined Oil Process” for rerefining used lubricating oil. It is expected t h a t plasma spectroscopy analysis of oils will find still further applications in exploration activities and in environmental control moblems. Many articles have been published on establishing optimum operating conditions for the inductively coupled plasma and on the characterization and profiling of the plasma itself (1-7). Most of the literature deals with the application of the ICP C 1979 American Chemical Society
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ANALYTICAL CHEMISTRY, VOL. 51, NO. 12, OCTOBER 1979
Table I. Instrument Specifications focal length grating ruling primary slit secondary slit wavelength coverage
Table 111. Interferences
l m 1080 lines/mm 1 2 pm 50 p m 3400 to 8200 A
spectral lines, A
Al (I)= Ag (1) B (1) Ba (11) Ca (1) (3 (11) c u (1) Fe (11) K (1) Mg (11) Mn (11)
3961.5 3280.7 2497.7 4554.0 3158.9 2677.2 3247.5 2599.4 7664.9 2795.5 2576.1
Mo (11) Na (I) Ni (11) p (1) Pb (11) Si ( I ) Sn (11) Ti (11) v (11) Zn (1)
2816.2 5889.9 2316.0 2136.2 2203.5 2881.6 1899.9 337 2.8 3102.2 2138.6
a (I), line classified as emitted by normal atom. (11), line classified as emitted by singly ionized atom.
Table 11. Operating Parameters forward incident power reflected power argon plasma gas argon carrier gas solution uptake rate integration time observation height above load coil
1700 W
