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spectrum. Figure 3 shows the change in the ion mobility spectrum of PCP.HC1 with time at 220 "C. All ion identities were confirmed by IMS/MS and by injection of authentic samples. Twenty seconds after introducing the sample, PCP molecular ion M+ of m / z 243 produces the ion mobility peak at KO= 1.27 cm2 V-l s-l, while ions of m/z 86 (protonated piperidine) and 80 (protonated pyridine) are responsible for the ion mobility peaks at KO = 2.01 and 2.23 cm2 V-' s-l, respectively (Figure 3a). After 40 s, PCP molecular ion is no longer observable and a new mobility peak of KO= 1.63 cm2 V-' s-l corresponding to an ion of mass m / z 159 (protonated 1-phenylcyclohexene) is observed; the ions of m / z 86 and 80 are of equal intensity (Figure 3b). After 1 min, the relative intensities of the piperidine and pyridine peaks alternate, and eventually the pyridinium ion becomes the predominant ion as traced in Figure 3d. At 220 "C, piperidine hydrochloride exhibited similar fragmentation and mobility behavior to that shown in Figure 3, with the absence of ions of m / z 243 and 159, while pyridine gave a single ion peak at KO= 2.23 cm2 V-' corresponding to an ion with mass m/z 80. The thermal decomposition of PCPaHCl, under various gas chromatographic conditions, to 1-phenylcyclohexeneand piperidine has been reported by Legault (20). k the temperature of the IMS was decreased, less decomposition was observed, and at 190 O C , PCP.HC1 gave a single ion peak of KO= 1.27 cm2 V-I s-l corresponding to PCP molecular ion.
CONCLUSION The IMS is easily capable of resolving the molecular ion species of the drugs investigated and can be used for the fingerprint identification of these compounds. In some cases, two ion peaks are produced due to fragmentation thus enhancing the IMS signature that identifies the compounds. The analysis can be achieved in less than 20 s as opposed to several minutes required for gas or liquid chromatography; furthermore, the instrument operates at atmospheric pressure thus simplifying sample introduction and field operation. When the IMS is coupled to a mass spectrometer the technique provides a double basis for identification. In the IMS, discrimination is achieved on the basis of ion mobility, whereas in the MS discrimination is on the basis of mass. Once these reference values have been obtained, identification based on reduced mobility values is adequate for field screening pro-
cedures in law enforcement and forensic applications.
ACKNOWLEDGMENT I thank Robert M. Stimac of PCP, Inc., West Palm Beach, FL, for assistance in obtaining IMS/MS data. Registry No. Codeine, 76-57-3; 06-monoacetylmorphine, 2784-73-8;phencyclidine, 77-10-1;diazepam, 439-14-5; triazolam, 28911-01-5; methyprylon, 125-64-4; Ag-tetrahydrocannabinol, 1972-08-3;cannabinol, 521-35-7; amphetamine, 300-62-9; methamphetamine, 537-46-2;N-acetylamphetamine, 14383-60-9;methylenedioxyamphetamine, 4764-17-4; thebaine, 115-37-7;morphine, 57-27-2; acetylcodeine, 6703-27-1; heroin, 561-27-3. LITERATURE CITED (1) Carr, T. W., Ed.; "Plasma Chromatography"; Plenum: New York. 1984. (2) Spangler, G. E.; Kim, S. H. Anal. Chem. 1985, 57,567. (3) Leasure, C. S.; Eiceman. G. A. Anal. Chem. 1985, 57, 1890. (4) Knorr, F. J.; Eatherton, R. L.; S i m s , W. F.; HIii, H. H., Jr. Anal. Chem. 1985, 57,402. (5) Rokushika, S.; Hatano, H.; Balm, M. A,; Hill, H. H., Jr. Anal. Chem. 1985, 57, 1902. (6) Balm, M. A.; Hill, h. H., Jr. J . Chromafogr. 1984, 299, 309. (7) Stimac, R. M.; Cohen, M. J.; Wernlund, R. F. "Tandem Ion Mobility Spectrometer for Chemical Agent Detection, Monitoring, and Alarm", Final Report, Contract DAAKl1-84-C-0017, PCP, Inc., West Palm Beach, FL, Dec 1984. (8) Lubman, D. M. Anal. Chem. 1984, 56, 1298. (9) Proctor, C. J.; Todd, J. F. J. Anal. Chem. 1984, 56, 1794. (10) Spangler, G. E.; Caprlco, J. P.; Campbell, D. N. J . Test. Eval. 1985, 13(3), 234. (11) Blyth, D. A. Proceedings of the International Symposium on Protection against Chemical Warfare Agents, Stockholm, Sweden, June 6-9, 1983: D 65. (12) Lawreice, A. H.; Ellas, L. "United Nations Bulletin on Narcotics"; 1985; Vol. XXXVII, no. 1, 3. (13) Lawrence, A. H.; Elias, L. Proceedings of the ACS Symposium on Analytical Methods in Forensic Chemlstry, Miami, FL. ADril 29-May 2, 1985, in press. (14) Kim, S. H.; Betty, K. R.; Karasek, F. W. Anal. Chem. 1978, 50,1784. (15) Karasek, F. W.; Farasek, D. E.; Kim, S. H. J . Chromafogr. 1975, 105, 345 -
(16) Karasek, F. W.; Hill, H. H., Jr.; Kim, S. H. J. Chromafogr. 1976, 117, 327. (17) Hunt, D. F.; McEwen, C. N.; Upham, R. A.
[email protected], 47, 4539. (18) Karasek, F. W.; Kim, S. H.; Rokushika, S. Anal. Chem. 1978, 50, 2013. (19) Spangler, G. E., personal communication. (20) Legault, D. J. ChrOmatogr. Sci. 1982, 20, 228.
RECEIVED for review October 7,1985. Resubmitted December 24, 1985. Accepted January 9, 1986.
Comparison of Isotope Dilution Mass Spectrometry and Graphite Furnace Atomic Absorption Spectrometry with Zeernan Background Correction for Determination of Plasma Selenium S. A. Lewis,' N. W. Hardison, and Claude Veillon*
U S . Department of Agriculture, Room 117, Building 307, Beltsville, Maryland 20705 There has been increasing interest in the measurement of selenium in plasma because of the toxicological and nutritional importance of selenium. More recently selenium has been implicated as an anticarcinogen and a carcino-preventiveagent (1).
Several techniques are used to measure plasma selenium concentrations. One of the most popular, at present, is the use of graphite furnace atomic absorption spectrometry (2) Present address: Hazleton Biotechnology Corp., Vienna, VA.
with Zeeman background correction (ZAAS), which permits the determination of selenium in plasma with minimal sample manipulation. We dilute plasma with a matrix modifier containing Ni and Mg to thermally stabilize selenium and use a L'vov platform and peak area integration. However, we do have a t our facility the capability of validating this method using an isotope dilution mass spectrometry (IDMS) technique (3),which can be considered a definitive method. Comparison of results obtained by two independent methods that utilize different physical properties is probably the best way to verify
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Table I. Furnace Conditionsn step
ramp, s
dry ash atomize cleanout
60
cool down
hold, s
temp, "C
10
150 1000 2100b 2700 20
20
1 0 1 1
4 4
14
L'vov platform, 4-s peak area integration,X10 scale expansion bInterna1 flow = O mL/min (argon). Table 11. Day-to-Day Imprecisions of Quality Assurance Materials (Mean f Standard Deviation ( % Relative Standard Deviation)) material
IDMS, rg/L
ZAAS, rg/L
RM 8419" SRM 90gb plasma pool
16 f 2 (12.5) 106 f 2 (1.8) 112 f 3 (2.7)
16 f 4 (25.0) 108 f 4 (3.7) 112 i 7 (6.2)
a Recommended value f estimate of uncertainty: 16 * 2 pg/L, from ref 5. bNot yet certified by NBS. Certification planned at 107 & 7 ua/L based on this work.
the accuracy of a new method. Imprecisions for both methods are established by the regular use of well-characterized reference materials.
EXPERIMENTAL SECTION ZAAS. A Perkin-Elmer 5000 atomic absorption spectrometer (Perkin-Elmer Corp., Norwalk, CT) utilizing a selenium electrodeless discharge lamp (196.0 nm) with a 2.0-nm slit width and equipped with Zeeman background correction and an AS-40 autosampler was used. The graphite furnace program is shown in Table I. A base-line correction was made immediately prior to atomization. The sample and standard diluent containing the matrix modifier were prepared by dissolving 1.0 g of Ni(N03)z.6Hz0and 2.0 g of Mg(NO3)~-6H20 (Spex Industries, Metuchen, NJ) in 100 mL of 0.2% Triton X-100 (Sigma Chemical Co., St. Louis, MO). Seronorm Protein, lot 103 (Accurate Chemical & Scientific Corp., Westbury, NY), which has been reserved (for commercial distribution by Accurate) by the IUPAC Subcommittee on Selenium, with an established selenium content of 93 i 7 Mg/L, was used as the standard (4). Aliquots of 100 pL of the standard, samples, and controls were diluted with 400 & of diluent. Bovine serum Reference Material (RM) 8149 (51, human serum Standard Reference Material (SRM) 909 (National Bureau of Standards, Gaithersburg, MD), and an internal human plasma pool were utilized as quality assurance materials. Blanks were monitored; however, no measurable selenium was detected. Deionized water (Millipore Corp., Bedford, MA) was used throughout,
IDMS. The apparatus and method have been fully described elsewhere by Reamer and Veillon (3). Again bovine serum RM 8419, human serum SRM 909, and the internal human plasma pool were used as quality controls. Blanks were monitored and results corrected when necessary. RESULTS AND DISCUSSION Means and imprecisions expressed as standard deviation and percent relative standard deviation for both techniques are shown in Table 11. The IDMS method is twice as precise as the ZAAS method. Thirty human plasma samples were analyzed for selenium by both methods. Regression analysis was carried out by using the Deming method ( 6 , 7 ) ,which takes into account the error in the reference IDMS method (ordinate) as well as the error in the experimental method, in this case ZAAS. This is in contrast to conventional regression analysis, which assumes no error in the ordinate. The results obtained are as follows: R = 0.987, SE = 7.8, slope = 1-01, and intercept = -0.39. In conclusion, the ZAAS method-in our hands-compares favorably with the definitive IDMS technique but is less precise. The method is rapid and accurate and permits blood plasma and serum selenium determinations with commercially available atomic absorption instrumentation. ACKNOWLEDGMENT
S. A. Lewis was and N. W. Hardison is a Research Associate, Georgetown University Hospital, Washington, DC. Registry No. Ni, 7440-02-0; Mg, 7439-95-4; selenium, 778249-2.
LITERATURE CITED "Selenium In Biology and Medicine"; Spallholz, J.
(1)
E., Martin, J. L., Ganther, H. E., Eds.; AVI Publishing Company, Inc.: Westport, CT,
(2)
Verllnden, M.; Deelstra,
1981.
H.;
Adrlaenssens,
E. Talanta 1981, 28,
637-646. (3) (4)
(5)
Reamer, D. C.; Velllon, C. Anal. Chem. 1981, 53, 2166-2169. Ihnat, M.; Thomassen, Y.; Wolynetz, M. S.; Velllon, C., submitted for publication In Acta Pharm. Toxicol, Velllon, C.; Lewis, S.A.; Patterson, K. Y.; Wolf, W. R.; Harnly, J. M.; Versleck, J.; Vanballenberghe, L.; Cornells, R.; O'Haver, T. C. Anal.
Chem. 1985, 57, 2106-2109. E. "Statistical Adjustment of Data"; Wlley: New York, 1943. (7) Cornbleet, P. J.; Gochman, N. Clin. Chem. (Winston-Salem, N.C.) 1979, 25, 432-437. (6)
Demlng, W.
RECEIVED for review November 4, 1985. Accepted December 30,1985. This research was supported in part by the National Cancer Institute Contract Y01-CN-40620. Specific manufacturer's products mentioned herein solely reflect the personal experiences of the authors and do not constitute their endorsement nor that of the Department of Agriculture.
Preparation of Carbon Dioxide for Oxygen-18 Determination of Water by Use of a Plastic Syringe Naohiro Yoshida* and Yoshihiko Mizutani Department of Earth Sciences, Toyama University, Gofuku, Toyama 930, J a p a n The COz equilibration method (1)is used generally for the
'*Odetermination of water, but it is tedious and time-consuming (2). Although several modifications ( 3 , 4 )have already been made to reduce the time and steps required for this 0003-2700/86/0358-1273$01.50/0
conventional method, they demand expensive equipment. The present study is intended to simplify the conventional COP equilibration method by use of a plastic syringe as an equilibration vessel without decreasing its precision. 0 1986 American Chemical Society
