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Anal. Chem. 1986, 58, 1269-1272 (21) Rabensteln, D. L. J . Blochem. Blophys. Methods 1984, 9 , 277-306.
RECEIVED for review June 6, 1985. Accepted November 25, 1985. This research was supported by an operating grant to D.L.R. from the Natural Sciences and Engineering Research
I
Council of Canada and by the University of Alberta. An I. W. Killam Scholarship to R.S.R., an Alberta Heritage Foundation for Medical Research scholarship to K.S.T., and an AHFMR postdoctoral fellowship to A.P.A. are gratefully acknowledged.
Ion Mobility Spectrometry/Mass Spectrometry of Some Prescription and Illicit Drugs A. H. Lawrence Unsteady Aerodynamics Laboratory, National Aeronautical Establishment, National Research Council of Canada, Ottawa, Ontario, Canada K1A OR6 Ion mobility spectrometry (IMS), also known as plasma chromatography, is an analytical technique that distinguishes ionic species on the basis of the differences in the drift velocity through a gas under an applied electrostatic field (1). It is a sensitive technique for detection of trace organics under atmospheric pressure conditions. Experimental results are usually reported in terms of ion mobility reduced to standard temperature and pressure KO (cm2 V-l s-'). The IMS has been commercially available for about 10 years but has received moderate attention as an analytical laboratory tool. Recently, however, there has been renewed interest in IMS as evidenced by the number of publications in the scientific literature (2-9). Moreover, the instrument meets a wide range of performance and operational requirements-good sensitivity, fast response time, operation at atmospheric pressure-and is rapidly gaining acceptance as a field instrument ( 1 0 , I I ) . Work is in progress in this laboratory to develop IMS-based technology, specifically designed for law enforcement and forensic field applications. We have recently reported on the application of surface sampling and IMS analysis to the detection of organonitrate explosives and drug residues. These studies addressed the effect of matrix and potential interfering chemicals on the discrimination and detection capability of the IMS (12,13). As well, in these investigations, reduced mobilities (KO) were used as the qualitative measurement of specific ions; however, a more direct identification method and the obvious way to assign masses to ions giving particular mobility peaks is to interface the IMS with a quadrupole mass spectrometer (MS). The present paper describes the identification of the primary ions associated with the mobility peaks of several prescription and illicit drugs using ion mobility spectrometry/mass spectrometry (IMS/MS).
EXPERIMENTAL SECTION Reagents. Linde high-purity air was dried by Linde molecular sieve 13X and used for both carrier and drift gases. All drugs were obtained from the reference collection of Health and Welfare Canada and were used without further purification. Samples of amphetamine, methamphetamine, methylenedioxyamphetamine, and N-acetylamphetamine were prepared as lo4 g/mL solutions in ether. The remainder of the drugs were prepared as g/mL solutions in methanol. Apparatus. The data presented in this paper were collected with a Phemto-Chem MMS-160 IMS/MS (PCP, Inc., West Palm Beach, FL). The instrument has been described elsewhere (14). The experimental parameters used to operate the IMS/MS are tabulated in Table I. Total ion mobility spectra were obtained by gating grid G2with grid GI held continuously open; the IMS electrometer detector is used to obtain mobility data, and the quadrupole mass filter is not used. Mass-identified ion mobility spectra were obtained by 0003-2700/86/0358-1269$01.50/0
Table I. Experimental Conditions parameter
value
Ion Mobility Spectrometer drift length (between grid G2and IMS collector) drift voltage carrier gas (purified air) drift gas (purified air) inlet temperature drift temperature pressure dwell time gate width delay timea digitizer resolution
5cm
.
+2800 V 100 cm3/min 500 cm3/min 210 OC 220 OC atmosphere 20 gslchannel 0.2 ms 1.28 ms 9 bits
Mass Spectrometer pressure resolution scanning speed sensitivity
9.5 x torr 850 (range 0-1000) 1000 amu/s 200 x lo2
"Time between gate opening and start of data collection.
operating the instrument with the grid gating procedure described above and with the mass spectrometer tuned to a specific m l t value. Since the detector sees only one ionic species, the mobility spectrum consists of only that peak corresponding to the ion. Furthermore, the drift time is slightly longer than that observed with the previous mode, since the ion lens and the orifice interfacing of the mass spectrometer added extra length to the drift space. Finally, mass spectral data were obtained by holding both grids G1 and G2open, allowing all the ions formed in the IMS to drift down through the tube and into the mass spectrometer. The data obtained with the Phemto-Chem MMS-160 instrument were taken by signal averaging a given number of 20-ms scans in a Nicolet signal averager (FT 1072, Nicolet Instrument, Inc.). The resulting ion mobility spectrum was displayed on an x-y recorder. All samples were introduced into the inlet of the IMS using a clean stainless steel wire; the wire was dipped in the drug solution and the solvent air evaporated prior to sample introduction.
RESULTS AND DISCUSSION The positive ion mobility spectra of all the drugs investigated, with the exception of phencyclidine, were simple with no appreciable fragments or ion clusters. The majority of compounds examined produced a single main ion peak corresponding to Mf or [MH]+ ion (Table 11) where M is the molecular species. It is well-established that, when nitrogen or air containing a little water is used as a carrier gas, positive 0 1966 American Chemical Society
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ANALYTICAL CHEMISTRY, VOL. 58, NO. 6, MAY 1986
(e 1
m/z 281
A
I
Ko=i.2i 12.4 rnsec
((d)
r c -
(C)
m/z 281
12 68 msec
t
A
A
h
A
A
I
(b)
m/z 299
n
‘qEACTANT A
A
M A
IONS
1.28
DRIFT TIME (rnsec)
22.4
Figure 1. Positive ion mobility spectra and mass-identified ion mobility spectral data for codeine (traces a-c) and acetylcodeine (traces d-f) at 220 OC.
reactant ionic species are formed; the identity and the mechanism leading to the formation of these species have been reported by several authors (1, 12). A complex series of ion/molecule reactions also occurs with many organic compounds with basic properties in the gas phase yielding [MH]+ ions via a proton transfer reaction between [H20],H+ and M; also [M - HI+, [M - CH3C02]+,and other ion fragments have been observed and attributed to complex ion/molecule chemistry occurring in the drift region of the IMS (15, 16). In the present study, the formation of protonated molecular ions was expected based on results from chemical ionization mass spectrometry (CIMS) for amines (17)and from previous IMS investigation of alkyl amines (18). The observation of the M+ ion as opposed to the [MH]+ ion (for example in the case of methylenedioxyamphetamine,Table 11) may be explained as a concentration effect. In IMS, low concentrations of sample react primarily with the [H20],H+ reactant ions to form [MH]+ product ions. More importantly, high concentrations of sample can react with N2+and N4+precursor ions to form M+ product ions (19). A detailed study of the effect of sample cohcentration on ion formation is beyond the scope of this qualitative investigation. Mass-identified ion mobility spectral data have shown that, in the case of triazolam and methylprylon,the ion mobility peak at KO= 1.13 and 1.52 cm2 V-l s-l, respectively, is a mixture of [MH]+and [M - HI+ ions. The positive ion mobility spectrum of codeine is presented in Figure la. It is a poorly resolved spectrum because of the overlap of two ion mobility peaks with reduced mobilities of 1.18 and 1.21 cm2 V-l s-l. According to the mass-identified mobility spectra shown in Figure 1 (b and e), the two ions contributing to the broad unsymmetrical IMS peak are m / z 299 and 281 corresponding to M+ and [M - H20]+,respec-
‘ . I .20
-M
7 -
1.16
0
D >
N
-5
1.12’
0
Y
1.08
t
i 0
h
“04
\ I 2
T
80 A
I .oo2.40
MORPHINE: R=R’=H CODEINE: R C H 3 ; R‘=H THEBAINE: R=R’-CH3 06-MONOACETYLMORPHINE: R=H; R’=COCHs ACETYLCODEINE: R-CHQ; R‘=COCH3 HEROIN: R=R’=COCH, CORR. 2.44 COEFF: 0.9835 2.48 2.52 2.56
2
0
LOG MOLECULAR WEIGHT
Figure 2. Relationship of reduced mobility and molecular weight for the opiate series.
tively. Morphine exhibits similar dehydration behavior to codeine and produces two unresolved mobility peaks with reduced mobilities of 1.22 and 1.26 cm2V-l s-l corresponding to M+ and [M - HzO]+,respectively. Acetylcodeine, 06-monoacetylmorphine,and heroin showed similar fragmentation pattern with production of two major well-resolved ion mobility peaks corresponding to M+ and [M
ANALYTICAL CHEMISTRY, VOL. 58, NO. 6, MAY 1986
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Table 11. Reduced Mobility Values in Air compd
MW
diazepam triazolam methyprylon AB-tetrahydrocannabinol cannabinol amphetamine methamphetamine N-acetylamphetamine thebaineb codeine
284.8 342.8 183 314 310 135 149 177 179 311 299
morphineC
285
acetylcodeine
341
OB-monoacetylmorphineb
327
heroin
369
phencyclidineb
243
methylenedioxyamphetamine
KO,cm2V-'
s-l
1.21 1.13 1.52 1.05 (1.06)a 1.06 1.66 1.63 1.53 1.49 1.14 1.18 1.21 1.22 1.26 1.09 1.21 1.13 1.26 1.04 (1.0f~)~ 1.14 (1.14)d 1.27 1.63 2.01 2.23
ion mass, amu 284, 286 342, 344 182,184 314 310 136 150 178 179 311 299 281 285 267 341 281 327, 325 267 369 310 243 159 86 80
ionic formula [MI'
[M - HI+, [MH]+
[M - HI', [MH]+
[MI+ [MI+ [MHI+ [MHI+ [MHI+ [MI+ [MI+ [MI+ [M - HzO]' [MI+
[M - HZO]' [MI+ [M - CH3C021' [MI+,[M - Hzl' [M - CH3C02]+ [MI+ ' [M - CH3C021' [MI [ 1-phenylcyclohexene]H+ [piperidine]H+ [pyridine]H+ +
Reference 15. Drum are in the hydrochloride salt form. Drug is in the sulfate salt form. Reference 16.
K O = 1.63
K0=2.01 7.48 msec
KO: 1.27
KO= 2 . 2 3 20 SECONDS
I
I
I
1.28
DRIFT TIME
I
(msec)
I
22.4
Figure 3. Positive ion mobllity spectra of phencyclidine hydrochloride as a function of time at 220 OC.
- CH&02]+ (Figure Id-f and Table 11). For the opiate series,
the reduced mobility of the molecular ion decreased with increasing molecular weight (MW), and the relationship between KOand MW was found to be
KO = 5.05 - 1.56 log MW
(1)
A slight decrease of 0.04 in mobility is consistent with an increase in mass and cross-sectional collision area arising from
the addition of a methyl group in codeine compared to morphine and in thebaine compared to codeine. Similarly, a decrease of 0.09 in the reduced mobility of 06-monoacetylmorphine compared to morphine and of heroin compared to 06-monoacetylmorphine is consistent with the addition of the acetyl group (Figure 2). Phencylidine wag introduced in the inlet of the IMS as the hydrochloride salt (PCP.HC1) and gave a complex ion mobility
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Anal. Chem. 1986, 58, 1272-1273
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-preventive agent (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
0003-2700/86/0358-1272$01.50/00 1986 American Chemical Society
