Evaluation of Opiate Separation by High-Resolution Electrospray Ionization-Ion Mobility Spectrometry/ Mass Spectrometry

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1 Anl. Chem. 2001, 73, Evlution of Opite Seprtion by High-Resolution Electrospry Ioniztion-Ion Mobility Spectrometry/ Mss Spectrometry Lur M. Mtz nd Herbert H. Hill, Jr.* Deprtment of Chemistry, Wshington Stte University, Pullmn, Wshington The seprtion of opites nd the primry metbolites ws evluted with ESI-IMS/MS. Seven opite molecules were nlyzed, nd spectr were shown for ech compound. The IMS seprtion of two isomers (morphine nd norcodeine) ws shown with bseline seprtion. Differences in the mobilities were found for the noncetylted, monocetylted, nd bicetylted compounds. In this study, two primry findings re reported. First, IMS cn esily seprte metbolic isomers, nd second, the twodimensionl seprtion cpbility of IMS/MS cn be employed to confidently identify nd seprte both the opites nd metbolites. Although previous IMS studies hve shown the seprtion of isomers, this is the first exmple to show the cpbility of IMS to seprte metbolic isomers (within 70 s), significnt dvntge in high-throughput screening for phrmcokinetic studies. Second, the monocetylted nd bicetylted compounds were found to form more compct ions for the sodium dducts in comprison to the protonted moleculr ions. On the bsis of the mobilities, informtion on structures nd conformtion cn be deduced when sodium nd protonted ions re compred. The high incidence of drug buse necessittes sensitive techniques for drug detection nd identifiction. 1 Heroin, morphine, nd codeine re the primrily bused opite compounds, lthough their metbolites re evluted s well for chrcteristic biologicl mrkers present hours fter intoxiction. 2 For this reson, opite seprtions ddress the nlysis of both the opites nd metbolites. 2,3 While mny different nlyticl techniques hve been employed for opite detection, 4-6 liquid chromtogrphy/ mss spectrometry (LC/MS) is currently the most commonly used * Corresponding uthor: (tel) (509) ; (fx) (509) ; (e-mil) hhhill@wsu.edu. (1) Sunshine, I.; Sutliff, J. P. Swet It Out. In Hndbook of Anlyticl Therpeutic Drug Monitoring nd Toxicology; Wong, S. H. Y., Sunshine, I., Eds.; CRC Press: Boc Rton, FL, (2) Blnchet, M.; Bru, G.; Guerret, M.; Bromet-Petit, M.; Bromet, N. J. Chromtogr., A 1999, 854, (3) Dienes-Ngy, A.; Rivier, L.; Giroud, C.; Augsburger, M.; Mngin, P. J. Chromtogr., A 1999, 854, (4) Goldberger, B. A.; Drwin, W. A.; Grnt, T. M.; Allen, A. C.; Cpln, Y. H.; Cone, E. J. Clin. Chem. 1993, 39, (5) Mitchell, J. M.; Pul, B. D.; Welch, P.; Cone, E. J. Anl. Toxicol. 1991, 15, (6) Osborne, R. Clin. Phrmcol. Ther., 1990, 47, method due to its bility to seprte metbolic isomers while chieving the required sensitivity with MS detection. 2,3 Since its inception, ion mobility spectrometry (IMS) hs been utilized s technique for detecting drugs of buse. 7 Until recently, IMS reserch for drug detection focused on field portble devices. 8,9 Both the coupling of electrospry ioniztion (ESI) to IMS 10 nd the introduction of high-resolution IMS instruments hve extended IMS pplictions to include more complex mixtures (drugs of buse, 14 chemicl wrfre gents, 15 nd tryptic digests 16,17 ). Current stte-of-the-rt IMS/MS systems hve chieved seprtion efficiencies comprble to common chromtogrphic techniques nd, therefore, re being evluted s high-resolution seprtion technique. 18 In IMS, ions re identified by mesuring the time it tkes the ion to trvel through drift tube. An ion s mobility cn be determined from the drift time nd is relted to n ion s size-tochrge rtio. Evlutions of high-resolution ESI-IMS/MS systems hve elucidted different gs-phse mobilities for mny peptide isomers 19 nd mino cid isomers (leucine nd isoleucine). 18 Although the reltionship between solution-phse geometry nd gs-phse geometries remins undertermined, 20 ion mobilities provide structurl informtion tht cn be utilized to consider (7) Krsek, F. W.; Hill, H. H., Jr.; Kim, S. H. J. Chromtogr. 1976, 117, (8) Fetterolf, D. D.; Donnelyy, B.; Lsswell, L. D. AT ONSITE 1996, 2 (1), (9) Fytche, L. M.; Hupe, M.; Kovr, J. B.; Pilon, P. J. Forensic Sci., 1992, 37, (10) Chen, Y. H.; Hill, H. H., Jr.; Wittmer, D. P. J. Microcolumn Sep. 1994, 6, (11) Wu, C.; Siems, W. F.; Asbury, G. R.; Hill, H. H., Jr. Anl. Chem. 1998, 70, (12) Dugourd, Ph; Hudgins, R. R.; Clemmer, D. E.; Jrrold, M. F. Rev. Sci. Instrum. 1997, 68, (13) Sreblus, C. A.; Li, J.; Mrshll, W. S.; Clemmer, D. E. Anl. Chem. 1999, 71, (14) Wu, C.; Siems, W. F.; Hill, H. H., Jr. Anl. Chem. 2000, 72, (15) Asbury, G. R.; Wu, C.; Siems, W. F.; Hill, H. H., Jr. Anl. Chim. Act 2000, 404, (16) Vlentine, S. J.; Countermn, A. E.; Hoglund, C. S.; Reilly, J. P.; Clemmer, D. E. J. Am. Soc. Mss Spectrom. 1998, 9, (17) Vlentine, S. J.; Countermn, A. E.; Clemmer, D. E. J. Am. Soc. Mss Spectrom. 1999, 10, (18) Asbury, G. R.; Hill, H. H., Jr. J. Microcolumn Sep. 2000, 12, (19) Wu, C.; Siems, W. F.; Klsmeer, J.; Hill, H. H., Jr. Anl. Chem. 2000, 72, (20) Hoglund-Hyzer, C. S.; Countermn, A. E.; Clemmer, D. E. Chem. Rev. 1999, 99, Anlyticl Chemistry, Vol. 73, No. 8, April 15, /c001147b CCC: $ Americn Chemicl Society Published on Web 03/13/2001

2 possible structures Additionl peptide structurl informtion hs been elucidted from sodium dduct formtions 24,25 in which it ws found tht doubly chrged brdykinin ions tht wrpped round sodium ion formed more compct structure thn the (M + 2H) 2+ ion. Understnding the reltionship between conformtionl geometries nd biologicl citivity is importnt for not only proteins (i.e., enzymes) but drug molecules s well. As described bove, the utility of IMS/MS for discerning peptide nd protein conformtions hs been shown. The objectives of this study were to develop IMS/MS s n lterntive (fster) seprtion technique to LC/MS. Becuse IMS provides ion size informtion, structurl fetures of the opites nd metbolites were lso investigted. EXPERIMENTAL SECTION Regents nd Chemicls. The seven opite derivtives employed in this study were purchsed from Alltech Assocites (Bellefonte, PA) s 1.0 mg/ml stndrds in methnol (heroin concentrtion ws 0.10 mg/ml) nd included normorphine, norcodeine, codeine, morphine, 6-monocetyl codeine (MAC), 6-monocetyl morphine (MAM), nd heroin. All stndrd solutions were diluted to concentrtions of 100 ppm ( 300 µm) (heroin ws diluted to 50 ppm concentrtion). All solvents (wter, methnol, nd cetic cid) were obtined from J. T.Bker (Phillipsburgh, N. J.) nd were HPLC grde. Instrumenttion. A high-resolution ESI-IMS/MS instrument ws employed for ll experiments nd hs been described previously (wter-cooled ESI source, 10 high-resolution IMS/MS, 11 nd recent modifiction to the IMS/MS 18 ). The ESI source ws mintined t 14 kv resulting in +4-kV difference between the ESI source nd the trget screen. The ESI solvent composition ws 47.5%/47.5% methnol/wter with 5% cetic cid. Anlyticl stndrd delivery ws performed vi six-port (Vlco Industries, Houston, TX) injection port nd n externl (70 µl) injection loop. The IMS drift tube consisted of two regions: (1) desolvtion region (13 cm in length), which served to completely remove excess solvent molecules from the ions prior to entry into the drift region, nd the drift region (22.5 cm in length). A positive voltge (ll experiments were performed in the positive mode) of 10 kv ws pplied to the electronic ion gte, which equted to n verge drift field of 385 V/cm. Nitrogen ws employed s the drift gs nd ESI cooling gs (flow rtes of 800 nd 100 ml/min, respectively). Both IMS regions were mintined t temperture of 250 C. The IMS ws interfced to 150-QC ABB-Extrel (Pittsburgh, PA) qudrupole mss spectrometer vi 40-µm pinhole interfce. A series of six Einzel lenses were plced fter the drift tube nd were operted t the following voltges (listed in order): +8.0 (pinhole), (screen), (first element of einzel), (second element of einzel), (third element of einzel), nd V (ELFS plte). The dynode nd electron multiplier were operted t -5.0 nd 1.7 kv, respectively, nd the qudrupole mss filter ws bised t V. The current signl ws collected with Keithley model 427 mplifier (Keithley Instruments, Clevelnd, OH) nd mplified (10 9 gin), nd the signl ws sent to Lbview (Ntionl Instruments, Houston, TX) dt cquisition system. All spectr were the result of 1000 verges obtined with gte pulse width of 0.2 ms nd totl scn time of 50.0 ms. Due to overhed from Lbview dt processing, ech spectrum took 70 s to obtin. All IMS spectr presented were obtined in one of two instrumentl opertion modes: non-mss-selective nd mss-selective ion monitoring (SIM). For the first mode (rf only), the qudrupole served to trnsmit ions from the IMS drift tube to the electron multiplier. For SIM, the qudrupole selectively trnsmitted one m/z vlue from the IMS tube. Clcultions. All reduced mobility constnts (K o ) nd collision cross-section () vlues were clculted from experimentlly determined drift times (t d ). The reduced mobility constnts were clculted ccording to the following eqution: K o ) ( L2 Vt d)( 273 T )( 760) P (1) where L ws the drift region length (22.5 cm), V ws the drift voltge (8680 V), T ws the effective temperture in the drift region (523 K), nd P ws the pressure in the drift region ( Torr). The verge ion collision cross section () ws clculted from the following eqution: 26 ) ( 16N)( 3 µkt) 1/2( 2π zevt d L ) (2) 2 where z is the number of the chrges on the ion, e is the chrge of one proton, N is the number density of the drift gs, µ [) mm/ (m + M)] is the reduced mss of n ion (m) nd the neutrl drift gs (M), nd k is Boltzmnn s constnt. RESULTS AND DISCUSSION In Figure 1, the structures for the seven opite compounds studied re shown. The moleculr weight for ech compound is lso presented nd listed in the order of incresing mss. Three bused drugs (heroin, codeine, nd morphine) nd four primry metbolites were evluted. The differences in the structures were due to functionl group plcement t one or more of the three sites, R 1,R 2,orR 3. Norcodeine nd normorphine re the demethylted derivtives of codeine nd morphine, respectively. MAC nd MAM re the cetylted derivtives for codeine nd morphine, respectively. For ll seven compounds, both nonselective IMS spectr nd SIM spectr were obtined to mss identify ech ion mobility pek tht ws observed. The reduced mobility constnts (K o ) nd corresponding m/z vlues for the seven compounds re listed in Tble 1. Severl trends in ion formtion cn be elucidted from Tble 1. First, ll seven compounds formed protonted moleculr (21) Trszk, J. A.; Li, J.; Clemmer, D. E. J. Phys. Chem. B 2000, 104, (22) Countermn, A. E.; Vlentine, S. J.; Sreblus, C. A.; Henderson, S. C.; Hoglund, C. S.; Clemmer, D. E. J. Am. Soc. Mss Spectrom. 1998, 9, (23) Vlentine, S. J.; Anderson, J. G.; Ellington, A. D.; Clemmer, D. E. J. Phys. Chem. B 1997, 101, (24) Wu, C.; Klsmeier, J.; Hill, H. H., Jr. Rpid Comm. Mss Spectrom. 1999, 13, (25) Wyttenbch, T.; von Helden, G.; Bowers, M. T. J. Am. Chem. Soc. 1996, 118, (26) Revercomb, H. E.; Mson, E. A. Anl. Chem. 1975, 47, Anlyticl Chemistry, Vol. 73, No. 8, April 15,

3 Tble 1. Reduced Mobility Vlues nd Mss Identities for Ions Formed from Seven Opite Compounds compound ion M - 18 M + 1 M + 23 M - 59 (M - H 2O) + (MH) + (M + N) + (M - COOCH 3) + normorphine K o (cm 2 V -1 s -1 ) m/z morphine K o (cm 2 V -1 s -1 ) m/z norcodeine K o (cm 2 V -1 s -1 ) m/z codeine K o (cm 2 V -1 s -1 ) m/z monocetyl morphine K o (cm 2 V -1 s -1 ) m/z monocetyl codeine K o (cm 2 V -1 s -1 ) m/z heroin K o (cm 2 V -1 s -1 ) m/z Identified s M - 43 ion for heroin. Figure 1. Structure of seven opite compounds evluted in this study. ion nd six of seven formed sodium dduct (except norcodeine). The noncetylted opites (normorphine, morphine, codeine, nd norcodeine) lso formed n (M - 18) + ion which is thought to be the loss of wter (M - H 2 O) +. Similrly, ions contining cetyl groups, MAM, MAC, nd heroin, formed (M - 59) + ions which corresponds to the loss of n cetyl group (COOCH 3 ). In ddition, the ESI of heroin formed fourth ion, (M - 43) +, the loss of COCH 3 group. The moleculr decompositions re similr to results from previous IMS studies tht utilized rdioctive sources for ioniztion of opites 27 nd for other drug molecules contining hydroxyl groups. 28 In contrst, studies using ESI-MS hve shown tht only the protonted ions were observed in the mss spectrum. 2,3 (27) Lwrence, A. H. Anl. Chem. 1988, 58, (28) Lwrence, A. H. Anl. Chem. 1989, 59, Figure 2. Nonselective ESI-IMS/MS spectr of four noncetylted compounds: () normorphine, (b) morphine, (c) norcodeine, nd (d) codeine. Products ion for ech compound were mss identified to be (1) (M - H 2O) +, (2) MH +, nd (3) (M + N) +. Although similr frgmenttion hs been seen by incresed skimmer voltges in ESI-MS, the unique mobilities for the decomposition products indicted tht the frgmenttion occurred prior to beginning the ion mobility experiment. The difference in the ioniztion process is not obvious, lthough fundmentl understnding of the difference would enble mnipultion of experimentl prmeters to gin moleculr informtion. Bsed on these structurl observtions nd distinguishing functionl group losses, the following results re broken into two groupings: noncetylted opites nd cetylted opites Anlyticl Chemistry, Vol. 73, No. 8, April 15, 2001

4 Tble 2. Mesured Collision Cross Sections of Four Noncetylted Opite Compounds nd Reltive Increse with Additionl Functionl Groups nd Ionic Size ion NM M NC (M - H 2O) Å Å Å Å 2 V% MH Å Å Å Å 2 V% (M + N) Å Å Å 2 Reltive increse in collision cross section from previous row/ column to next. C Tble 3. Mesured Collision Cross Sections of Monocetylted nd Bicetylted Opite Compounds nd Reltive Increse with Additionl Functionl Groups nd Ionic Size ion MAM MAC HER (M - COOCH 3) Å Å Å 2 V% MH Å Å Å 2 V% (M + N) Å Å Å 2 V% (M - COCH 3) 144 Reltive increse in collision cross section from previous row/ column to next. Figure 3. SIM ESI-IMS/MS spectr showing seprtion of two isomers: (1) morphine nd (2) norcodeine; m/z 267 (M - H 2O) +, 286 MH +, nd z 308 (M + N) +. IMS Spectr for Noncetylted Opites. Nonselective ESI- IMS/MS spectr for the four noncetylted opites re shown in Figure 2. Although not presented in Figure 2, ech observed mobility pek ws lso mss identified to determine the ion identity nd ech is lbeled s (1) (M - H 2 O) +, (2) MH +, nd (3) (M + N) + for the four compounds: () normorphine, (b) morphine, (c) norcodeine, nd (d) codeine. Although the ion formtion for the four opites is similr, there re differences in the reltive responses tht llude to structurl dependences on ion formtion in ESI. First, the overll signl intensities for normorphine nd morphine MH + ions were 60% less thn those observed for codeine nd norcodeine. The structurl difference in the two groups is methyl group on the R 1 oxygen group (refer to Figure 1). Signl intensity rtios (M - 18:M + 1, M + 1:M + 23) were found to be greter for codeine nd norcodeine, s well. The ddition of the methyl group on the R 1 group seems to hve n ffect on ESI ion signl intensity. The formtion of ll three ions (loss of wter, protonted ion, nd sodium dduct) ws incresed by the methyl ddition nd cn be observed by specultion in Figure 2 ( nd b compred to c nd d). As seen in Figure 2, incresing ion msses correlted with longer drift times nd, hence, lower K o vlues. Although this Figure 4. () Nonselective nd (b) SIM ESI-IMS/MS spectr of 6-monocetyl codeine; m/z 282 (M - COOCH 3) +, 342 MH +, nd 364 (M + N) +. generl reltionship ws expected nd observed, the reltive increse for ech compound ws dependent on the moleculr structure. Both the collision cross sections nd percent increse in cross section re listed in Tble 2 for the four compounds. For normorphine, ddition of sodium to the molecule incresed the collision cross section by 1.4%. In comprison, both morphine nd codeine collision cross sections incresed (ddition of sodium) by 2.7%. This difference in collision cross section due to the sodium ddition indicte tht there could be differences in the plcement of sodium on the molecule. Although morphine (Figure 2b) nd norcodeine (Figure 2c) were isomers, differing in the plcement of methyl group (R 3 on morphine, R 1 on norcodeine), inspection of the IMS spectr for the two compounds shows tht the drift times were different for the two ions. This difference ws further elucidted by prepring the two isomers in mixture nd evluting their seprtion. Figure 3 shows the SIM spectr for ech ion formed Anlyticl Chemistry, Vol. 73, No. 8, April 15,

5 Figure 5. () Nonselective nd (b) SIM ESI-IMS/MS spectr of 6-monocetyl morphine; m/z 266 (M-COOCH 3) +, m/z 328 MH +, nd m/z 350 (M+N) +. Figure 6. () Nonselective nd (b) SIM ESI-IMS/MS spectr of heroin; m/z 310 (M - COOCH 3) +, 327 (M - COCH 3) +, 370 MH +, nd 392 (M + N) +. for the two isomeric compounds: (1) morphine nd (2) norcodeine. It cn be seen tht, for both the (M - H 2 O) + nd MH + ions, the morphine ions drifted fster thn the norcodeine ions. Bseline seprtion ws esily obtinble for the two isomers, demonstrting significnt dvntge of IMS seprtion. IMS Spectr for Acetylted Opites. In Tble 3, the collision cross sections for the three cetylted molecules re shown. As expected, the ions tht lost COOCH 3 (59) group hd lower collision cross section thn the MH + ion which differed by pproximtely 12-15%. Acetyltion of either oxygen tom (R 1 for MAM nd MAC, R 1 nd R 2 for heroin) ltered the reltive mobilities for the MH + ion nd sodium dduct. In Figure 4, both the nonselective () nd SIM (b) IMS/MS spectr for MAC re shown. In the top nonselective IMS spectr, only two peks re observed. Upon mss identifying ech pek (b), it ws determined tht the pek t 25 ms correlted to the M - 59 ion nd the lrger pek t 28 ms is due to both the protonted moleculr ion (28.2 ms) nd sodium dduct (28.4 ms). The two ion collision cross sections (161 nd 162 Å 2, respectively) differ by 0.6% compred to 2.7% for the noncetylted counterprt, codeine. The ffect of the sodium on ion conformtion hd n even greter impct on the ion mobility spectrum of MAM nd heroin. In Figure 5, similr ion mobility representtion is shown for MAM (, nonselective mode; b, SIM mode). While the decetylted ion drifts for 24 ms, both the protonted nd sodited ions hve drift times of 27 ms. The interction with the sodium tom ppers to be even stronger for the MAM molecule, nd the two ions (protonted nd sodited ions) re pproximtely the sme size. Figure 7. Grph showing reltionship between m/z nd K o vlues for opite ions: (f) MH +,(O) (M+ N) +,(9) (M- H 2O) +, nd (b) (M - COOCH 3). The replcement of the methyl group on MAC with COCH 3 results in the formtion of heroin. In Figure 6, both the nonselective nd SIM IMS spectr re shown. Comprison of the lower two SIM spectr (m/z 370 (MH + ) nd 392 (M + N) + ) shows tht the sodium dduct drifted fster in the ion mobility tube thn the protonted ion. This implies tht the sodited ion ctully formed smller structure (lower collision cross section) thn the moleculr ion. Upon inspection of the structures (see Figure 1) nd the mobility results, it suggests tht the electronegtive oxygen groups due to cetyltion my interct with the sodium to form compcted ion. Seprtion of Opites by ESI-IMS/MS. Although IMS mobilities nd m/z vlues re not completely independent, the higher resolution of our instrument enbles smll differences in mobilities to be mesured. In Figure 7, the mesured K o vlues 1668 Anlyticl Chemistry, Vol. 73, No. 8, April 15, 2001

6 Although, some mobility peks overlp in the nonselective IMS spectr, ech SIM spectr (for the protonted moleculr ions) re shown in Figure 8b nd cn be identified by ech ion s unique K o :m/z reltionship. The complementry seprtion cpbilities of IMS nd MS enble opites s well s other smll drug molecules to be efficiently seprted. Figure 8. () Nonselective ESI-IMS/MS spectr of morphine mixtures contining normorphine, morphine, nd cetyl morphine. (1) (M - H 2O) + normorphine, (2) MH + normorphine, (3) (M - H 2O) + morphine, (4) (M - COOCH 3) + cetyl morphine, (5) MH + morphine, (6) (M + N) + normorphine, (7) (M + N) + morphine, (8) MH + cetyl morphine, nd (9) (M + N) + cetyl morphine. (b) SIM ESI-IMS/MS spectr of the three compounds; SIM spectr for ech compound re SIM spectr of protonted moleculr ion. for the opite ions were grphed with ech ion s corresponding m/z vlue. For ll but two sets of ions, ech ion hd unique m/z nd/or K o vlue. Therefore, the two-dimensionl seprtion cpbility of IMS/MS ws relized. Figure 8 shows n ESI-IMS/MS seprtion of morphine nd its two primry metbolites, normorphine nd cetyl morphine. CONCLUSIONS The results of this study show two beneficil fetures of ESI- IMS/MS s tool for opite seprtion. First, with our highresolution instrument, the two-dimensionl seprtion of the three opites nd metbolites ws relized. Becuse IMS seprtes ions on the bsis of size/chrge density, it ws found tht the predominnt ions hd unique K o :m/z vlue. Not only ws the seprtion possible, but the seprtion ws performed in 70 s. This is significnt enhncement in nlysis times nd could produce higher smple throughput. Metbolic isomers were found to be esily seprted nd hd substntilly different mobilities. In mny phrmcokinetic studies, the cpbility of identifying isomers is importnt nd this work shows tht the unique seprtion of IMS could contribute to these type of studies. The findings of this study lso lluded to more fundmentl contributions of IMS. The difference in moleculr ion nd sodited ion mobilities provided insights into the underlying conformtions of the ions nd, subsequently, the molecules themselves. Heroin ws found to form more compct structure when ssocited with sodium ion thn the protonted ion. This study provides n exmple of the size nd conformtion informtion tht cn be determined by determining ion mobilities. Received for review September 26, Accepted Jnury 11, AC001147B Anlyticl Chemistry, Vol. 73, No. 8, April 15,