Accurate mass measurement at enhanced mass-resolution on a triple quadrupole mass-spectrometer for the identification of a reaction impurity and collisionally-induced fragment ions

RAPID COMMUNICATIONS IN MASS SPECTROMETRY

Rapid Commun. Mass Spectrom. 2003; 17: 561–568

Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/rcm.952

Accurate mass measurement at enhanced mass-resolution

on a triple quadrupole mass-spectrometer for the

identification of a reaction impurity and

collisionally-induced fragment ions of cabergoline

Gary Paul1*, Witold Winnik1, Nicola Hughes2, Hans Schweingruber3, Rexford Heller3

and Alan Schoen3

1Thermo Finnigan, 265 Davidson Avenue, Suite 101, Somerset, NJ 08873, USA2Biovail Contract Research, 460 Comstock Road, Toronto, Ontario, M1L 4S4, Canada3Thermo Finnigan, 355 River Oaks Parkway, San Jose, CA 95134, USA

Received 8 January 2003; Revised 15 January 2003; Accepted 16 January 2003

In this study, accurate mass measurements were made by electrospray ionization (ESI) on a triple

quadrupole mass spectrometer operating in enhanced mass-resolution mode (peak width¼ 0.1

u FWMH), to give qualitative information relating to the pharmaceutical, cabergoline. Accurate

mass determinations by ESI-MS were performed on a protonated impurity formed during cabergo-

line storage. The accurate mass measurement resulted in only one proposed elemental composition

for the impurity, using reasonable elemental limits and mass tolerance for the calculation. This

information was sufficient to propose a structure for the impurity where ESI-MS/MS proved con-

sistent. The difference between the accurate mass measurement and the exact mass calculated for

the proposed structure was 0.8mmu, with a standard deviation of 0.7mmu for replicate accurate

mass determinations. Accurate mass determinations in ESI-MS/MS provided information on caber-

goline fragment ions formed through collisionally-induced dissociation. Since the potential forma-

tion of isobaric ions exists for two major cabergoline fragment ions, accurate mass measurement

allowed for the determination of the most probable fragment ion structures. The differences

between the accurate mass measurements and exact masses calculated for the proposed fragment

ions were 1.9 and 2.1mmu, with standard deviations of 0.4 and 0.8mmu, respectively, for replicate

determinations. Copyright # 2003 John Wiley & Sons, Ltd.

Cabergoline (Scheme 1) is a synthetic ergoline derivative with

powerful dopaminergic activity that achieves the desired

therapeutic effect when administered at low doses. Conse-

quently, systemic plasma levels of cabergoline are extremely

low (pg/mL level), and very sensitive techniques are

required for detection.1,2 In a recent quantitative study on

cabergoline by LC/ESI-SRM using a triple quadrupole

mass spectrometer with enhanced mass-resolution capabil-

ities, a detection limit of 50 fg on-column was achieved which

is suitable for pharmacokinetic analysis of this important

pharmaceutical.3 In addition, an extended linear dynamic

range spanning five orders of magnitude was covered with

precision and accuracy values well within pharmaceutical

industry standards.3 A quantitative LC/APCI-SRM study

involving a related synthetic ergoline derivative, pergolide,

found that use of the enhanced mass-resolution feature of

the triple quadrupole mass spectrometer gave further

improvement in sensitivity relative to unit mass-resolution

operation, as well as a broader linear dynamic range.3

Improved API-SRM sensitivities at enhanced mass-resolu-

tion relative to unit mass-resolution have also been reported

in quantitative studies involving other analytes.4,5

In addition to the high-performance quantitation capabil-

ities,3,6 the enhanced mass-resolution feature also broadens

the qualitative abilities of a triple quadrupole mass spectro-

meter. Enhanced mass-resolution has been employed to

separate isobaric interference ions as close as 0.1 u from the

analyte of interest on a triple quadrupole mass spectrometer,

where interference-free MS/MS of the analyte can be

obtained for identification purposes.6,7 Charge states for

peptide ions up to 13þ (for ubiquitin) have also been readily

determined using the enhanced mass-resolution capability.

One of the most significant advances involving the

enhanced mass-resolution triple quadrupole mass spectro-

meter is in the field of accurate mass measurement.

Preliminary accurate mass determinations have been

recently reported, both for protonated molecules in ESI-MS

and fragment ions in ESI-MS/MS, on the triple quadrupole

mass spectrometer used in this study, operating in enhanced

mass-resolution mode.8 The experimentally-determined

accurate mass measurements for known standards and

Copyright # 2003 John Wiley & Sons, Ltd.

*Correspondence to: G. Paul, Thermo Finnigan, 265 DavidsonAvenue, Suite 101, Somerset, NJ 08873, USA.E-mail: [email protected]

fragments were typically within 2 mmu of theoretical exact

masses.8 Thus, this instrument has the potential to be highly

beneficial in the structural elucidation of unknowns such as

metabolites, tryptic peptides and impurities. Mass measure-

ments of comparable accuracy for protonated molecules have

also been reported on unit mass-resolution quadrupole

instruments in positive and negative ESI-MS, validating the

legitimacy of quadrupole mass analyzers to perform these

experiments.9,10 However, a major issue in the use of unit

mass-resolution quadrupoles for accurate mass measure-

ment is the commonplace problem of having unresolved

interferences present in the analyte ion peak. These unre-

solved interferences have a negative effect on the accuracy of

the mass measurement, even at only small relative ion

intensities.9,10 With the enhanced mass-resolution capability

of the triple quadrupole mass spectrometer used in this

study, the likelihood of overlap from interfering ions is

greatly reduced, thus making the accurate mass-measuring

technique more rugged.

In the work presented herein, accurate mass measurement

in ESI-MS on a triple quadrupole mass spectrometer operated

at enhanced mass-resolution was used to identify a reaction

impurity formed upon prolonged storage of cabergoline in

methanol at room temperature. In addition, accurate mass

measurement in ESI-MS/MS of two major cabergoline

fragment ions formed by collision-induced dissociation

(CID) helped elucidate the fragmentation pathway of

cabergoline involving these fragment ions and provided

structural information. Hence, the qualitative information

obtained on cabergoline through accurate mass measure-

ment augments the quantitative data previously obtained on

the enhanced mass-resolution triple quadrupole mass spec-

trometer.3

EXPERIMENTAL

Chemically synthesized cabergoline (purity >99%) was pre-

pared at a concentration of �100 ng/mL in HPLC-grade

methanol (EM Sciences, Gibbstown, NJ, USA) and stored at

�258C. HPLC analysis was performed using a LC Surveyor

system (Thermo Finnigan, San Jose, CA, USA). Chromato-

graphic separation for the accurate mass determinations

was achieved using isocratic conditions on a 50� 2 mm,

3 mm, HyPURITY Hypersil column (Thermo Hypersil-Key-

stone, Bellefonte, PA, USA) with a mobile phase of metha-

nol/water/acetic acid (75:25:1). The LC flow rate was

300mL/min and the injection volume was 10 mL.

All accurate mass determinations were performed in ESI

mode using a TSQ Quantum AM triple quadrupole mass

spectrometer (Thermo Finnigan), utilizing the enhanced

mass-resolution capability of this instrument. The TSQ

Quantum AM instrument contains a thermally stabilized

analyzer control board with a virtual digital-to-analog (DAC)

converter subsystem designed specifically for accurate mass

measurement. Accurate mass measurement is achieved on

the TSQ Quantum AM by the following calibration proce-

dure. First, the DACs are corrected for their non-linearity

through internal calibration. The next two calibration steps

then provide a mass scan function that is truly linear with

mass. With this accomplished, the positions of known lock-

mass peaks are measured precisely and a final lock-mass

algorithm applies a simple linear correction to interpolate

precisely between the lock peaks and accurately assign

measured masses for ions of interest. A more detailed

discussion of accurate mass measurement on the TSQ

Quantum AM will be the subject of a future publication

(Schoen A, Heller R, Schweingruber H, Winnik W, Bui H,

Maljers L, Mulholland J, Olney TN, Campbell C, Churchill M,

Paul G, in preparation).

Accurate mass measurement of [MþH]þ ions for a reaction

impurity, formed upon prolonged storage of cabergoline in

methanol at room temperature, was achieved by LC/ESI-MS.

The ESI parameters were as follows: spray voltage, 5.0 kV;

sheath gas (nitrogen, purity>99.99%; Airgas East Inc., Salem,

NH, USA) flow, 70 arbitrary units; auxiliary gas (nitrogen)

flow, 10 arbitrary units; ion transfer tube temperature, 3608C.

An internal mass-locking procedure was employed for

accurate mass measurement; the reference, polyethylene

glycol (PEG), and the impurity were both present in the ESI

source at the same time. An equimolar mixture of PEG 200,

300 and 400 (concentration�50 pM/mL) in methanol/water/

ammonium acetate (50:50:20 mM) was mixed via a T-junction

into the LC flow post-column at a flow rate of 2mL/min, and

12 replicate LC injections of the reaction impurity were made.

ESI-MS data for the impurity [MþH]þ and appropriate PEG

cluster ions for mass-locking were collected through single

ion monitoring (SIM) in the centroid mode, after first

checking for symmetrical peak shapes in the profile mode.

Scan widths of 0.6 u and a scan rate of 10 u/s were used in

SIM. Mass-correction of the reference peaks for each scan

Scheme 1. Proposed reaction scheme for the formation of the impurity ion at m/z 311 in ESI-MS.

Copyright # 2003 John Wiley & Sons, Ltd. Rapid Commun. Mass Spectrom. 2003; 17: 561–568

562 G. Paul et al.

takes place in real time so that the masses reported for

[MþH]þ are already corrected. The final accurate mass

determination of the impurity [MþH]þ ions for each LC peak

was an average of accurate mass measurements from at least

ten individual scans. Prior to LC injections of the reaction

impurity, accurate mass determinations of known PEG

cluster ions, whose masses were not used as lock-masses,

were taken in order to check the accuracy of the mass-

measuring technique. The experimentally-determined accu-

rate mass measurements for these cluster ions were consis-

tently within 1 mmu of their known exact mass values, using

surrounding PEG cluster ions for mass-locking. The quadru-

pole mass analyzer, Q1, was set at an enhanced mass-

resolution of 0.1 u FWHM throughout, in order to reduce the

likelihood of erroneous accurate mass determinations

through unresolved interferences.

Accurate mass measurement of cabergoline fragment ions

was achieved by ESI-MS/MS. The ESI parameters were as

described above and the MS/MS conditions were: argon

collision gas pressure, 1.3 mTorr; collision energy, 29 eV. An

external procedure was employed for the mass-locking of the

appropriate PEG calibrant ions, followed by accurate mass

measurement of the fragment ions of interest upon on-

column injections of cabergoline. The ESI-MS/MS conditions

described above were also used for the external mass-locking

procedure, so as to ensure the best possible accuracy for the

subsequent accurate mass determinations. For calibration, an

equimolar mixture of PEG 200, 300 and 400 (concentration

�50 pM/mL, flow rate 2mL/min) was mixed via a T-junction

into the LC flow post-column. ESI-MS/MS data for the PEG

cluster ions of interest were collected in neutral-loss scanning

mode in which a mass loss of 0 u was monitored. Q1 was

operated at an open mass-resolution setting of 3 u FWHM,

while Q3 was held at the enhanced mass-resolution setting of

0.1 u FWHM. Fifty scans of the PEG cluster ions were

collected and averaged in the centroid mode. The cluster

ion masses were then locked to their exact mass values, and

the delta-mass values were frozen. With the external mass-

locking calibration procedure complete, the flow of the PEG

mixture into the ESI source was stopped. Four replicate LC

injections of cabergoline were then made, with Q1 now

parked at the m/z value for the prercursor ion ([MþH]þ for

cabergoline, m/z 452.3) with a unit-mass resolution setting

(0.7 u FWHM). Q3 remained at the enhanced mass-resolution

setting of 0.1 u FWHM. The ESI-MS/MS data for the fragment

ions was collected in product ion scanning mode. All scans

recorded had the m/z values corrected in real time utilizing

the frozen delta-mass values, so that corrected masses for the

fragment ions were reported directly. The accurate mass

determinations of the fragment ions from each LC peak were

averages of accurate mass measurements from at least eight

individual scans. ESI-MS/MS data for the PEG lock-mass

ions and cabergoline fragment ions were collected by SIM in

the centroid mode, using a scan width of 0.6 u and a scan rate

of 10 u/s.

RESULTS AND DISCUSSION

The accurate mass measurement capability of the enhanced

mass-resolution triple quadrupole mass spectrometer was

first employed in the analysis of an impurity identified in

stock solutions of cabergoline prepared in methanol. The

infusion ESI mass spectrum for a solution of cabergoline

that had been stored in methanol at room temperature for a

prolonged length of time is shown in Fig. 1. The spectrum

is dominated by a peak at m/z 311, and no significant signal

corresponding to protonated cabergoline at m/z 452 is

observed. LC/ESI-MS analysis of the same solution revealed

two separate LC peaks for components with [MþH]þ of m/z

311 and 452; the intensity of the m/z 311 LC peak was much

greater than that of the m/z 452 component. The observation

of two separate LC peaks confirms that the ion at m/z 311 is

not a product of in-source ESI processes involving cabergo-

line. The formation of an impurity of MW 310 through the

decomposition of cabergoline in methanol over time is con-

sistent with the ESI-MS data.

Figure 1. Infusion ESI mass spectrum for cabergoline after prolonged storage in methanol

at room temperature.

Accurate mass measurement on an enhanced TSQ 563


In order to identify this impurity, accurate mass measure-

ment of the protonated molecule atm/z 311 was performed by

LC/ESI-MS on the triple quadrupole mass spectrometer

operating in enhanced mass-resolution mode (Q1, 0.1 u

FWHM). An internal mass-locking procedure, continually

calibrating the mass scale from scan to scan, was performed

using the [PEGnþNH4]þ cluster ions at m/z 300.2022 (n¼ 6)

and 344.2284 (n¼ 7) to bracket the m/z 311 ion of interest. The

accurate mass determinations of [MþH]þ for the 12 LC

injections of the impurity-containing solution are shown in

Table 1. An average accurate mass determination of m/z

311.1752 was obtained for the impurity [MþH]þ with a

standard deviation of 0.7 mmu (Table 1).

This experimentally determined accurate mass measure-

ment of [MþH]þ, m/z 311.1752, was submitted to an

elemental composition calculator (Xcalibur 1.3 software,

Thermo Finnigan), in order to determine the elemental

composition of the impurity. The maximum elemental limits

for this calculation were set through addition of the elemental

compositions of the potential reactants, cabergoline and

methanol, and the minimum was held at zero; thus the limits

were C[0-27], H[0-41], N[0-4], O[0-3]. A maximum of four

nitrogen atoms was used instead of five, since an even

molecular weight for the impurity (MW 310) means that there

must be an even number of nitrogens present in the molecule

(‘nitrogen rule’). By setting a tolerance of �5 mmu on the

accurate mass measurement, only one elemental composition

was returned for the protonated impurity, namely,

C19H23N2O2. The difference between the experimentally-

determined accurate mass measurement and the exact mass

calculated for this elemental composition is 0.8 mmu. This

level of accuracy for [MþH]þ is consistent with previous

accurate mass determinations for protonated molecules of

known mass by ESI-MS on the enhanced mass-resolution

triple quadrupole mass spectrometer.8 The reported stan-

dard deviations of those accurate mass measurements were

also of a similar magnitude to that shown here.8 Using the

determined elemental composition, a rational reaction

scheme and structure for the impurity were proposed, shown

in Scheme 1.

In order to provide confirmation of the proposed structure

(Scheme 1), ESI-MS/MS of the impurity [MþH]þ ion was

performed. The ESI-MS/MS mass spectrum is shown in

Fig. 2. The formation of four significant fragment ions at m/z

269, 237, 209 and 168 from the proposed impurity structure

can be readily rationalized, as shown in Scheme 2. These ESI-

MS/MS fragmentation processes were also verified by Mass

FrontierTM 3.0 (Thermo Finnigan), a software package which

predicts feasible CID fragmentation pathways for analyte

ions of interest.11

An in vivo study of the metabolism of cabergoline in

humans12 also provides interesting information related to the

impurity identified in this work (structure I). The major

metabolite of cabergoline found in urine is the corresponding

acid derivative of cabergoline (structure II) where hydrolysis,

rather than oxidation, was the primary metabolic pathway.12

Table 1. Accurate mass determinations for the impurity

[MþH]þ ion at m/z 311 by ESI-MS. Measurements for 12

replicate LC injections

Determined accurate mass for[MþH]þ at m/z 311 (u)

Injection 1 311.1749Injection 2 311.1736Injection 3 311.1757Injection 4 311.1755Injection 5 311.1756Injection 6 311.1747Injection 7 311.1752Injection 8 311.1760Injection 9 311.1754Injection 10 311.1753Injection 11 311.1742Injection 12 311.1760Average 311.1752Standard Deviation 0.7 mmu

Figure 2. LC/ESI-MS/MS spectrum of impurity [MþH]þ at m/z 311; collision energy: 20 eV,

collision gas pressure: 1.5mTorr.

564 G. Paul et al.


Hence, the formation of the impurity after prolonged storage

of cabergoline in methanol at room temperature is analogous

to the hydrolysis metabolic pathway observed in vivo.

The accurate mass determination for the protonated mole-

cule collected on the triple quadrupole mass spectrometer

proved essential in solving the identity of the reaction

impurity. Obviously, the formation of impurities from

decomposition of an analyte in solution is deleterious to

quantitation studies, so this finding represents important

information in terms of cabergoline stability and storage. As a

consequence of the decomposition of cabergoline in metha-

nol at room temperature, it was decided to perform an

experiment under the same conditions, but where cabergo-

line was dissolved in a different solvent, acetonitrile. The

resultant ESI mass spectrum showed only one significant ion

at m/z 452, corresponding to protonated cabergoline. The

absence of the impurity ion at m/z 311 in acetonitrile is

consistent with this impurity being formed upon reaction of

cabergoline with methanol.

The ESI-MS/MS behavior of cabergoline was also inves-

tigated utilizing the accurate mass measurement capabilities

of the triple quadrupole mass spectrometer. The ESI-MS/MS

spectrum for the precursor ion [MþH]þ of cabergoline is

shown in Fig. 3. The m/z 381 fragment ion is most intense,

which was expected since the SRM transition involving this

fragmentation process was used for high sensitivity quanti-

tation of cabergoline in previous studies.3,13 Rationalization

of the ESI-MS/MS fragmentation pathways for cabergoline

was sought using the Mass FrontierTM 3.0 software. Various

CID pathways, accompanied by fragment ion structures,

were proposed by the software and these predictions were

compared with the actual ions present in the ESI-MS/MS

spectrum (Fig. 3). The potential fragmentation routes invol-

ving the most intense m/z 381 and 336 fragment ions seen in

ESI-MS/MS are shown in Scheme 3. Of the predicted

pathways, only one route contained both m/z 381 and 336

fragment ions (I and II, Scheme 3). However, alternate

pathways involving isobaric fragment ions at m/z 381 (III,

Scheme 3) andm/z 336 (V, Scheme 3), with different elemental

compositions, were also proposed by the software. In

contrast, all the software-predicted MS/MS fragmentation

processes leading to the formation of the significant cabergo-

line fragment ion at m/z 279 (Fig. 3) yielded a consistent

fragment ion structure. To gain further information on which

of the proposed MS/MS fragmentation pathways shown in

Scheme 3 is prevalent for the formation of m/z 381 and 336

fragment ions, accurate mass measurement of these ions by

LC/ESI-MS/MS was performed. Q3 was held at an enhanced

mass-resolution setting of 0.1 u FWHM in order to reduce the

likelihood of unresolved interferences affecting the mass

accuracy.

The ESI-MS/MS accurate mass determinations of the m/z

381 and 336 fragment ions from four LC injections are shown

in Table 2. Calibration of the mass scale prior to the LC

injections was achieved through the external mass locking of

[PEGnþNa]þ cluster ions at m/z 305.1576, 349.1838 and

393.2101 (n¼ 6–8), which bracket the fragment ions of

interest. The formation of sodiated PEG cluster ions in ESI-

MS is commonplace due to the presence of sodium as an

impurity in the reference mixture. Sodiated PEG cluster ions

are very useful calibrants in ESI-MS/MS since the cluster ions

are strongly bound and can survive intact upon passing

through the pressurized Q2 collision cell. Accurate mass

measurements of m/z 381.2673 and 336.2097 were obtained

for the cabergoline fragment ions, with standard deviations

Scheme 2. Proposed CID fragmentation pathways for the impurity [MþH]þ at m/z 311.



of 0.4 and 0.8 mmu, respectively (Table 2). There was no

noticeable drift in the accurate mass determinations over the

time duration of the LC injections (<10 min) using the

external mass-locking procedure (Table 2).

The experimentally-determined accurate mass measure-

ments for the m/z 381 and 336 fragment ions are also entered

in Table 3, along with the exact masses of the isobaric MS/MS

fragment ions for m/z 381 and 336 (I, II, III, V; Scheme 3)

proposed by the software. A mass difference of �2 mmu is

observed between the accurate mass measurements and

exact masses calculated for them/z 381 and 336 fragment ions

I and II, while the isobaric fragment ions III and V differ by

Table 2. Accurate mass determinations for the m/z 381

and 336 fragment ions of cabergoline by ESI-MS/MS.

Measurements for four replicate LC injections

Determined accuratemass for m/z 381

fragment (u)

Determined accuratemass for m/z 336

fragment (u)

Injection 1 381.2677 336.2101Injection 2 381.2667 336.2103Injection 3 381.2673 336.2085Injection 4 381.2673 336.2099Average 381.2673 336.2097Standard Deviation 0.4 mmu 0.8 mmu

Figure 3. LC/ESI-MS/MS spectrum of cabergoline [MþH]þ at m/z 452; collision energy:

20 eV, collision gas pressure: 1.5mTorr.

Scheme 3. Proposed ESI-MS/MS fragmentation pathways for cabergoline [MþH]þ

involving the m/z 381 and 336 fragment ions. Fragmentation pathways predicted by the

Mass FrontierTM 3.0 software.

566 G. Paul et al.


�38 mmu (Table 3). Thus, the accurate mass determinations

are in good agreement with the fragment ions I and II that are

proposed in the same MS/MS fragmentation pathway

(Scheme 3), while formation of the isobaric fragment ions

III and V can be easily discounted because of the large mass

discrepancies (Table 3). The level of accuracy observed for

fragment ions I and II in this work (�2 mmu, Table 3) is

consistent with that achieved for a number of known

fragment ion species using the same technique.8 In contrast,

the mass difference of �38 mmu between the accurate mass

measurements and exact masses for fragment ions III and V is

well beyond the demonstrated mass accuracy of triple

quadrupole mass spectrometers operated either in enhanced

or unit mass-resolution mode.8–10

Hence, accurate mass measurement of the most intense

MS/MS fragment ions of cabergoline at m/z 381 and 336

allowed for the determination of the most likely CID

fragmentation route involving these ions, based on software

predictions of potential ESI-MS/MS fragmentation routes for

cabergoline. Accompanying structures for these cabergoline

fragment ions were also proposed by the software (Fig. 3) and

these were consistent with MS/MS fragment ions proposed

in a previous study involving cabergoline.13 However, in the

absence of accurate mass determinations in that study,13 the

possibility of isobaric fragment ion formation at m/z 381 and

336 could not be eliminated.

Information on the elemental compositions of the m/z 381

and 336 cabergoline fragment ions observed in ESI-MS/MS

can also be gained through the experimentally-determined

accurate mass measurements only. The accurate mass

measurements of the fragment ions (Table 2) were submitted

to the elemental composition calculator; the minimum

elemental limits were set at zero and the maximum limits

corresponded to the elemental composition of the cabergo-

line [MþH]þ ion. Setting a mass tolerance of � 5 mmu and

taking into account the nitrogen rule for the predominant

formation of even-electron fragment ions in ESI-MS/MS,

elemental compositions corresponding only to fragment ions

I and II (Scheme 3) were generated by the calculator.

CONCLUSIONS

In this work, accurate mass measurements were performed

using a triple quadrupole mass spectrometer, operated in

enhanced mass-resolution mode, to provide qualitative

information related to cabergoline. Accurate mass determi-

nations of a protonated molecule and MS/MS fragment

ions proved invaluable in the identification of a reaction

impurity formed upon the decomposition of cabergoline in

methanol, and also for the proposal of a major CID fragmen-

tation pathway of cabergoline, along with consistent frag-

ment ion structures. A major issue in the use of unit mass-

resolution quadrupoles for accurate mass measurement is

the commonplace problem of unresolved interferences that

have a negative effect on the accuracy of the mass measure-

ment even at only small relative ion intensities.9,10 The

enhanced mass-resolution capability of the triple quadrupole

mass spectrometer used in this study greatly reduces the like-

lihood of overlap from interfering ions.

The ability of the enhanced mass-resolution triple quadru-

pole mass spectrometer to provide accurate mass measure-

ments of protonated molecules and fragment ions, to a level

able to assist in structural elucidation, will make this

technique very useful in areas such as metabolite identifica-

tion. Analogous to the examples shown in this work, the

identification of an unknown metabolite can be achieved

through the accurate mass measurement of the protonated

molecule by ESI-MS, whilst information on the site of

biotransformation can be potentially gained through the

accurate mass measurement of CID fragment ions of the

metabolite by ESI-MS/MS. In combination with the demon-

strated ability to perform highly sensitive quantitation at unit

and enhanced mass-resolution,3,6 the enhanced mass-resolu-

tion triple quadrupole mass spectrometer should provide a

versatile tool with which to attack a variety of pharmaceutical

applications.

AcknowledgementsThe authors would like to thank Gabrielle Smith for her assis-

tance with this manuscript.

REFERENCES

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3. Hughes N, Winnik W, Dunyach JJ, Amad M, Splendore M,Paul G. J. Mass Spectrom. 2003; submitted.

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Table 3. Accurate mass determination, exact mass and mass difference for the proposed m/z 381 and 336 fragment ions of

cabergoline formed in ESI-MS/MS. The proposed m/z 381 and 336 fragment ions are shown in Scheme 3

m/z 381 m/z 336

Fragment IC23H33N4O

Fragment IIIC22H29N4O2

Fragment IIC21H26N3O

Fragment VC20H22N3O2

Exact mass (u) 381.2654 381.2291 336.2076 336.1712Determined mass (u) 381.2673 381.2673 336.2097 336.2097Difference (mmu) 1.9 38.2 2.1 38.5



7. Amad M, Winnik W, Schweingruber H, Mylechreest I, PaulG. Proc. 49th ASMSConf. Mass Spectrometry and Allied Topics,Chicago, IL, 2001.

8. Schoen AE, Heller RT, Schweingruber H, Dewey W, Bui H,Maljers L, Dunyach JJ, Olney TN, Taylor DM, Campbell C,Paul G, Churchill M. Proc. 50th ASMS Conf. Mass Spectro-metry and Allied Topics, Orlando, FL, 2002.

9. Tyler AN, Clayton E, Green BN. Anal. Chem. 1996; 68: 3561.

10. Kostianinen R, Tuominen J, Luukkanen L, Taskinen J,Green BN. Rapid Commun. Mass Spectrom. 1997; 11: 283.

11. Kagan M, Phillips J, Liu C. Thermo Finnigan ApplicationReport No. 307, Thermo Finnigan, San Jose, CA, 2002.

12. Cocchiara G, Benedetti MS. Drug Metabol. Drug Interact.1992; 10: 199.

13. Allevi C, Dostert P. Rapid Commun. Mass Spectrom. 1998; 12:33.

568 G. Paul et al.


Documents

Accurate mass measurement at enhanced mass-resolution on a triple quadrupole mass-spectrometer for the identification of a reaction impurity and collisionally-induced fragment ions