FOCUS: THE ORBITRAP

Performance Evaluation of a High-fieldOrbitrap Mass Analyzer

Alexander Makarov, Eduard Denisov, and Oliver LangeThermo Fisher Scientific, Bremen, Germany

A new design of the OrbitrapTM mass analyzer is presented. Higher frequencies of ion oscillationsand hence higher resolving power over fixed acquisition time are achieved by decreasing the gapbetween the inner and outer Orbitrap electrodes, thus providing higher field strength for agiven voltage. Experimental results confirm maximum FWHM resolving power in excess of350,000 at m/z 524 and 600,000 at m/z 195, isotopic resolution of proteins above 40 kDa, and asingle-shot dynamic range of 25,000. It was also found that mass shifts in the new designdepend very little on space charge inside the analyzer. This performance was achieved usinghigher voltages and by careful balancing of construction tolerances and operation parameters,which appeared to vary in narrower ranges of tuning than for a standard Orbitrapanalyzer. (J Am Soc Mass Spectrom 2009, 20, 1391–1396) © 2009 Published by Elsevier Inc. onbehalf of American Society for Mass Spectrometry

All trapping mass analyzers are known to benefitfrom increasing strength of the trapping field,major benefits being higher dynamic range,

repetition rate, resolving power, tolerance to spacecharge, etc. These benefits have become the majordriver in the quest for higher and higher field magnetsin Fourier transform ion cyclotron resonance (FT ICR)mass spectrometry [1, 2]. Similar improvements couldbe naturally expected for another prominent member ofFourier transform mass spectrometry family; the Orbi-trapTM mass analyzer [3, 4]. The electrostatic nature oftrapping in this analyzer determines the difference instrategies. In FT ICR the field strength could be increasedonly by changing the magnet to a more powerful one,the latter becoming the most expensive part of themass spectrometer, while in an electrostatic trap itcould be increased not only by applying highervoltages but also by changing geometry of the trap.

This work investigates, both theoretically and exper-imentally, the performance of the Orbitrap mass ana-lyzer with an optimized field structure, including adesign intended to provide increased field strength at agiven voltage.

Theoretical

Typically, the Orbitrap mass analyzer consists of anouter barrel-like electrode of maximum radius R2 and acentral spindle-like electrode along the axis of radius R1,with the outer electrode maintained at virtual ground ofpreamplifier and the central electrode at a voltage, �Ur

Address reprint requests to Dr. A. Makarov, Thermo Fisher Scientific

(Bremen) GmbH, Hanna-Kunath-Str. 11, 28199 Bremen, Germany. E-mail:alexander.makarov@thermofisher.com

© 2009 Published by Elsevier Inc. on behalf of American Society for M1044-0305/09/$32.00doi:10.1016/j.jasms.2009.01.005

(Ur � 0 for positive ions) [3, 4]. Thus, the generalequation for the quadro-logarithmic potential distribu-tion between the electrodes, U(r,z) [3], can be re-writtenin the form:

U (r, z) �k

2�z2 �(r2 � R1

2)

2 ��k

2· Rm

2 · ln� r

R1�� Ur (1)

where r, z are cylindrical coordinates (z � 0 being theplane of the symmetry of the field), k is the fieldcurvature, and Rm is the characteristic radius that cor-responds to radius at which dU(r,z) ⁄dr|z�0 � 0, i.e., thefield stops attracting stationary ions towards the axis andstarts to repel them (typically, Rm � R2�2 during elec-trostatic trapping [3]). Boundary condition U(R2,0) � 0allows one to determine the field curvature k, which inits turn defines the frequency of axial oscillations:

� �� e

(m ⁄ z)· k, (2)

where e is the elementary charge (1.602 � 10�19 C). Thelatter can be re-written as:

� ��e

(m ⁄ z)·

2 · Ur

Rm2 ln�R2

R1��

1

2�R2

2 � R12

(3)

This equation shows that the frequency increases pro-portionally to the square root of applied voltage Ur andinversely proportionally to the scaling of the trap (i.e.,simultaneous increase of Rm, R1, R2). As the frequency

increases, so do other important parameters: the maxi-

Published online January 18, 2009ass Spectrometry. Received December 6, 2008

Revised January 12, 2009Accepted January 12, 2009

1392 MAKAROV ET AL. J Am Soc Mass Spectrom 2009, 20, 1391–1396

mum resolving power and dynamic range over a fixedduration of acquisition, acquisition speed at a fixedresolving power, tolerance to space charge.

Thus, this equation reveals the most straightforwardways of improving Orbitrap performance: to increasevoltage on the central electrode and scale the trapdown. Unfortunately, straightforward solutions are notalways the best. For example, increase of voltage pro-vides relatively low “return on investment” because ofsquare-root dependence, whereas associated problemssuch as power dissipation, probability of breakdown,and required dimensions of isolators increase linearlyor quadratically with voltage. Similarly, geometricalscaling-down of the trap requires also scaling-down ofabsolute manufacturing tolerances and the injection slotto keep relative field perturbations under control. Theformer requires revision of manufacturing processeswhile the latter demands drastic changes of the injectionoptics to avoid loss of sensitivity because of quadraticscaling-down of the slot cross-section.

Another way to increase axial frequency in (eq 3)could be the change of ratios between Rm, R1, and R2.This approach could also be combined with any of thepreviously described approaches. In a standard Orbi-trap analyzer, R1 � 6 mm and R2 � 15 mm, i.e.,ln(R2/R1) � 0.916, which makes the first term in thedenominator in ( eq 3) dominating. This ratio becomesln(R2/R1) � 0.51 for R1 � 9 mm and unchanged Rm andR2 in the new design. Presence of the negative secondterm only enhances this change which results in fre-quency increase by a factor of 1.4, almost proportionallyto the factor of 1.5 change in R1. Frequency also could beincreased by reducing the characteristic radius Rm.However it has already been reduced in a standardOrbitrap analyzer close to the recommended minimumR2�2.

Simulation software that has been developed in-house and standard analytical models have been em-ployed for ion-optical design and evaluation of Orbi-trap electrodes with unchanged outer electrodes and anew central electrode. A new maximum radius of thecentral electrode (9 mm) was chosen to be as close aspossible to ion trajectories but still far enough to mini-mize the influence of manufacturing imperfections (Fig-ure 1). In addition, voltage on the central electrodeduring detection has been increased from the standardsetting of 3.5 kV to 5 kV, which results in the totalfrequency increase by a factor of F � 1.7. Similarly tohigh-field Fourier transform ion cyclotron resonance(FT ICR) instruments, the new design has been namedhigh-field Orbitrap (HF Orbitrap).

Increase of the field by this approach also results incertain adverse effects. One of them is the reduction ofthe image current on the outer electrodes as the largercentral electrode absorbs a significantly higher propor-tion of the image current due to its closer proximity toion trajectories. This effect was partially compensated

by increasing the gap between the split outer electrodes

by a factor of three to reduce overall capacitance ofdetection circuitry and improve signal-to-noise ratio.

Another adverse effect of a thicker central electrodeappeared to be reduced pumping of the trapping vol-ume. This effect was counteracted by making largerpumping apertures on the ends of the outer electrodes.As this change took place on the periphery of thetrapping field, its effect on ion-optical parameters wascalculated to be negligible.

One more effect, increase of the required initial ionenergy, comes directly from the increase of the fieldstrength. For an ion to move circularly at radius Rduring detection, equilibrium tangential velocity v�

should be [3]

(m ⁄ z) · v�2

2e�

k

4· Rm

2 � R2� (4)

Following off-axis injection in the Orbitrap mass ana-lyzer [3] at radius Ri, ions are subjected to electrody-namic squeezing by increasing voltage on the centralelectrode. Due to conservation of angular momentumion acceleration voltage V could be linked to tangentialvelocity v� via injection radius Ri and final radius R:

R · v� � Ri� 2 · eV

(m ⁄ z)(5)

As a result, ions need to be accelerated before enteringthe trap by voltage.

V �k

4· Rm

2 � R2� ·�R

Ri�2

(6)

When comparing a high-field Orbitrap analyzer (indexHF) and a standard one (index ST) for increase offrequency (eqs 2, 3) by factor F at constant Rm andinjection radius Ri, the acceleration voltage must in-

12 m

m

18 m

m

Standard Orbitrap High- field Orbitrap

(a) (b)

Figure 1. Comparison of a standard Orbitrap geometry (a) withthat of a high-field Orbitrap analyzer (b). Shape of outer electrodesis identical for both cases, largest i.d. of outer electrodes being30 mm.

crease as

1393J Am Soc Mass Spectrom 2009, 20, 1391–1396 HIGH-FIELD ORBITRAP

VHF

VST

� F2 ·�RHF

RST�2

(7)

wherein RHF and RST are final equilibrium radii inhigh-field and standard Orbitrap analyzer, respectively.Typically, RHF � 10 . . . 10.5 mm, RST � 9.10 mm, whichfor F � 1.7 results in (VHF/VST) � 3 . . . 3.5. This increaseis so great that it has required the re-design of existingelectronics driving the C-trap [4]. It also means thatcenter-of-mass collision energy of ions with back-ground gas scales up almost as fast as the accelerationvoltage (actually, as F2). Consequences of this featureare discussed below in relation to Figure 5.

Experimental

Using an LTQ™ Orbitrap XL mass spectrometer [4] as atest-bed and modified electronics, a standard commer-cial Orbitrap mass analyzer has been compared with anew design, featuring a thicker central electrode and the

200 400 600 800 1000 10

10

2030

40

50607080

90100 195.088

R=172001

262.636 R=145301

524.265 R=105401

1R

1121.99R=7310R

elat

ive

Abu

ndan

ce

0

20000

40000

60000

80000

100000

120000

140000

160000

180000

200000

0001001

m/z, Th

Res

olvi

ng p

ower

(a)

(b)

Figure 2. (a) Resolving power as a function of manalyzer [4]; high-field Orbitrap analyzer; FT ICR15 Tesla superconducting magnet. Acquisition ptime, single zero-filling and Kaiser-Bessel apodi

range m/z 150–2000 acquired using HF Orbitrap.

same outer electrodes (Figure 1). To improve the ulti-mate vacuum, higher power bake-out heaters wereemployed to raise bake-out temperature from the stan-dard 110 °C to 180 °C. This allowed pressure to gobelow 10�10 mbar level following just 12-h bake-outafter venting. Overheating of the preamplifier linked tothe chamber was avoided by water-cooling of its box.

Experiments were aimed to determine analyzer char-acteristics such as maximum resolution, resolution perdetect time, dynamic range, and tolerance to spacecharge. Frequency shifts caused by space charge havebeen compared with experimental results from a stan-dard LTQ Orbitrap XL instrument (with 3.5 kV centralelectrode voltage), 12 Tesla LTQ FT hybrid mass spec-trometer with Ultra cell from University of Illinois [5],as well as from a 14.5 Tesla Linear trap/FTICR instru-ment with a cylindrical ICR cell from National HighMagnetic Field Laboratory (NHMFL) [6]. Due to differ-ences in transfer efficiency, excitation amplitude, detec-tion circuitry, and processing software, direct compar-

1400 1600 1800 2000m/z, Th

1521.972R=62501

8501

1721.960 R=59501

1921.948R=56504

High-field orbitrap spectrum0.76 s acquisition time 0.94 s total cycle time

00001

Std OrbitrapHF Orbitrap 5kV7T FT ICR15T FT ICR

different FTMS instruments: Standard Orbitraph 7 Tesla superconducting magnet; FT ICR witheters are the same in all cases (0.76 s detection). (b) An example of a spectrum with the mass

200

321.9=672

71

/z forwit

aramzation

1394 MAKAROV ET AL. J Am Soc Mass Spectrom 2009, 20, 1391–1396

ison of detected ion numbers in these instrumentsappeared not to be straightforward. As all of theseinstruments share the same linear trap (LT) front-end[7] with the same calibration routine, it was the targetvalue of the linear trap that was used as a basis forestimating ion load. Target value of the LT is closelyrelated to the actual number of ions stored in it.

Experiments have been carried out using the stan-dard LTQ calibration mixture with caffeine, the peptideMRFA, and Ultramark 1600 dissolved in 25:25:49:1vol.vol.vol water/methanol/acetonitrile/acetic acid so-lution. Yeast enolase protein was obtained from Sigma-Aldrich Chemie GmbH (Munich, Germany) and usedwithout further purification.

Results and Discussion

As expected, increased field strength inside the newOrbitrap mass analyzer has allowed to significantlyincrease resolving power at a given acquisition time byabout 50% at the same voltage, and by 80% at anincreased voltage on the central electrode (Figure 2). Anexperimental resolving power of around 120,000 (at m/z400) has been demonstrated at 1 scan/s, which is 20%better than on a commercially available 7T FT-ICR, butstill less than the theoretical limit for 12T or 15T FT-ICR.It should be noted that due to the different dependen-cies of resolving power on mass for the different ana-lyzer types (Orbitrap versus FT-ICR), the new Orbitrapgeometry provides higher frequency and hence higherresolving power comparing to 7T and 15T FT-ICR for afixed scan duration at masses above 280 u and 1300 u,respectively (Figure 2).

526.0 526.5 527.0 527.5m/z

0.0000.0020.0040.0060.0080.0100.0120.0140.0160.0180.0200.0220.024

526.2611

527.2637

Thre

Min. peak=0.00(1 shot)

400 600 800 10000

10

20

30

40

50

60

70

80

90

100

Rel

ativ

e Ab

unda

nce

Rel

ativ

e Ab

unda

nce

Figure 3. Single full-profile spectrum acquired(monoisotopic peak at m/z 1422) and MRFA (mo[2]. Dynamic range of at least 25,000 could be ob(its theoretically predicted abundance relative to

of about 0.0035% relative to Ultramark peak at m/z 1

It was noticed that the reduced gap between the centraland the outer electrodes of the Orbitrap increases require-ments on the quality of alignment and tuning in thepreceding C-trap and ion optics. On the other hand,increase of acceleration voltage in ion optics by a factor ofabout 3 (up to 3.5 kV) improves extraction and transportof ions. This also offsets the decrease of detection effi-ciency due to the increased shielding of induced imagecurrent by the central electrode. As a result, the sensitivityof the HF Orbitrap is comparable to that of a standardOrbitrap. Experiments on maximum dynamic range in asingle shot (Figure 3) also support this statement. Usingthe multi-fill approach of the C-trap [8], a controlledmixture of ions with very high abundance differences hasbeen created, and the dynamic range in a single 0.76 sacquisition proved to exceed 25,000 comparing peaks withS/N 50,000 and S/N 2. Total target value T for the lineartrap has been T � 107, i.e., the C-trap was filled up to itscomplete saturation.

Figure 4 shows apparent shifts of frequency in fourdifferent FTMS instruments relative to measured fre-quency at a low ion load (a linear trap target value of10,000 for Orbitraps and 50,000 for FT ICR). FT ICRmass analyzer with a grid (Ultra) cell [9] has shown amarkedly different trend of frequency shifts com-pared with those with a more traditional cylindricalcell. As expected from the electrostatic nature of iontrapping in an Orbitrap analyzer (following a formalconsideration similar to that in [10]) frequency shiftsdue to space charge in any of them are substantiallym/z-independent, which contrasts with strong m/z-dependency for FT ICR or RF traps. It has also beendiscovered that these frequency shifts increase linearly

ld=0.002%

Max. peak=100%(1 shot)

200 1400 1600m/z

1421.9785

1422 1423 1424 1425 1426m/z

0

10

20

30

40

50

60

70

80

90

1001421.9785

1422.9811

1423.98431424.9873

1425.9296

Rel

ativ

e Ab

unda

nce

0.76 s for a (100%/0.3%) mixture of Ultramarkotopic peak at m/z 524) according to method ofd for minor isotope of MRFA m/z 524 at m/z 527524 is 1.2%, which results in expected intensity

528.0

sho

4%

1

fornois

servem/z

422).

1395J Am Soc Mass Spectrom 2009, 20, 1391–1396 HIGH-FIELD ORBITRAP

with the actual ion number (not shown) and even for astandard Orbitrap compare quite favorably with the high-est-field FT ICR. Deviation of Orbitrap curves of Figure 4from linear dependency is linked to the nonlinear relationbetween LT target value and the actual ion number insidethe Orbitrap: at high target values, more ions are lostduring the transfer from LT and from the C-trap due toCoulomb expansion of ion clouds in each trap and there-fore ion load stops growing at higher target values.

Surprisingly, the graph for HF Orbitrap shows a verysmall (if any) dependence on space charge even thoughtransmission to HF Orbitrap is higher than that in FTICR and similar to the standard Orbitrap. This is adirect result of a smaller gap and hence enhanced ionshielding in HF Orbitrap compared with the standardOrbitrap. This shielding effect arises because ions of thesame m/z spread in rings rotating around the centralelectrode and bouncing along it, with the central elec-trode shielding one section of the ring from anothersection. The closer central electrode comes to the ionring, the smaller is the proportion of the circumferencefor Coulomb interaction between ions. In all instru-ments considered, high mass accuracy during routinemeasurements is provided by applying an empiricalcorrection to the mass calibration with a linear depen-dency on ion load and a nonlinear dependency on m/z.Therefore, these frequency shifts and correspondingmass shifts are normally invisible to the user.

Figure 5 demonstrates that HF Orbitrap is also capableof high resolving power for intact protein analysis oncethe appropriate base pressure is achieved inside the Orbi-trap compartment using higher-temperature bake-out.Resolving power 56,000 for enolase (46 kDa) was ob-served in a 1.5 s transient using lowered voltage on thecentral electrode (2.5 kV instead of 5 kV in otherexperiments) at residual pressure 6 � 10�11 Torr. Re-duction of voltage was required to reduce center-of-mass

-8

-6

-4

-2

0

2

4

0.0E+00 5.0E+05 1.0E+06 1.5E+06 2.0E+06 2.5E+06 3.0E+06

LT Target value

Freq

uenc

y sh

ift, p

pm

Std Orbitrap

14.5 T FT ICR (cylindrical cell)

HF Orbitrap

12T LTQ FT Ultra

Figure 4. Relative Coulomb frequency shifts in HF and standardOrbitrap, 12T LTQ FT Ultra, and 14.5 T FT ICR in parts per million.Traces correspond to m/z 195, 524, 1422 in both Orbitraps, m/z 524,1422 in 12T, and m/z 524 in 14.5T FT ICR.

energy of collision between multiply-charged protein ion

and molecules of residual gas. Only then performance ofHF Orbitrap analyzer for proteins became similar to thatof a standard one which is clearly a negative effect of ionenergy increase according to (eq 7).

By careful balancing of construction tolerances andmatching electrodes to each other, it is possible toassemble an Orbitrap analyzer with much higher ulti-mate resolving power than typical for standard instru-ments. The same is applicable to HF Orbitrap as shownin Figure 6. Ultimate resolving power was obtainedusing external calibration and 3 s detection time, whichis four times longer comparing to detection time inFigure 2. Isotope clusters with fine structure wereresolved with resolving power in excess of 600,000around m/z 196, and around 380,000 m/z 525. As usualfor an optimally tuned Orbitrap, this is accompanied byhigh mass accuracy and correct isotopic ratios withineach isotopic envelope. These levels of resolving powerare still far below, and will remain below record valuesobtained in FT ICR, but it is more than adequate evenfor most demanding complex mixtures such as petro-leum or humic acids.

Conclusions

A new, high-field Orbitrap analyzer indeed provides theexpected improvement of resolving power per unit time.Through careful balancing of construction tolerances andoperation parameters, HF Orbitrap can provide maximumresolving power in excess of 350,000 at m/z 524 and600,000 at m/z 195 isotopic resolution of proteins above 40kDa and a single-shot dynamic range of 25,000. It was alsofound that mass shifts in HF Orbitrap depend very littleon space charge inside the analyzer.

At the same time, HF Orbitrap analyzer appeared tobe more demanding than a standard one with regardsto the alignment of ion optics, residual pressure, andvariations of tuning parameters. Further research anddevelopment is required to provide a robust infrastruc-

1372.5 1373.5 1374.0 1374.5 1375.0 1375.5m/z

020406080

20

4060

80100

1373.6339R=56675

1373.6334R=57445

Experimental

Theoretical

0

[M+34H]34+

[M+33H+Na]34+

Rel

ativ

e Ab

unda

nce

Rel

ativ

e Ab

unda

nce 100

Figure 5. Spectrum of yeast enolase 1 (molecular weight 46 kDa),

charge state 34� with external calibration.

o mo

1396 MAKAROV ET AL. J Am Soc Mass Spectrom 2009, 20, 1391–1396

ture and automatic procedures that would allow thisanalyzer to be used in serial instruments.

AcknowledgmentsThe authors thank Dr. Christopher Hendrickson from the NationalHigh Magnetic Field Laboratory for providing the 14.5 T FT ICRinstrument for space charge shift measurements, and Dr. MikeSenko for carrying out measurements. They also thank ProfessorNeil Kelleher for providing data from 12 T LTQ FT Ultra instru-ment. The authors are grateful to Wilko Balschun for mechanicaldesign of HF Orbitrap construction, Alexander Kholomeev fordeveloping electronics for experiments, Dr. Jens Griep-Ramingand Dr. Stevan Horning for support and fruitful discussions. Theresearch leading to these results has received funding from theEuropean Commission’s 7th Framework Programme (grant agree-ment HEALTH-F4-2008-201648/PROSPECTS).

References1. Marshall, A. G.; Guan, S. Advantages of High Magnetic Field for

523 5240

10

20

30

40

50

60

70

80

90100

524.265

0

1

2

3

4

0

1

2

3

4

Rel

ativ

e A

bund

ance

196.06 196.08 196.10 196.120

2

4

6

8

10

12

0

2

4

68

10

12196.0913R=630118

196.0850R=598468

196.0910R=629410

196.0847R=629316

195.0 196.00

10

20

30

40

50

60

70

80

90

100

195.088R=621788

196.091R=629203

Rel

ativ

e Ab

unda

nce

200 400 600

195.088

524.265262.636

RFWHM ≈630,000 @ m/z 195

Figure 6. Ultimate resolving power obtained uto detection time in Figure 2) and EXTERNALpanels for corresponding m/z. Isotope clusters wcorresponding theoretical patterns normalized t

Fourier Transform Ion Cyclotron Resonance Mass Spectrometry. RapidCommun. Mass Spectrom. 1996, 10(14), 1819–1823.

2. Marshall, A. G.; Hendrickson, C. L.; Jackson, G. S. Fourier TransformIon Cyclotron Resonance Mass Spectrometry: A Primer. Mass Spectrom.Rev. 1998, 17, 1–35.

3. Makarov, A. Electrostatic Axially Harmonic Orbital Trapping: A High-Performance Technique of Mass Analysis. Anal. Chem. 2000, 72, 1156–1162.

4. Makarov, A.; Denisov, E.; Kholomeev, A.; Balschun, W.; Lange, O.;Horning, S.; Strupat, K. Performance Evaluation of a Hybrid Linear IonTrap/Orbitrap Mass Spectrometer. Anal. Chem. 2006, 78, 2113–2120.

5. Wenger, C. D.; Boyne, M. T.; Ferguson, J. T.; Robinson, D. E.; Kelleher,N. L. Versatile Online-Offline Engine for Automated Acquisition ofHigh-Resolution Tandem Mass Spectra. Anal. Chem. 2008, 80, 8055–8063.

6. Schaub, T. M.; Hendrickson, C. L.; Horning, S.; Quinn, J. P.; Senko,M. W.; Marshall, A. G. High-Performance Mass Spectrometry: FourierTransform Ion Cyclotron Resonance at 14.5 Tesla. Anal. Chem. 2008, 80,3985–3990.

7. Schwartz, J. C.; Senko, M. W.; Syka, J. E. P. A Two-DimensionalQuadrupole Ion Trap Mass Spectrometer. J. Am. Soc. Mass Spectrom.2002, 13, 659–669.

8. Makarov, A.; Denisov, E.; Lange, O.; Horning, S. Dynamic Range ofMass Accuracy in LTQ Orbitrap Hybrid Mass Spectrometer. J. Am. Soc.Mass Spectrom. 2006, 17, 977–982.

9. Wieghaus A., Froehlich U., Malek R., Horning S. The Grid Cell: A NewCell Design for Reduced Z-Axis Ejection in Fourier Transform IonCyclotron Mass Spectrometry. Proceedings of the 54th ASMS Conference;Seattle, WA, May, 2006.

10. Jeffries, J. B.; Barlow, S. E.; Dunn, G. H. Theory of Space-Charge Shifts

526 527/z

68

526.261 527.2641522.0 1523.0 1524.0 1525.0

m/z

0

10

20

30

40

50

60

70

80

90

100

1521.972R=238701

1522.976R=239700

1523.979R=228604

526.26 526.28 526.30m/z

526.2614R=377733

526.2722R=375264

526.2756R=354997

526.2608R=378620

526.2717R=375454

526.2747R=359061

Experimental

RFWHM ≈380,000 @ m/z 524

0 1000 1200 1400 1600 1800 2000

m/z

1421.9781221.991 1621.965

1721.9591121.9971821.9531022.004

Theoretical

RFWHM ≈230,000 @ m/z 1522

3 s detection time (four times longer comparingbration. Experimental values are presented onine structure are presented in insets along withnoisotopic peak.

525m

525.2

80

singcali

ith f

of Ion Cyclotron Resonance Frequencies. Int. J. Mass Spectrom IonProcesses 1983, 54, 169–187.