Ion/molecule reactions, mass spectrometry and optical spectroscopy in a linear ion trap

Welling, Michael; Schuessler, H. A.; Thompson, R. I.; Walther, H.

doi:10.1016/s0168-1176(97)00251-6

Cited by 69 publications

(39 citation statements)

References 26 publications

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“…Various different trap technologies are also being considered. Fluorescence detection of ions stored in a linear quadrupole [26] would reduce the laser scattering from trap electrodes yet provide fluorescence collection from a larger laser-cloud interaction volume. Cylindrical ion traps [27,28] offer the possibility to detect through a ring electrode formed from highly transparent (ϳ80%) Ni screen.…”

Section: Discussionmentioning

confidence: 99%

Pulsed fluorescence measurements of trapped molecular ions with zero background detection

Khoury¹,

Rodriguez‐Cruz²,

Parks³

2002

J Am Soc Mass Spectrom

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Sensitive methods have been developed to measure laser-induced fluorescence from trapped ions by reducing the detection of background scattering to zero levels during the laser excitation pulse. The laser beam diameter has been reduced to ϳ150 m to eliminate scattering on trap apertures and the resulting laser-ion interaction is limited to a volume of ϳ10 Ϫ5 cm 3 which is ϳ0.03-0.15 of the total ion cloud volume depending on experimental conditions. The detection optics collected fluorescence only from within the solid angle defined by laser-ion interaction volume. Rhodamine 640 and Alexa Fluor 350 ions, commonly used as fluorescence resonance energy transfer (FRET) fluorophores, were generated in the gas phase by using electrospray ionization and injected into a radiofrequency Paul trap where they were stored and exposed to Nd:YAG laser pulses at 532 and 355 nm for times up to 10 m. Fluorescence emitted by these ions was investigated for several trap q z values and ion cloud temperatures. Analysis of photon statistics indicated an average of ϳ10 photons were incident on the PMT detector per 15 ns pulse for ϳ10 3 trapped ions in the interaction volume. Fluorescence measurements displayed a dependence on trapped ion number which were consistent with calculations of the space charge limited ion density. To investigate the quantitative capability of these fluorescence techniques, the laser-induced fragmentation of trapped Alexa I on traps provide a controlled environment in which fluorescence measurements can be performed on an ensemble of ions over timescales sufficient to consider small ion numbers and slow reaction rates. Laserinduced fluorescence measurements of trapped ions have been used in spectroscopic studies of atomic structure [1][2][3][4], the vibrational spectra of small molecules [5][6][7][8], as well as to characterize the dynamic cooling [9] and crystallization of atomic ions [10 -12].This paper introduces techniques that eliminate the detection of laser background scattering on trap apertures and internal surfaces allowing measurements to achieve both high sensitivity and large dynamic range. In previous pulsed laser measurements of molecular fluorescence collected from trapped species (discussed in references [5][6][7][8]), the radiative lifetimes were sufficiently long to allow collection of fluorescence radiation after the laser pulse. This greatly simplified methods to reduce the detection of background resulting from scattered laser radiation. However, experiments described in this paper apply the Nd:YAG pulsed laser to excite strongly emitting molecules having fluorescence lifetimes shorter than the laser pulse. This required the reduction of background laser scattering during laser excitation, a more demanding constraint.Techniques described in this paper will help to extend fluorescence measurements as an in situ probe of trapped ion properties including chemical identity, the growth and decay of specific ion populations, ion spectroscopy. Fluorescence emission from trapped ions also presen...

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Section: Discussionmentioning

confidence: 99%

Pulsed fluorescence measurements of trapped molecular ions with zero background detection

Khoury¹,

Rodriguez‐Cruz²,

Parks³

2002

J Am Soc Mass Spectrom

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“…Welling and co-workers used this method, which they termed "secular scanning", to obtain higher resolution mass spectra when compared to q scanning in a linear ion trap (the resonance was quadrupolar over a limited mass range and with slow frequency scanning) [27], Roth and coworkers used secular frequency scanning in a linear trap for mass selective excitation [28], and the Austin group at Brigham Young University used it to scan ions out of the halo ion trap [29][30][31]. Note that in the case of the halo trap, the geometry of the device necessitated the use of AC frequency scanning because simulations indicated that a conventional rf amplitude ramp would cause ions to collide with the electrodes and ceramic holders instead of being ejected out the apertures in the electrodes.…”

Section: Introductionmentioning

confidence: 99%

Experimental Characterization of Secular Frequency Scanning in Ion Trap Mass Spectrometers

Snyder

Pulliam

Wiley

et al. 2016

J. Am. Soc. Mass Spectrom.

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Abstract. Secular frequency scanning is implemented and characterized using both a benchtop linear ion trap and a miniature rectilinear ion trap mass spectrometer. Separation of tetraalkylammonium ions and those from a mass calibration mixture and from a pesticide mixture is demonstrated with peak widths approaching unit resolution for optimized conditions using the benchtop ion trap. The effects on the spectra of ion trap operating parameters, including waveform amplitude, scan direction, scan rate, and pressure are explored, and peaks at black holes corresponding to nonlinear (higher-order field) resonance points are investigated. Reverse frequency sweeps (increasing mass) on the Mini 12 are shown to result in significantly higher ion ejection efficiency and superior resolution than forward frequency sweeps that decrement mass. This result is accounted for by the asymmetry in ion energy absorption profiles as a function of AC frequency and the shift in ion secular frequency at higher amplitudes in the trap due to higher order fields. We also found that use of higher AC amplitudes in forward frequency sweeps biases ions toward ejection at points of higher order parametric resonance, despite using only dipolar excitation. Higher AC amplitudes also increase peak width and decrease sensitivity in both forward and reverse frequency sweeps. Higher sensitivity and resolution were obtained at higher trap pressures in the secular frequency scan, in contrast to conventional resonance ejection scans, which showed the opposite trend in resolution on the Mini 12. Mass range is shown to be naturally extended in secular frequency scanning when ejecting ions by sweeping the AC waveform through low frequencies, a method which is similar, but arguably superior, to the more usual method of mass range extension using low q resonance ejection.

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“…Although promising results were presented, space charge effects were found to limit this configuration's ultimate performance as the motion of the ions is largely restricted to one of the symmetry planes of the device. The relative insensitivity of the image current ion detection scheme precluded the use of lower numbers of trapped ions to avoid such space charge effects.Welling et al demonstrated two variations of mass selective instability in a stand-alone 2-D quadrupole ion trap [18]. The first method, referred to as "q-scanning", exploited the field penetration of the detector between the quadrupole rods to allow for ion extraction using a downward ramp of the RF voltage.…”

mentioning

confidence: 99%

“…Welling et al demonstrated two variations of mass selective instability in a stand-alone 2-D quadrupole ion trap [18]. The first method, referred to as "q-scanning", exploited the field penetration of the detector between the quadrupole rods to allow for ion extraction using a downward ramp of the RF voltage.…”

mentioning

confidence: 99%

A two-dimensional quadrupole ion trap mass spectrometer

Schwartz

Senko

Syka

2002

J. Am. Soc. Mass Spectrom.

674

718

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The use of a linear or two-dimensional (2-D) quadrupole ion trap as a high performance mass spectrometer is demonstrated. Mass analysis is performed by ejecting ions out a slot in one of the rods using the mass selective instability mode of operation. Resonance ejection and excitation are utilized to enhance mass analysis and to allow isolation and activation of ions for MS n capability. Improved trapping efficiency and increased ion capacity are observed relative to a three-dimensional (3-D) ion trap with similar mass range. Mass resolution comparable to 3-D traps is readily achieved, including high resolution at slower scan rates, although adequate mechanical tolerance of the trap structure is a requirement. [8 -11], and standard three-dimensional (3-D) ion trap mass spectrometers [12,13]. Several of the quadrupole based 2-D ion traps are capable of mass selective isolation and activation of ions including MS 3 analysis [7,9 -11]. Syka and Fies have described the theoretical advantages of 2-D versus 3-D quadrupole ion traps for Fourier transform mass spectrometry [14]. These advantages include reduced space charge effects due to the increased ion storage volume, and enhanced sensitivity for externally injected ions due to higher trapping efficiencies. Bier and Syka described several forms of linear and circular 2-D ion traps with larger ion capacity to be used as mass spectrometers [15] using the mass selective instability mode of operation [16] similar to that used in all commercial 3-D quadrupole ion trap instruments.Despite the previously described advantages and the recent progress with 2-D ion traps in hybrid instruments, only a few examples have appeared using these traps as stand-alone mass spectrometers. Senko et al. recently demonstrated image current detection with FT analysis in a 2-D ion trap which utilized independent detection electrodes between the quadrupole rods [17]. Although promising results were presented, space charge effects were found to limit this configuration's ultimate performance as the motion of the ions is largely restricted to one of the symmetry planes of the device. The relative insensitivity of the image current ion detection scheme precluded the use of lower numbers of trapped ions to avoid such space charge effects.Welling et al. demonstrated two variations of mass selective instability in a stand-alone 2-D quadrupole ion trap [18]. The first method, referred to as "q-scanning", exploited the field penetration of the detector between the quadrupole rods to allow for ion extraction using a downward ramp of the RF voltage. This allowed relatively quick scanning of a broad mass range (1 second scan from 20 -1000 m/z), but produced mass spectral resolution of only five to six. The second method, referred to as "secular scanning", used frequency swept parametric excitation to eject ions between the quadrupole rods. Although the scan rate was 100x slower than the q-scan, a resolution of 800 at m/z 130 was obtained.Lammert et al. have presented preliminary results using a toroida...

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Ion/molecule reactions, mass spectrometry and optical spectroscopy in a linear ion trap

Cited by 69 publications

References 26 publications

Pulsed fluorescence measurements of trapped molecular ions with zero background detection

Pulsed fluorescence measurements of trapped molecular ions with zero background detection

Experimental Characterization of Secular Frequency Scanning in Ion Trap Mass Spectrometers

A two-dimensional quadrupole ion trap mass spectrometer

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