Broad-Band Fourier Transform Quadrupole Ion Trap Mass Spectrometry

Abstract

Broad-band nondestructive ion detection is achieved in a quadrupole ion trap mass spectrometer by impulsive excitation of a collection of trapped ions of different masses and recording of ion image currents induced on a small detector electrode embedded in but isolated from the adjacent end cap electrode. The image currents are directly measured using a simple differential preamplifier, filter, and amplifier combination and then Fourier analyzed to obtain broad-band frequency domain spectra characteristic of the sample ions. The use of the detector electrode provides a significant reduction in capacitive coupling with the ring electrode. This minimizes coupling of the rf drive signal, which can saturate the front-end stage of the detection circuit and prevent measurement of the relatively weaker ion image currents. Although impulsive excitation is preferred due to its broad-band characteristics and simplicity of use, results are also given for narrow-band ac and broad-band SWIFT (stored wave-form inverse Fourier transform) excitation. Data using argon, acetophenone, and n-butylbenzene show that a resolution of better than 1000 is obtained with a detection bandwidth of 400 kHz. An advantage of nondestructive ion detection is the ability to measure a single-ion population multiple times. This is demonstrated using argon as the sample gas with an average remeasurement efficiency of >90%. Tandem mass spectrometry experiments using a population of acetophenone ions are also shown.

Orbitrap mass spectrometry: Instrumentation, ion motion and applications

“…Fast FT-based image current detection of ion axial motion has been previously demonstrated in 3D quadrupole (Badman et al, 1999;Goeringer, Crutcher, & McLuckey, 1995;Parks, Pollack, & Hill, 1994;Soni et al, 1996;Syka & Fies, 1988) and cylindrical ion traps (Badman et al, 1998), as well as the ICR cell (Schweikhard et al, 1989). The commercial orbitrap mass spectrometer has the following performance characteristics: (i) mass resolution up to 150,000, (ii) mass accuracy of 2-5 ppm (internal and external calibration, respectively), (iii) an ion abundance range of 1:5,000 over which accurate mass measurements can be made (''extent of mass accuracy''), (iv) as good as 0.2 ppm mass accuracy for peaks with signal-to-noise (S/N) ratio >10,000, (v) published upper mass-to-charge (m/z) limit of at least 6,000, (vi) increased spacecharge capacity at higher masses due to independence of the trapping potential on m/z ratio, (vii) in-spectrum linear dynamic range up to four orders of magnitude and (viii) larger trapping capacity compared to FT-ICR and the 3-D Paul trap (Hardman & Makarov, 2003;Hu et al, 2005;Makarov, 2000;Makarov et al, 2006a,b).…”

Characterization of a hybrid ion trap

“…Our conclusion is that modification of the ring electrode geometry affects the a z and q z parameters describing the ion stability boundary, yet has no apparent effect on the basic properties of the ion trap of linear mass scan, effective isolation and unit mass resolution. Currently the hybrid ion trap is being studied as a candidate for in situ image current detection [28,29]. Future work includes the optimization of the cell geometry for increased ion capacity.…”

Metabolism of Fluazifop-P-butyl in Resistant Goosegrass (Eleusine indica) in Taiwan

“…Since the ions are not destroyed, they can be remeasured. A non-destructive method of ion detection (20) is achieved in ion traps by impulsive excitation of a collection of trapped ions, typically of different m/z values. The ion image currents are induced on a small detector electrode embedded in, but isolated from, the end-cap electrode.…”