A Hadamard transform electron ionization time-of-flight mass spectrometer

Abstract

We describe the first Hadamard transform time-of-flight mass spectrometer (HT-TOFMS) that incorporates an electron (impact) ionization source. This implementation was realized in an existent TOF instrument using commercially available components and simple modifications to the ion source. In the present apparatus, a Hadamard mask is expressed by modulating the ion generation process within the ion source; thus, the present approach differs from previous designs that use external electrostatic devices to modulate a continuous ion stream. The present implementation may be operated in conventional TOF mode at 12.5 kHz and in HT-TOF mode at 20-40 MHz. In Hadamard mode the design can operate using any circulant simplex code, allowing the operator much flexibility for optimizing resolution and mass range and for eliminating nonstochastic fluctuations, e.g., encoding errors and signal hum. We demonstrate typical performance of the HT-TOFMS in standard and reflectron geometries using sequences of three constructions and of varied length, generating HT-TOF mass spectra of molecules that match conventional reference spectra. The auxiliary material includes an electrical schematic for the floating high-speed encoding amplifier, which is also of use in other high-speed electrostatic optics applications, and a list of 537 validated vectors comprising the first row of each circulant simplex sequence (S(n)=3-8219) derived using maximal shift register (n=2(m)-1), quadratic residue (n=4m-3), and twin prime constructions [n=p(p+2)].

Rapid identification of false peaks in the spectrum of Hadamard transform ion mobility spectrometry with inverse gating technique

“…In addition, different constructions of PRBS would lead to different positions and intensities of the false peaks, which made the identication and reduction of the false peaks more complicated. 32 Clowers et al 25 presented the "doubling" method, which could partially correct the distortion of the HT-IMS. Kwasnik et al 28 developed an extended HT technique, which achieved the reduction of the false peaks in the demultiplexed data signicantly.…”

Digitally-Multiplexed Nanoelectrospray Ionization Atmospheric Pressure Drift Tube Ion Mobility Spectrometry

“…Hadamard multiplexing was originally developed for optical spectroscopies where the involved photons travel at speeds orders of magnitude larger than the modulation rates; however, when the injection of ions traveling under atmospheric pressure conditions is multiplexed, the involved species have much lower velocities and may experience depletion between closely spaced gating events, along with thermal or space-charge induced diffusion along the longitudinal and radial axes of the drift region. The identification of modulation defects and the reduction of their effects are further complicated by the dependency of their position and intensity on the different possible PRS constructions, as demonstrated by Hudgens et al…”

Recent Advances in Instrumental Approaches to Time‐of‐flight Mass Spectrometry

“…Here, HT‐TOFMS has been shown to improve peak‐height precision, that is, peak height relative standard deviation (RSD), as compared to conventional TOFMS by a factor of ( N /2) 1/2 , an advantage particularly important for ions of low abundance (Kimmel et al, 2005). In 2008, Hudgens and Bergeron described an electron ionization Hadamard transform TOFMS.…”