Model independent peak fitting and uncertainty assignment for high-precision time-of-flight mass spectrometry.

A procedure is introduced to extract the time-of-flight probability density distribution for ions of one type using an accumulated ion peak as a template for use in the fitting of time-of-flight peaks of co-accumulated ions. We demonstrate the use of logarithmic splines and discuss the statistical criteria for the selection of the spline smoothing parameter to obtain a smooth function for approximating such an ion peak. Furthermore, a "Bootstrap" method is proposed to determine the uncertainty of the fitted time-of-flight values, which is calculated using the extracted peak shape via a repeated statistical experiment. The developed procedure is validated against time-of-flight data obtained in a previously reported experiment. It is shown that atomic masses derived from our newly proposed methodology are in good agreement with those from the 2016 Atomic Mass Evaluation and the values determined using an analytically defined function (exponential-Gaussian hybrid), approximately matching the observed peak shape. In contrast to the previously used approach, our newly proposed methodology is a much more flexible, robust, and universal method for peak shape approximation, which can be applied to any peak shape.

Low-mobility-pass filter between atmospheric pressure chemical ionization and electrospray ionization sources and a single quadrupole mass spectrometer: computational models and measurements.

RATIONALE: Mixtures of ions produced in sources at atmospheric pressure, including chemical ionization (APCI) and electrospray ionization (ESI) can be simplified at or near ambient pressure using ion mobility based filters. METHODS: A low-mobility-pass filter (LMPF) based on a simple mechanical design and simple electronic control was designed, modeled and tested with vapors of 2-hexadecanone in an APCI source and with spray of peptide solutions in an ESI source. The LMPF geometry was planar and small (4 mm wide × 13 mm long) and electric control was through a symmetric waveform in low kHz with amplitude between 0 and 10 V. RESULTS: Computational models established idealized performance for transmission efficiency of ions of several reduced mobility coefficients over the range of amplitudes and were matched by computed values from ion abundances in mass spectra. The filter exhibited a broad response function, equivalent to a Bode Plot in electronic filters, suggesting that ion filtering could be done in blocks ~50 m/z units wide. CONCLUSIONS: The benefit of this concept is that discrimination against ions of high mobility is controlled by only a single parameter: waveform amplitude at fixed frequency. The effective removal of high mobility ions, those of low mass-to-charge, can be beneficial for applications with ion-trap-based mass spectrometers to remove excessive levels of solvent or matrix ions.