From the discovery of field ionization to field desorption and liquid injection field desorption/ionization-mass spectrometry—A journey from principles and applications to a glimpse into the future

Abstract

<jats:p> The discovery of the ionizing effect of strong electric fields in the order of volts per Ångstrom in the early 1950s eventually led to the development of field ionization-mass spectrometry (FI-MS). Due to the very low ion currents, and thus, limited by the instrumentation of the 1960s, it took some time for the, by then, new technique to become adopted for analytical applications. In FI-MS, volatile or at least vaporizable samples mainly deliver molecular ions, and consequently, mass spectra showing no or at least minor numbers of fragment ion signals. The next major breakthrough was achieved by overcoming the need to evaporate the analyte prior to ionization. This was accomplished in the early 1970s by simply depositing the samples onto the field emitter and led to field desorption-mass spectrometry (FD-MS). With FD-MS, a desorption ionization method had become available that paved the road to the mass spectral analysis of larger molecules of low to high polarity and even of organic salts. In FD-MS, all of these analytes deliver spectra with no or at least few fragment ion peaks. The last milestone was the development of liquid injection field desorption/ionization (LIFDI) in the early 2000s that allows for sample deposition under the exclusion of atmospheric oxygen and water. In addition to sampling under inert conditions, LIFDI also enables more robust and quicker operation than classical FI-MS and FD-MS procedures. The development and applications of FI, FD, and LIFDI had mutual interference with the mass analyzers that were used in combination with these methods. Vice versa, the demand for using these techniques on other than magnetic sector instruments has effectuated their adaptation to different types of modern mass analyzers. The journey started with magnetic sector instruments, almost skipped quadrupole analyzers, encompassed Fourier transform ion cyclotron resonance (FT-ICR) and orthogonal acceleration time-of-flight (oaTOF) analyzers, and finally arrived at Orbitraps. Even interfaces for continuous-flow LIFDI have been realized. Even though being niche techniques to some degree, one may be confident that FI, FD, and LIFDI have a promising future ahead of them. This Account takes you on the journey from principles and applications of the title methods to a glimpse into the future. </jats:p>

Molecular Characterization of Heavy Petroleum by Mass Spectrometry and Related Techniques

“…These molecules cannot be effectively ionized by APPI due to their higher ionization potentials nor by ESI due to their low polarity. Field ionization/field desorption (FI/FD) have shown to be highly effective for ionizing saturates when used in conjunction with a time-of-flight (TOF) mass spectrometer ,,,− but have not been successful when used in coupling with FT-ICR MS. Severe fragmentation was observed, most likely due to the short life span of the molecule ions and long ion accumulation time in the FT-ICR operations .…”

Negative-ion field desorption revitalized by using liquid injection field desorption/ionization-mass spectrometry on recent instrumentation

“…Field ionization (FI) and field desorption (FD) are very soft ionization techniques in mass spectrometry that generally deliver intact positive molecular ions, M +• , or adduct ions like [M+H] + or [M+alkali] + of molecular analytes [1][2][3][4]. In case of ionic compounds, FD and liquid injection field desorption/ ionization (LIFDI) spectra reveal the intact cations C + , often accompanied by cluster ions [C n+1 A n ] + .…”

“…In the light of more recent instrumentation and the improvements of the technique as provided by the advent of LIFDI [24][25][26][27][28][29][30][31], we have revisited negative-ion FD-MS by using the LIFDI setup on two different instrumental platforms. In contrast to the classic implementation of FD, the LIFDI setup offers the additional advantage of sample application to the emitter under the complete exclusion of moisture and air [4,28,29,[32][33][34][35][36][37]. Here, we demonstrate the application of negative-ion LIFDI mode on both a JEOL AccuTOF GCx and a Waters Micromass Q-TOF Premier instrument to a variety of samples.…”

Nontargeted Screening Using Gas Chromatography–Atmospheric Pressure Ionization Mass Spectrometry: Recent Trends and Emerging Potential

“…However, extensive fragmentation under EI conditions can also produce mass spectra in which the molecular ion is absent, thereby confounding elemental composition determination and structure elucidation. This drawback can potentially be solved by lowering the electron energy in EI or using other vacuum ionization techniques such as chemical ionization (CI) [10], photoionization (PI) [11] and field ionization (FI) [12], which impart significantly less energy to the analyte molecules. The past 30 years have also witnessed the advent of atmospheric pressure ionization techniques and (hybrid) mass analyzers, whose development was primarily driven by the need for LC-MS and direct analysis applications.…”