Electron ionization LC‐MS with supersonic molecular beams—the new concept, benefits and applications

Abstract

A new type of electron ionization LC-MS with supersonic molecular beams (EI-LC-MS with SMB) is described. This system and its operational methods are based on pneumatic spray formation of the LC liquid flow in a heated spray vaporization chamber, full sample thermal vaporization and subsequent electron ionization of vibrationally cold molecules in supersonic molecular beams. The vaporized sample compounds are transferred into a supersonic nozzle via a flow restrictor capillary. Consequently, while the pneumatic spray is formed and vaporized at above atmospheric pressure the supersonic nozzle backing pressure is about 0.15 Bar for the formation of supersonic molecular beams with vibrationally cold sample molecules without cluster formation with the solvent vapor. The sample compounds are ionized in a fly-though EI ion source as vibrationally cold molecules in the SMB, resulting in 'Cold EI' (EI of vibrationally cold molecules) mass spectra that exhibit the standard EI fragments combined with enhanced molecular ions. We evaluated the EI-LC-MS with SMB system and demonstrated its effectiveness in NIST library sample identification which is complemented with the availability of enhanced molecular ions. The EI-LC-MS with SMB system is characterized by linear response of five orders of magnitude and uniform compound independent response including for non-polar compounds. This feature improves sample quantitation that can be approximated without compound specific calibration. Cold EI, like EI, is free from ion suppression and/or enhancement effects (that plague ESI and/or APCI) which facilitate faster LC separation because full separation is not essential. The absence of ion suppression effects enables the exploration of fast flow injection MS-MS as an alternative to lengthy LC-MS analysis. These features are demonstrated in a few examples, and the analysis of the main ingredients of Cannabis on a few Cannabis flower extracts is demonstrated. Finally, the advantages of EI-LC-MS with SMB are listed and discussed.

Second hydrogen atom abstraction by molecular ions

“…We also explored the second hydrogen atom abstraction by molecular ions phenomenon with our EI‐LC‐MS with SMB system that served for the direct introduction of liquids and solutions for their EI‐MS analysis. Our EI‐LC‐MS with SMB system is described in details in . Briefly, the system is designed to vaporize steady flow of liquid at atmospheric pressure by the formation of pneumatic assisted spray followed by a capillary flow restrictor and supersonic nozzle.…”

“…Our general research is focused on the development of GC‐MS with supersonic molecular beams (SMB) which is also known as GC‐MS with cold electron ionization (EI), and EI LC‐MS with SMB . We also developed a method of cluster chemical ionization (CCI) in which we add methanol vapor to the helium make‐up gas of the SMB which can form methanol clusters with sample compound hence increase the relative abundance of the molecular ion and of protonated sample molecules plus sometime also form clusters of the molecular ions with methanol.…”

MS-Based Analytical Techniques: Advances in Spray-Based Methods and EI-LC-MS Applications

“…Over the past years, Seemann and his group developed the supersonic molecular beams (SMB) LC-MS interface [ 34 ]. Their studies started from the knowledge that standard emission energy (70 eV) used in EI is not ideal for many NIST library compounds that have a weak (below 2% relative abundance) or no molecular ion.…”

“…A third group of researchers, headed by Rigano, presented a new nano-LC-EI-MS for the determination of free fatty acids (FFAs) in mussels [ 34 ]. A selective and sensitive nano-LC-EI-MS analytical method to investigate the FFA profile in marine organisms and to monitor marine sentinels for the assessment of environmental pollution effects was developed [ 35 ].…”

Recent Analytical Approaches in Quality Control of Cannabis sativa L. and Its Preparations

“…MALDI-MS is another technique capable of detecting low-level cannabinoids, though in this case, also requiring derivatization (Beasley et al, 2016); 200 samples were analyzed using Infrared and Raman screening of seized novel psychoactive substances (Jones et al, 2016); Evaluating the selectivity of colorimetric test (Fast Blue BB salt) for the cannabinoids identification in marijuana street samples by UV-Vis, TLC, ESI (+) FT-ICR MS and ESI (+) MS/MS (dos Santos et al, 2016). By the year 2015-Compact Mass Spectrometry was used for Detection and Quantitation of Cannabis-Related Compounds (Jack and Henion, 2015); By HILIC, as part of an RP-HPLC study for the determination of the cannabinoids in cannabis and a marijuana concentrate (Hung et al, 2015); By 2D-LC with chemiluminescence detection, for screening of cannabinoids in industrial-grade hemp (Pandohee et al, 2015); By EI-LC/MS with supersonic molecular beams (an introductory technique study, including cannabis) (Seemann et al, 2015).…”