LC–MS with electron ionization of cold molecules in supersonic molecular beams

“…Typically, relatively simple mass spectra are obtained, with intense molecular ion signals [25]. Several researchers have been developing approaches to ionize trace level analytes directly from liquids using EI, including molecular beam based interfaces by the Amirav group [26,27] and direct EI (DEI) by the Cappiello group [28][29][30]. With DEI, a low flow of liquid carrier is admitted directly to a heated EI source under high vacuum.…”

mentioning

confidence: 99%

Condensed Phase Membrane Introduction Mass Spectrometry with Direct Electron Ionization: On-line Measurement of PAHs in Complex Aqueous Samples

Termopoli

Famiglini

Palma

et al. 2015

J. Am. Soc. Mass Spectrom.

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Abstract. Polycyclic aromatic hydrocarbons (PAHs) are USEPA regulated priority pollutants. Their low aqueous solubility requires very sensitive analytical methods for their detection, typically involving preconcentration steps. Presented is the first demonstrated 'proof of concept' use of condensed phase membrane introduction mass spectrometry (CP-MIMS) coupled with direct liquid electron ionization (DEI) for the direct, on-line measurement of PAHs in aqueous samples. DEI is very well suited for the ionization of PAHs and other nonpolar compounds, and is not significantly influenced by the co-elution of matrix components. Linear calibration data for low ppb levels of aqueous naphthalene, anthracene, and pyrene is demonstrated, with measured detection limits of 4 ppb. Analytical response times (t 10%-90% signal rise) ranged from 2.8 min for naphthalene to 4.7 min for pyrene. Both intra-and interday reproducibility has been assessed (<3% and 5% RSD, respectively). Direct measurements of ppb level PAHs spiked in a variety of real, complex environmental sample matrices is examined, including natural waters, sea waters, and a hydrocarbon extraction production waste water sample. For these spiked, complex samples, direct PAH measurement by CP-MIMS-DEI yielded minimal signal suppression from sample matrix effects (81%-104%). We demonstrate the use of this analytical approach to directly monitor real-time changes in aqueous PAH concentrations with potential applications for continuous on-line monitoring strategies and binding/adsorption studies in heterogeneous samples.

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“…An additional important beneficial feature of EI‐LC‐MS with SMB is that its response is linear unlike that of the Particle Beam. In a previous publication we demonstrated over 4 orders of magnitude linear dynamic range (LDR) for pyrene with linear correlation coefficient R = 0.9993 (as shown in Fig. in that publication) and in our current system our LDR is five orders of magnitude from the limit of detection which is about 1 pg in SIM mode to about 1 µg and the main limitation is in the proper adjustment of the ion detector gain within its limited dynamic range.…”

Section: Results—cold Ei Mass Spectra Features and Selected Applicatmentioning

confidence: 73%

“…Vaporized solvent molecules served as the SMB carrier gas without adding another seeding gas. LC‐MS with SMB was experimentally evaluated for a broad range of thermally labile and relatively large compounds in liquids, and it generated the following main advantages: (1) Library searchable EI mass spectra are provided for positive sample compounds identification, combined with enhanced molecular ions for improved confidence level in the identification; (2) Non‐polar compounds are amenable for analysis in addition to the standard range of APCI compounds; (3) Approximately uniform compound independent response was obtained which enables easier sample quantitation even for unknown samples. (4) Matrix related ion suppression effects do not exist.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2015

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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.

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LC–MS with electron ionization of cold molecules in supersonic molecular beams

Cited by 35 publications

References 41 publications

Mass spectrometry for the identification of the discriminating signals from metabolomics: Current status and future trends

Mass spectrometry for the identification of the discriminating signals from metabolomics: Current status and future trends

Condensed Phase Membrane Introduction Mass Spectrometry with Direct Electron Ionization: On-line Measurement of PAHs in Complex Aqueous Samples

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

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