Signal Enhancement by Crossing the Sample Flow at a Small Angle against the Laser Beam in Multiphoton Ionization Mass Spectrometry

Abstract

To enhance sensitivity in multiphoton ionization/time-of-flight mass spectrometry, the sample, in the form of an effusive molecular flow, was introduced at a small angle relative to the laser beam. This approach enlarged the volume of interaction between the sample and the laser beam, thus increasing the number of ions formed by multiphoton ionization. The sensitivity obtained using this technique was compared with that obtained using a previous method based on the off-axis sample introduction technique with detection limits for organic hydrocarbons at the subfemtogram level. The detection limit was examined for dioxins and an improvement of 2.5 ± 0.4 fold was found. The technique developed herein is applicable for practical ultratrace analysis of persistent organic pollutants.

Femtosecond ionization mass spectrometry for chromatographic detection

“…ΔEexcess, excess energy; M + , molecular ion: F + , fragment ion; F, neutral fragment; S0, ground state; S1, excited state (reproduced from ref. [22], with permission from the Royal Society of Chemistry). (reproduced from ref.…”

“…The measured mass resolution was 1,600 [21]. The efficiency of ionization can be improved by 2.5 fold by introducing the molecular beam at the angle slightly off-axis with respect to the laser beam [22].…”

Detection limits of organic compounds achievable with intense, short-pulse lasers

“…While these types of laser systems are still mostly found in research labs, user friendly short pulse fibre and disc laser systems are approaching similar specifications. 55 With further optimization of the laser-gas interaction geometry 56 which could include multiple reflections of the laser through the target, these detection sensitivities could be reached with current commercial lasers which are compact, rugged, and modestly priced.…”

Multiphoton ionization mass spectrometry of nitrated polycyclic aromatic hydrocarbons

“…The analytical instrument used in this study has been described in detail elsewhere [24,25]. Briefly, a GC (6890GC, Agilent technologies) equipped with an auto sampler (6890N, Agilent technologies) was combined with a TOF-MS developed in our laboratory and now commercially available (HGK-1, Hikari-GK, Fukuoka, Japan).…”