Multiphoton Ionization and Circular Dichroism: New Experimental Approach and Application to Natural Products

Abstract

Enantio-sensitive laser mass spectrometry is the combination of multiphoton ionization by circularly polarized laser light with mass spectrometric detection of ions. The method has been developed as a tool for the fast investigation of chiral molecules in sample mixtures without any preceding separation and offers many new experimental possibilities. The main difficulties of the detection of circular dichroism in this way arise from systematic and statistical deviations. Herein, we report the newest approach to overcome these problems using a so-called twin-peak ion source, back-reflection of the laser light, and reference substances. By these means, the detection limit for circular dichroism can be lowered from the percent to the per-mill range. The capabilities of the new setup are demonstrated by the investigation of several natural products.

Photoionization and photofragmentation in mass spectrometry with visible and UV lasers

“…Already small fluctuations lead to large variations in the final ion yields for left‐ and right‐circularly polarized light. In 2009, the Boesl group addressed this problem by introducing a so called twin‐peak ion source to their experimental setup (Logé et al, ; see also Logé & Boesl, ). The main idea behind this special ion source is to measure both ion signals during the same laser pulse.…”

“…Ionizing the chiral sample and the achiral or racemic reference substance, under the same conditions, within the same laser pulse gives rise to reference peaks in the final mass spectrum. As chirality effects can be ruled out for these peaks, varying intensities for LCPL and RCPL are only due to systematic asymmetries and thus can be accounted for and corrected (Logé & Boesl, ; Boesl et al, ). The combination of the twin peak and reference method pushed the detection limit for CD down to the 1‰ level (Logé & Boesl, ; Boesl et al, ), which made CD‐REMPI‐MS applicable to a wide variety of compounds.…”

Determination of accurate electron chiral asymmetries in fenchone and camphor in the VUV range: sensitivity to isomerism and enantiomeric purity

“…Note that fenchone has also been used to demonstrate a pioneering chiroptical method based upon High Harmonic Generation (HHG) from a chiral molecule 38 , and both isomers have been studied by REMPI--UV Ion Yield CD 39 . To be validated in sensitivity and reliability laser--based PECD experiments need benchmarking with data obtained with more well--established and controlled experiments such as the one that can be carried out with pure--CPL SR sources.…”

Analysis of Chirality by Femtosecond Laser Ionization Mass Spectrometry

“…The second important property pertains to the ionization characteristics. 7,17,18 Clearly, the observations described above cannot be rationalized by resonance absorption in the neutral PO. We have further investigated the variation of the ion yields, Y, with the laser pulse energy E, keeping all other laser pulse properties constant.…”

“…[4][5][6][7][8][9][10] All these ns laser ionization techniques employed resonance enhanced multiphoton ionization (REMPI) and the CD observed in each case was dominated by the resonant electronic absorption of the first photon. [4][5][6][7][8][9][10] All these ns laser ionization techniques employed resonance enhanced multiphoton ionization (REMPI) and the CD observed in each case was dominated by the resonant electronic absorption of the first photon.…”