Multiphoton ionization and circular dichroism: New experimental approach and application to natural products

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. Setting sights on chiral molecules: The combination of circularly polarized laser light and time-of-flight mass spectrometry (ToF-MS, see picture) allows for enantio-sensitive mass-selective spectroscopy and analysis of chiral molecular systems (CD-REMPI=circular dichroism resonance-enhanced multiphoton ionization).