Photoionization/Photoinduced Chemical Ionization Source Based on Radio Frequency Amplitude Modulation on an Ion...

Area of Science:

• Analytical Chemistry
• Mass Spectrometry
• Environmental Science

Background:

• Photoionization (PI) is valuable for analyzing volatile organic compounds (VOCs) due to its sensitivity and non-destructive nature.
• Limitations of traditional PI sources include inefficient ion transmission at high pressures and insufficient photon energy for certain compounds.

Purpose of the Study:

• To develop an improved photoionization source, the ion-funnel-integrated photoionization (IFPI) source, to overcome existing limitations.
• To implement a dual-mode ionization strategy for enhanced VOC detection.

Main Methods:

• Development of an IFPI source integrating an ion funnel with a PI source.
• Systematic investigation of radio frequency (RF) amplitude effects on ion transmission and ionization.
• Implementation of a dual-mode strategy using RF amplitude modulation (low and high modes).
• Optimization of ion source pressure, RF amplitude, and ion funnel DC voltage difference.
• Detection of 11 VOCs using time-of-flight mass spectrometry (TOFMS) coupled with the IFPI source (IFPI-TOFMS).

Main Results:

• The low-amplitude RF mode (40 V) increased single-photon ionization (SPI) sensitivity over 10-fold via ion funnel focusing.
• The high-amplitude RF mode (80 V) enabled detection of compounds with higher ionization energies using O2+ charge transfer from photoelectron ionization (PEI).
• Optimized IFPI-TOFMS achieved limits of detection (LODs) for 11 VOCs between 2.3–32.5 parts per trillion by volume (pptv).

Conclusions:

• The IFPI source effectively enhances VOC analysis sensitivity and broadens the detectable compound range.
• IFPI-TOFMS demonstrates practical utility for environmental health and public safety applications, including long-term air monitoring and spatial distribution analysis.