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Analyzing Photodegraded Styrofoam by Using Py/GC/MS with a Combination EI/PI Ion Source

Product: JMS-Q1500GC GC/MS System

Introduction

Electron ionization (EI) is the most commonly used ionization technique in gas chromatography–mass spectrometry (GC-MS). This hard ionization technique (70eV) provides excessive energy to organic compounds that results in highly reproducible fragment ions with relatively high ion intensities. As a result, EI databases have been created that help with identifying the compounds of interest. Despite this ability to do database searches, some compounds (alkanes, alcohols, etc.) do not produce abundant molecular ions, thus making it difficult to differentiate similar compounds from each other.

By contrast, photoionization (PI) is a soft ionization technique that uses a vacuum ultraviolet (VUV) light source to provide ionization energies in the range of 8–10eV. This range is optimal for the soft ionization of common organic compounds which have an ionization energy in the range of 8–11eV. This low ionization energy results in stronger molecular ion signals and less fragmentation than for EI. Combining an EI library search with PI molecular ion information can improve the accuracy of the qualitative analysis results.

In this work, we report on the qualitative analysis of styrene foam (Styrofoam) before and after photodegradation, using pyrolysis (Py)-GC/MS with an EI/PI combination ion source.

Experiment

Commercial Styrofoam was photodegraded for 10 days using an irradiated UV lamp for O3 sterilization (wavelength: 253.7 nm; output: 1.6 W; Toshiba Corporation). The Styrofoam was set approximately 10cm away from the lamp. After UV irradiation, the discolored surface of the Styrofoam was scraped off and measured as a sample.

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