Dissertation/Thesis Abstract

Ionization Efficiency for Environmentally Relevant Compounds Using Atmospheric Pressure Photoionization Versus Electrospray Ionization
by Shrestha, Prakriya, M.S., Southern Illinois University at Edwardsville, 2019, 146; 13864489
Abstract (Summary)

Despite the advent of modern ionization techniques, many papers continue to report the results of the detection of “ionizable” analytes using an electrospray ionization. This project aims to evaluate the efficacy of two different ionization sources, electrospray ionization (ESI) and atmospheric pressure photoionization (APPI). Each ionization source was coupled with the same high performance liquid chromatography coupled mass spectrometry (HPLC-MS) for quantitation of pharmaceutical compounds. Sample analysis was performed with an Agilent Technologies 6460 Triple Quad UHP LC/MS-MS. This study aims to optimize the mass spectrometry parameters for ESI and APPI using different classes of pharmaceuticals and then compare the final methods’ figures of merit. Since matrix effects interfere with the detection of low-level pharmaceuticals in wastewater, artificial wastewater was used to determine the matrix effect. Wastewater was chosen because of the extensive use of pharmaceuticals that led to an increased disposal of unused drugs and non-metabolized compounds into the environment. Some of the most commonly detected pharmaceuticals include antibiotics and endocrine disruptor compounds (EDCs). EDCs have deleterious effects on non-target organisms including changes in their anatomy, physiology, and reproductive tendencies even at trace levels. As low concentrations of antibiotics are released into the environment, they can lead to antibiotic resistance. Consequently, the detection of low concentrations of pharmaceuticals from environmental samples has drawn attention from those who perform analytical method development. The methods developed here will help to detect the low concentration of pharmaceuticals present in water by minimizing the matrix interference. This work will enable effective choices of the ionization technique for mass spectrometry applications for quantifying antibiotics and EDCs at increasingly lower limits of detection.

Although most of the analytes under study were efficiently ionized by ESI, some of the compounds were better analyzed by APPI. It was found that analytes with a pKa greater than the pH of the mobile phase were generally easily protonated and analyzed efficiently using ESI as the ionization source. Compounds that have a high degree of conjugation usually possess lower ionization energy, facilitating ionization through absorption of a photon, and were therefore detected with higher sensitivity using atmospheric pressure photoionization.

In addition, statistical analysis by comparing the data from calibration curves produced with and without the matrix showed no significant differences. However, the matrix effect was observed at higher concentrations of analytes.

Indexing (document details)
Advisor: Tucker, Kevin
Commitee: Lu, Yun, Voss, Eric J.
School: Southern Illinois University at Edwardsville
Department: Chemistry
School Location: United States -- Illinois
Source: MAI 58/06M(E), Masters Abstracts International
Subjects: Chemistry
Keywords: APPI, Antibiotics, EDCs, ESI, LC-MS
Publication Number: 13864489
ISBN: 978-1-392-24631-3
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