Comparison of ESI, Unispray, and APCI in LC-MS/MS Analysis of Sarin Metabolite Isopropyl Methylphosphonic Acid

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http://urn.fi/URN:NBN:fi:hulib-201909093461
Title: Comparison of ESI, Unispray, and APCI in LC-MS/MS Analysis of Sarin Metabolite Isopropyl Methylphosphonic Acid
Author: Pusfitasari, Eka Dian
Contributor: University of Helsinki, Faculty of Science
Publisher: Helsingin yliopisto
Date: 2019
URI: http://urn.fi/URN:NBN:fi:hulib-201909093461
http://hdl.handle.net/10138/305339
Thesis level: master's thesis
Abstract: Urine can be used to determine human exposure to nerve agents through the analysis of specific biomarkers. Isopropyl methylphosphonic acid (IMPA) is an important marker of sarin nerve agent, a highly toxic chemical regulated under the Chemical Weapons Convention (CWC). A methodology for sensitive, reliable, and selective determination of IMPA in urine matrix was developed and validated, using liquid chromatography-tandem mass spectrometry (LC-MS/MS). The sample preparation method employs normal phase–solid phase extraction (NP-SPE) using silica based cartridge. Before conducting IMPA analysis, the instrument performance was controlled using a quality control sample. Three different ion sources, namely electrospray ionization (ESI), Unispray, and atmospheric pressure chemical ionization (APCI), were compared in order to define the best method for trace analysis of targeted IMPA. Parameters affecting the ionization process such as cone voltage, capillary voltage, impactor pin voltage, corona voltage, and mobile phase flow rate were optimized. Negative ion mode was selected as the best method for IMPA identification in all three ion sources, and multiple reactions monitoring (MRM) was employed to improve sensitivity and selectivity. The APCI source was shown to be the least sensitive and least efficient ionization technique for IMPA identification. In contrast, using ESI and Unispray resulted in satisfactory data with excellent limit of detection (LOD), limit of quantification (LOQ), precision, and accuracy. The two latter ion sources share the same values of those parameters, i.e. 0.44 ng/mL, 1.46 ng/mL, < 4% precision bias, < 5% accuracy bias, for ESI; and 0.42 ng/mL, 1.38 ng/mL, < 4% precision bias, < 4% accuracy bias, for Unispray. Nonetheless, the Unispray shows better performance in comparison to ESI in producing higher signal intensity/peak area and has lower matrix effect.
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