# Application of Chemical Ionization in the Analysis of Ethylphosphonic Acid Derivatives

## TL;DR

This paper explores how chemical ionization mass spectrometry can be used to analyze ethylphosphonic acid derivatives, which are relevant to chemical weapons identification.

## Contribution

The study introduces a method for predicting mass spectra and retention parameters of ethylphosphonic acid derivatives using chemical ionization.

## Key findings

- Protonated molecules with high intensities were observed using methane in chemical ionization.
- Retention parameters and mass spectra of five new compounds were successfully determined.
- The method proved effective for identifying substances relevant to chemical weapons analysis.

## Abstract

The
microsynthesis of 32 dialkyl derivatives of ethylphosphonic
acid and the same number of monoalkyl derivatives was carried out
to perform comparative studies using gas chromatography combined with
mass spectrometry in chemical ionization mode which is one of the
analytical techniques recommended by the Organisation for the Prohibition
of Chemical Weapons (OPCW). The huge number of possible representatives
makes it difficult to have complete spectral libraries of all substances
in this class. Therefore, we decided to synthesize and instrumentally
analyze only representatives of the selected series of homologues
in this work. The analysis of the obtained results allowed us to find
the rules for predicting mass spectra and the factors determining
the retention parameters. Symmetrical diesters and monoesters of ethylphosphonic
acid were selected for this study. During the conducted experiments
using chemical ionization with methane as the reaction gas, protonated
analyte molecules with high relative intensities were obtained; in
many cases, these are base peaks in the spectrum. The obtained results
allow grouping of the synthesized compounds depending on the introduced
alkyl substituent. Retention data of the tested analytes were collected
during the research by using electron ionization. The retention parameters
of the tested compounds from each homologous series were also summarized
and compared. Chemical Warfare Agents (CWA) analysis continues to
be an important issue, especially in the context of the regular Proficiency
Tests organized by the OPCW for identifying chemical compounds that
are of interest to the Chemical Weapons Convention. Five compounds
were synthesized whose spectra were not available in EI mass spectral
libraries, and their retention indices were unknown. The identification
of these substances was supported by the CI mass spectra and retention
data, using previously developed relationships. Therefore, it is reasonable
to conclude that the research method used is useful and effective.