PŘEDPOVĚDI RETENČNÍCH INDEXŮ V PLYNOVÉ CHROMATOGRAFII BOJOVÝCH CHEMICKÝCH LÁTEK

Significance of the topic

Gas chromatography retention indexes provide a key confirmatory parameter for identifying chemical warfare agents (CWAs) when mass spectrometry alone is inconclusive or reference standards are unavailable. Predictive models based on calculated boiling points can bridge gaps in experimental data and support verification efforts under the Chemical Weapons Convention.

Objectives and study overview

This study aimed to develop a generalized approach to predict retention indexes of alkylphosphonate-based CWAs and related compounds. By introducing “false boiling points” (FBPs) derived from structurally similar reference substances, the method enables estimation of chromatographic behavior in nonpolar stationary phases without direct synthesis of each target analyte.

Methodology and used instrumentation

The approach relies on linear correlations between FBPs and retention indexes across homologous series of alkylphosphonates and silyl esters. Two variants of the Kovats formula were employed: one using direct retention times and a linear temperature program from 40 °C to 280 °C at 10 °C/min on an HP-5MS capillary column. False boiling points were iteratively calculated by additive increments from literature or by back-calculation from measured retention indexes.

Main results and discussion

Correlations for three compound classes (dialkyl esters, monosilyl esters, disilyl esters) yielded regression slopes near 4.6–4.8 and R2 > 0.98. A unified model combining all three classes produced a slope of 4.79 and R2 = 0.988. Comparing calculated versus experimental retention indexes across 500+ data points confirmed regression slopes ~1.0 and minimal intercepts, indicating predictive accuracy within ±20 index units. Back-calculated FBPs for linear and branched alcohol series agreed with literature values within 1–2 °C for unbranched and within 5–10 °C for highly branched analogues. Refinement by excluding outliers related to data transcription errors, vacuum boiling-point corrections, column degradation, or strong steric effects further improved precision.

Benefits and practical applications

• Enables rapid retention-index estimation for CWAs lacking authentic standards.
• Supports structural confirmation of isomeric organophosphorus compounds when mass spectra are ambiguous.
• Can be extended to other compound classes ideal for forensic, environmental, or QA/QC laboratories.

Future trends and possibilities

Integration with advanced quantum-chemical descriptors or machine-learning algorithms could further enhance predictive power. Expanding databases with standardized retention-index measurements and FBPs for diverse functional groups will broaden applicability to novel or emerging threats. Coupling the model with portable GC platforms may facilitate on-site screening in verification missions.

Conclusion

The false-boiling-point approach provides a robust, high-accuracy method for predicting gas chromatographic retention indexes of chemical warfare agents and related organophosphorus chemicals. Its simplicity, reliance on readily available reference data, and strong correlation metrics make it a practical tool for laboratories involved in chemical-weapons verification and analytical method development.

References

• Uchiytil B. Retention Indexes Prediction of Chemical Warfare Compound in Gas Chromatography. Science for Population Protection. 2018;1.
• Kovats E. Gas-chromatographic characterization of organic compounds. Helv Chim Acta. 1958;41:1915–1932.
• Wehrli A, Kovats E. Calculation of retention indexes of aliphatic, alicyclic and aromatic compounds. Helv Chim Acta. 1959;42:2709–2736.
• Ettre LS. Editorial on retention index methodology. Anal Chem. 1964;36(8):31A.
• Schomburg G. Gas-chromatographic retention data and structure of compounds. J Chromatogr. 1964;14:157–177.
• Purnell H. Gas chromatography. Prague: SNTL; 1966.
• Pacáková V, Feltl L. Retention indexes in gas chromatography. Prague; 1986.
• Söderström MT, Ketola RA, Kostiainen O. Identification of nerve agent homologues by GC-FTIR. Fresenius J Anal Chem. 1995;352:550–556.
• Kosolapoff GM. Organophosphorus Compounds. J Wiley & Sons; 1950.
• Czech Ministry of Industry and Trade Decree No. 208/2008.