Evaluation of cationic quaternary amines by ion chromatography and mass spectroscopy (IC-MS)

Importance of the Topic

The safety of the food supply is threatened by residual polar pesticides, including cationic quaternary amines, which pose analytical challenges due to their similar chemistries and mass fragments. Accurate and reliable detection of these compounds is essential for regulatory compliance and public health monitoring.

Objectives and Overview

This study evaluates the performance of the Thermo Scientific Dionex IonPac CS21-Fast-4µm cation-exchange column coupled to an IC-MS system for the analysis of fifteen cationic quaternary amines. The goals are to optimize eluent generation, suppressed conductivity detection and single-quadrupole mass spectrometry (SIM mode), and to demonstrate chromatographic resolution and detection suitability for common polar pesticides and related quaternary amines.

Methodology and Instrumentation

The IC system comprises a Thermo Scientific Dionex ICS-6000 HPIC with Reagent-Free IC dual-pump configuration, EGC 500 methanesulfonic acid (MSA) cartridge, CR-CTC III trap column, CDRS 600 suppressor, and Viper PEEK fittings. A Dionex IonPac CG21-Fast-4µm guard column (2×30 mm) and CS21-Fast-4µm analytical column (2×150 mm) operate at 40 °C with a gradient of 1–40 mM MSA at 0.30 mL/min. The autosampler (AS-AP) delivers 10 µL injections. Suppressed conductivity detection runs at 47 mA with external water regenerant. MS detection uses a Thermo Scientific ISQ EC single quadrupole with HESI-II probe in positive SIM mode (CID 10 V, m/z windows per analyte).

Main Results and Discussion

• Chlormequat, mepiquat, paraquat, diquat, diethanolamine, triethanolamine and trimethylsulfonium exhibited strong, well-resolved peaks by both suppressed conductivity and SIM detection.
• Dimethylhydrazine showed strong conductivity response but weak MS signal; quantitation by conductivity with MS confirmation is recommended.
• Nereistoxin, melamine and cyromazine yielded negligible conductivity signals but produced robust SIM responses at elevated concentrations, requiring MS-based quantitation.
• Propamocarb was retained for over 80 min under the MSA gradient, rendering the method impractical for routine analysis.
• Difenzoquat and 1,2,4-triazole were not detected by either detection mode under the evaluated conditions.

Benefits and Practical Applications of the Method

The combination of the CS21-Fast-4µm column and IC-MS dual detection provides high chromatographic resolution and selective confirmation of cationic amines in complex food matrices. This workflow reduces reliance on high-resolution MS for isobaric species, streamlines QA/QC processes, and supports routine regulatory monitoring of polar pesticides.

Future Trends and Opportunities

• Extension of the method to additional quaternary amine pesticides and their metabolites.
• Integration with high-resolution mass spectrometry for enhanced selectivity in complex samples.
• Automation and high-throughput adaptation for large-scale screening laboratories.
• Development of triple quadrupole IC-MS/MS protocols to improve sensitivity and quantitation limits.

Conclusion

The Thermo Scientific Dionex IonPac CS21-Fast-4µm column coupled to an IC-MS system effectively separates and detects most cationic quaternary amines in a single 20-min run. Out of 15 analytes, 12 were successfully analyzed with defined detection strategies, demonstrating the method’s suitability for food safety and environmental laboratories.

References

1. Fussell RJ, Beck J, Schoutsen F, Bruggink C. Development and validation of IC-MS/MS for polar ionic pesticides in food. J Agric Food Chem. 2017;65:7294–7304.
2. Christison T, Madden JE, Rohrer J. Determination of cationic polar pesticides in oat cereals by IC-ESI-MS. Thermo Scientific Application Note AN001166; 2022.
3. Madden JE. Cationic polar pesticides in food by IC-MS/MS. National Environmental Monitoring Conference; 2021.
4. Adams S, Dickinson M, Fussell RJ. Analysis of polar pesticides by IC-MS/MS. North American Chemical Residue Workshop; 2016.