Fast determination of inorganic cations and low mass amines in freshly prepared and moldy green tea samples using IC-MS

Importance of the topic

Reliable analytical methods are essential to ensure food safety, compliance with labeling requirements, and early detection of spoilage in complex matrices such as tea. Fast, selective, and sensitive detection of inorganic cations and low-mass amines supports quality control, contamination screening, and investigation of microbial spoilage in beverages.

Objectives and study overview

This study demonstrates a rapid ion chromatography–mass spectrometry (IC-MS) workflow to separate and detect four common inorganic cations (sodium, potassium, magnesium, calcium) and four amines (monoethanolamine, ethylamine, diethylamine, and related compounds) in freshly brewed and moldy green tea. Analysis time was under six minutes, with simultaneous conductivity and single quadrupole MS detection in full-scan and selected ion monitoring (SIM) modes.

Methodology and workflow

The method employs an RFIC system with eluent generation and suppressed conductivity detection coupled to a single quadrupole mass spectrometer using heated electrospray ionization (HESI). Key parameters:

• Columns: Dionex IonPac CG12A-5 µm and CS12A-5 µm, 3 mm i.d.
• Eluent: 33 mM methanesulfonic acid generated in-line (EGC 500 MSA cartridge) with high-pressure degassing.
• Flow rate: 0.5 mL/min; injection volume: 100 µL; column temperature: 30 °C.
• Conductivity detection: Dionex CERS 500e suppressor, external water mode at 0.7 mL/min.
• MS detection: ISQ EC single quadrupole, +ESI at 3000 V, full scan 18–250 m/z and SIM for target ions without desolvation solvents.

Used Instrumentation

• Thermo Scientific Dionex Integrion HPIC system with RFIC and conductivity detector
• Thermo Scientific Dionex AS-AP autosampler
• Thermo Scientific AXP-MS auxiliary pump
• IonPac CG12A-5 µm and CS12A-5 µm columns
• Dionex EGC 500 MSA cartridge and CR-CTC 600 trap column
• Dionex CERS 500e suppressor
• Thermo Scientific ISQ EC single quadrupole mass spectrometer with HESI II probe
• Thermo Scientific Chromeleon CDS software v7.2 SR6

Main results and discussion

Both freshly brewed and three-day-old moldy tea samples showed clear separation of cations and amines within six minutes. SIM detection delivered high signal-to-noise (E2–E5 counts), while MS improved resolution between closely eluting amines (notably monoethanolamine and ethylamine), which were unresolved by conductivity alone. The moldy sample exhibited increased amine levels, enabling rapid identification of spoilage. Conductivity signals varied minimally between samples, but key amine peaks approached detection limits, highlighting the need for MS confirmation.

Benefits and practical applications

• Rapid screening of tea and similar beverages for cation profiles and spoilage indicators.
• Enhanced selectivity and sensitivity through combined suppressed conductivity and MS detection, enabling confident identification of low-level amines.
• Minimal sample preparation: simple dilution and injection.
• No additional desolvation reagents needed, simplifying operation and reducing maintenance.

Future trends and potential applications

Advances in IC-MS technology will further reduce analysis time and expand target analyte lists, including organic acids and other biogenic amines. Automation and smart data processing will enable real-time monitoring of spoilage markers in production lines. Coupling high-resolution MS and multidimensional chromatography can enhance structural elucidation of novel contaminants in complex matrices.

Conclusion

This application brief showcases a fast, robust IC-MS method for simultaneous determination of inorganic cations and low-mass amines in tea samples. The dual detection mode delivers high sensitivity, selectivity, and resolution, facilitating quality control and spoilage assessment in food and beverage analysis.

References

1. Wang J., Schnute W.C. Optimizing mass spectrometric detection for ion chromatographic analysis. I. Common anions and selected organic acids. Rapid Commun. Mass Spectrom. 2009;23(21):3439–3447. doi:10.1002/rcm.4263
2. Thermo Scientific White Paper 70424: Specific and Selective Detection for Food and Beverage Analysis by Ion Chromatography–Mass Spectrometric Detection, 2016.
3. Thermo Scientific Application Note 269: Identification and Quantification at ppb Levels of Common Cations and Amines by IC-MS.
4. Thermo Scientific AppsLab Library of Analytical Applications.