Using ion chromatography with electrospray ionization mass spectrometry for the determination of cations and amines in alkanolamine scrubbing solutions

Importance of the Topic

Natural gas processing often involves removing acidic gases such as CO2 and H2S using alkanolamine scrubbing solutions. Over time, heat stable amine salts accumulate, leading to corrosion, reduced scrubbing efficiency, and increased maintenance costs. Accurate monitoring of inorganic cations (ammonium, sodium, calcium, magnesium, potassium) and alkanolamine concentrations at trace levels is essential to maintain process efficiency and ensure product purity.

Objectives and Study Overview

This application note presents a method that couples ion chromatography (IC) with electrospray ionization mass spectrometry (ESI-MS) to identify and quantify ammonium (µg/L to mg/L), calcium, and alkylamines in high concentrations of methyldiethanolamine (MDEA), diethanolamine (DEA), and ethanolamine (EA) scrubbing solutions. The aim is to demonstrate the sensitivity, selectivity, and real-world applicability of this approach.

Methodology and Instrumentation

A Thermo Scientific Dionex Integrion HPIC system with Reagent-Free IC (RFIC) was used, configured with a CG19-4µm guard column and a CS19-4µm separation column. An electrolytically generated methanesulfonic acid (MSA) gradient (4–60 mM) was applied at 0.25 mL/min and 30 °C. Suppressed conductivity detection employed a CERS 500e suppressor in external water mode. A Thermo Scientific ISQ EC single quadrupole mass spectrometer with an HESI-II probe introduced the effluent without a make-up solvent. Data acquisition and instrument control were handled by Chromeleon CDS software. Samples were diluted 1000-fold, filtered, and calibrated using serial dilutions of combined cation and individual amine standards. MS conditions (vaporizer temperature, gas flows, CID voltages) were optimized via infusion and IC-MS experiments.

Main Results and Discussion

Chromatographic separation was achieved within 35 minutes, resolving inorganic cations and alkanolamines. Cations were detected as hydrate adducts (NH4+·H2O at m/z 36, Na+·2H2O at m/z 59) using selected ion monitoring (SIM), while alkylamines were monitored in both full scan and SIM modes. Calibration curves exhibited second-order quadratic fits with r² ≥ 0.99. Method detection limits (MDLs) were 8 µg/L for sodium, 4 µg/L for potassium, 22 µg/L for ammonium, 15 µg/L for magnesium, and 64 µg/L for calcium. Spike recoveries ranged from 99% to 104% for cations and 89% to 101% for alkanolamines. Analysis of refinery samples confirmed the method’s applicability, detecting trace cations in high-concentration alkanolamine matrices.

Benefits and Practical Applications

• High sensitivity and selectivity for trace cations in complex matrices
• Combined conductivity and MS detection enhances confirmatory analysis
• No make-up solvent required, reducing complexity and cost
• Applicable for QA/QC monitoring in gas processing and chemical manufacturing

Future Trends and Applications

• Integration with high-resolution MS for structural characterization of degradation products
• Automation and miniaturization for field-deployable analysis systems
• Extension to anion, amino acid, and other ionic species determinations
• Advanced data analytics and real-time process monitoring

Conclusion

The IC-ESI-MS method on the Dionex Integrion HPIC and ISQ EC platform provides a robust, sensitive, and efficient solution for simultaneous monitoring of inorganic cations and alkanolamines in gas scrubbing solutions. It enables reliable quantification at low µg/L levels within high matrix concentrations, supporting improved process control and product quality.

Reference

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