Simultaneous determination of tetrabutylammonium and tributylamine in wastewater by IC/LC-MS

Importance of the Topic

The widespread use of trialkylamines (TAMs) and quaternary ammonium compounds (QACs) in detergents, disinfectants, and fabric softeners has led to persistent contamination of wastewater and aquatic habitats.
Resistance of QACs to biological degradation and toxicity of cationic surfactants raise ecological concerns, demanding robust methods for trace-level monitoring.

Goals and Study Overview

This work aimed to develop a fast, selective, and sensitive chromatographic workflow for simultaneous determination of tributylamine and its precursor tetrabutylammonium in industrial wastewater.
Key objectives included eliminating derivatization steps, minimizing sample preparation, and achieving low mg/L detection limits with high throughput.

Instrumentation Used

• Thermo Scientific Dionex ICS-6000 system with DP pump and DC detector modules
• Thermo Scientific ISQ EC single quadrupole mass spectrometer with heated electrospray ionization
• Dionex IonPac NS1-5µm analytical column with NG1 guard column
• CERS 500e cation electrolytically regenerated suppressor in external water mode
• PEAK Scientific Genius NM32LA nitrogen generator
• Chromeleon CDS version 7.2

Methodology

Samples were simple 10– to 20-fold dilutions of industrial wastewater with deionized water.
An isocratic ion-pair chromatography method used 2 mM formic acid and acetonitrile (56%) at 1.0 mL/min, directly feeding the effluent into the MS detector.
No derivatization or solid-phase extraction was required.
SIM channels at m/z 186.4 for tributylamine and m/z 242.5 for tetrabutylammonium provided selective detection.

Main Results and Discussion

Chromatograms demonstrated baseline separation and symmetric peaks within a 9-min injection cycle.
Limits of detection were 0.023 mg/L for tributylamine and 0.10 mg/L for tetrabutylammonium, with limits of quantification of 0.075 mg/L and 0.32 mg/L, respectively.
Calibration showed r2>0.999 using second-order polynomial fits.
Intra- and inter-day precision for retention time was ≤0.9% RSD and for peak area ≤2.5% RSD.
Mass spectra confirmed no in-source decomposition of tetrabutylammonium to tributylamine.

Benefits and Practical Applications

• Streamlined workflow with minimal sample preparation reduces analysis time and labor.
• Isocratic conditions and polymeric column avoid matrix interactions and ensure reproducible retention.
• Single-quadrupole MS detection provides high selectivity without the need for internal standards.
• Method can be extended to other low molecular weight TAMs and QACs in environmental monitoring and wastewater quality control.

Future Trends and Potential Applications

Integration of high-resolution MS or tandem MS could further enhance sensitivity and identification of homologous QACs in complex matrices.
Automation of dilution and sample tracking will support high-throughput environmental screening.
Coupling with online solid-phase extraction could lower detection limits and broaden target analyte scope.

Conclusion

A robust IC/LC-MS method was established for direct simultaneous quantification of tributylamine and tetrabutylammonium in industrial wastewater.
The approach combines fast isocratic chromatography, selective MS detection, and simple dilution to deliver low-mg/L detection limits with high precision and throughput.

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