Specific determination of non-ionic surfactants in drinking-, waste- and surface water with high resolution mass spectrometry

Significance of the Topic

Nonionic surfactants such as alkylphenol polyethoxylates (APEO) and alcohol ethoxylates (AEO) are extensively employed in household and industrial cleaning agents. Their degradation products are more toxic and persistent, posing environmental and health concerns. Effective monitoring of these compounds in water matrices is essential for risk assessment, regulatory compliance, and safeguarding ecosystem health.

Study Objectives and Overview

This study aims to develop a robust, simultaneous screening method for nonionic surfactants in drinking, surface, and wastewater. Key objectives include systematic identification, semi-quantification of a broad range of ethoxylate chain lengths, and implementation of a cost-effective, time-saving workflow using high-resolution LC-MS/MS.

Methodology and Instrumentation

Sample preparation involves spiking 10 mL of water with 10 mL acetonitrile, filtration through a 0.45 µm membrane, and injection of 5 µL onto a C18 UHPLC column (150 mm×2.1 mm, 1.7 µm) at 50 °C. Gradient elution uses 5 mM ammonium acetate in water (A) and acetonitrile (B), with a flow rate of 0.4 mL/min. MS detection employs a Shimadzu LCMS-9050 Q-TOF, positive electrospray ionization (4.5 kV), scan range 100–1000 Da at 10 Hz, interface temperature 350 °C, DL temperature 250 °C, and heat block at 400 °C. Data analysis extracts chromatograms of mass differences of 44 Da, corresponding to ethoxylate units, summing XIC areas. Calibration uses APEO C9 and AEO C12 standards (31.8–1000 µg/L) with quadratic regression and 1/C² weighting.

Results and Discussion

Calibration curves for APEO C9 and AEO C12 exhibited excellent linearity (r² > 0.999) over the tested range. The method successfully detected and semi-quantified short-chain ethoxylates in real drinking, surface, and wastewater samples. Total ion chromatograms revealed distinct homolog series, and targeted mass spectra confirmed chain lengths and isotopic patterns. APEO C6 was quantified at 1.08 ppb in a surface water sample, demonstrating the method’s sensitivity.

Benefits and Practical Applications

• Semi-automated workflow accelerates data processing and reduces manual interpretation.
• Comprehensive coverage of nonionic surfactant homologues improves screening capabilities.
• Cost-effective approach suitable for routine environmental monitoring.
• High resolution and accurate mass enhance selectivity and confidence in identification.

Future Trends and Opportunities

• Extension to cationic and anionic surfactant classes.
• Incorporation of isotopically labeled standards for absolute quantification.
• Integration of machine learning for automated spectral annotation.
• Development of portable or in situ LC-MS platforms for on-site monitoring.
• Coupling chemical data with bioassays to link concentrations with biological effects.

Conclusion

The developed high-resolution LC-MS/MS method enables efficient, simultaneous analysis of a wide range of nonionic surfactants in various water matrices. Its high sensitivity, accuracy, and semi-automated data processing support reliable environmental monitoring and risk assessment.