Analysis of linear alkylbenzene sulfonate in environmental water using online SPE LC system coupled with LC-MS/MS

Importance of the Topic

Linear alkylbenzene sulfonates (LAS) represent the most common anionic surfactants released into aquatic environments through household effluent. Their presence, even at trace levels, poses ecological risks to aquatic organisms. Reliable and efficient monitoring of LAS in environmental waters is therefore critical to support regulatory compliance and environmental protection efforts.

Study Objectives and Overview

The study aimed to develop and validate an automated analytical workflow combining online solid-phase extraction (SPE) with liquid chromatography-tandem mass spectrometry (LC-MS/MS) for sensitive and robust quantification of six LAS homologues (C8, C10–C14) in river water. Key goals included minimizing manual sample preparation, improving detection limits, and achieving accurate recoveries in complex matrices.

Methodology and Instrumentation

A two-column LC-MS/MS system was configured to automate sample clean-up and separation:

• Online SPE column: CHEMCO MASK-ENV (10 mm L. × 2.0 mm I.D.) for preconcentration and matrix removal.
• Analytical column: Shim-pack XR-ODS II (100 mm L. × 2.0 mm I.D., 2.2 µm particle size).
• Mass spectrometer: Shimadzu LCMS-8040 triple quadrupole with ESI source operating in negative polarity and fast polarity switching.
• Mobile phases: A) 50 mM ammonium formate + 0.1% formic acid in water; B) acetonitrile.
• Gradient elution: 65% B (0–20 min), 95% B (20.01–28 min), return to 65% B (28.01–30 min).
• MRM transitions (deprotonated molecular ion → m/z 183): C8 (269→183), C10 (297→183), C11 (311→183), C12 (325→183), C13 (339→183), C14 (353→183).

Sample injection volume was increased to 50 µL for the online SPE workflow. Dilution pumps were incorporated to reduce acetonitrile content during trapping, enhancing retention of LAS on the SPE cartridge.

Main Results and Discussion

The optimized method delivered excellent analytical performance:

• Sensitivity: Limits of detection down to 0.1 ppb for all LAS homologues without interference from river water matrix.
• Linearity: Calibration curves over 0.1–10 µg/L exhibited coefficients of determination (R2) ≥ 0.996.
• Repeatability: Intraday RSD ≤ 1.2% at 0.5 ppb (n = 5).
• Recoveries: Spiked river water (1 ppb) yielded 94.6–102.9% recoveries (n = 3), demonstrating effective matrix removal.

This automated configuration substantially reduced manual handling and solvent consumption compared to offline SPE approaches, while maintaining high throughput and reproducibility.

Benefits and Practical Applications

The combined online SPE LC-MS/MS method offers:

• Automated sample loading, clean-up, and analysis in a single workflow.
• Enhanced sensitivity and precision suitable for trace-level environmental monitoring.
• Rapid turnaround for regulatory laboratories and research settings.
• Reduction of labor and potential sample contamination associated with manual SPE.

These advantages make the method well suited for routine surveillance of surfactant pollution in rivers, wastewater effluents, and other water bodies.

Future Trends and Applications

Advances likely to further enhance surfactant analysis include:

• Integration with high-resolution mass spectrometry for broader non-targeted screening of emerging contaminants.
• Miniaturized and portable SPE-LC-MS/MS systems for on-site monitoring.
• Development of multiplexed workflows to analyze diverse surfactant classes simultaneously.
• Applications in treatment process optimization and environmental fate studies.

Conclusion

An online SPE LC-MS/MS approach was successfully established for automated, sensitive, and reliable determination of LAS in environmental water samples. The method achieved low detection limits, excellent linearity, and high recoveries, demonstrating its suitability for routine environmental monitoring.