Simultaneous analysis of alkylphenol ethoxylates using ultra-high speed LC-MS/MS

Importance of the topic

Alkylphenol ethoxylates (APEs) such as nonylphenol ethoxylates (NPEs) and octylphenol ethoxylates (OPEs) are widely used non-ionic surfactants in textile manufacturing and various industrial processes. Their environmental persistence and biodegradation to alkylphenols pose risks to aquatic ecosystems and human health. Reliable methods are therefore needed for rapid, sensitive detection and quantification of APEs in industrial and environmental samples.

Study objectives and overview

This work aimed to develop a simultaneous screening and quantitation method for APEs using ultra-high speed liquid chromatography coupled with tandem mass spectrometry (UHPLC-MS/MS). The approach combines multiple precursor ion scans for broad screening with multiple reaction monitoring (MRM) for targeted quantitation in a single 15-minute run.

Methodology and instrumentation

Standards of NPEs (C9 alkyl chain) and OPEs (C8 alkyl chain) with varying ethoxylate (EO) lengths (3–18 EO units for NPEs, 2–16 EO for OPEs) were diluted in methanol. A textile product extract was also analyzed to demonstrate real-sample performance.

• UHPLC: Shimadzu Nexera X2 with Zorbax Eclipse XDB-C18 or Cadenza CD-C18 column (150×2.1 mm or 150×2 mm; 5 µm or 3 µm); 40 °C; flow rate 0.3 mL/min; injection 5 µL.
• Mobile phase: gradient from 60% to 98% acetonitrile in 10 mM ammonium acetate buffer over 10 min, then re-equilibration to 60%.
• MS/MS: Shimadzu LCMS-8030 triple quadrupole with ESI positive ionization (+4.5 kV), ultra-fast polarity switching (15 ms), and up to 555 MRM transitions/s.

Main results and discussion

All APE homologues produced protonated molecular ions [M+H]+ and yielded a common fragment ion at m/z 89. Collision energies ranged from 31 V (shorter EO chains) to 56 V (longer EO chains). Chromatographic separation eluted OPEs first (16 → 3 EO) followed by NPEs (18 → 3 EO) within a 15 min program, achieving baseline resolution for most homologues.
The calibration curves for all standards showed excellent linearity (R2 > 0.99) and low detection limits. Real textile sample analysis confirmed the presence of multiple APEs, demonstrating method applicability to complex matrices.
For non-targeted screening, four fast precursor ion scans (m/z 200–1200) at collision energies 20, 30, 40, and 50 V were performed in a single 1 s loop, enabling rapid profiling of APE chain lengths without mass shifts thanks to the high-speed MS/MS capability.

Benefits and practical applications

This combined screening-quantitation workflow offers:

• High throughput analysis of APEs in under 15 min per sample.
• Sensitive and selective quantitation using MRM with a single diagnostic fragment (m/z 89).
• Rapid screening of unknown APE homologues by precursor ion scanning in a single run.
• Applicability to quality control in textile manufacturing, environmental monitoring of effluents, and regulatory compliance testing.

Future trends and applications

Future developments may include coupling this method with high-resolution mass spectrometry to identify unknown degradation products and isomers. Automation of sample preparation and data processing will further increase throughput. Integration with environmental risk assessment workflows could streamline monitoring of APEs in water and soil.

Conclusion

An ultra-high speed UHPLC-MS/MS method has been established for simultaneous screening and quantitation of alkylphenol ethoxylates. The approach delivers rapid, sensitive, and selective analysis of APE homologues in both standards and real samples, supporting environmental surveillance and industrial quality control.