Determination of Alkylphenols and Alkylphenol Mono- and Diethoxylates in Sewage Sludge by High Speed Gas Chromatography/Mass Spectrometry

Significance of the Topic

Nonylphenol (NP) and its ethoxylated metabolites NP1EO and NP2EO are persistent, toxic transformation products of alkylphenol ethoxylate surfactants widely used in industrial and household applications. These compounds accumulate in sewage sludge, pose endocrine disruption risks, and are subject to emerging European regulatory limits, highlighting the need for robust analytical monitoring.

Objectives and Study Overview

• Establish a rapid, routine method to quantitatively determine NP, NP1EO and NP2EO in sewage sludge.
• Compare results with an existing normal-phase HPLC method.
• Demonstrate method applicability across varied sludge matrices.

Methodology and Instrumentation

Sludge samples were lyophilized and fractionated (<200 µm). One gram of sample was spiked with deuterated NP (NP-d8) and extracted using a Soxtec system with hexane/acetone (50/50) at 180 °C for 45 min. The extract was concentrated, purified on a Florisil cartridge, and derivatized at room temperature with Sigma-Sil-A before GC/MS analysis.

Instrumentation

• Foss Soxtec® extraction system
• Zymark Turbovap® nitrogen concentrator
• Agilent 6890 GC with 5973 MSD
• RTX-5 capillary column (20 m×0.10 mm×0.10 µm)
• Agilent 7673 autosampler

Main Results and Discussion

• High-speed GC/MS separated NP, NP1EO, and NP2EO into three distinct isomer groups, improving compound fingerprinting.
• Selected-ion monitoring (SIM) achieved limits of quantification of 2 µg/g DM for NP and 5 µg/g DM for NP1EO and NP2EO.
• Method validation showed excellent linearity (R²>0.9989), repeatability (RSD<7%), accuracy (recoveries >86%), and reproducibility (RSD<20%).
• Analysis of 10 French sewage sludge samples yielded total NP + NP1EO + NP2EO concentrations of 8.8–210 mg/kg DM (median 91 mg/kg DM), frequently exceeding the proposed 50 mg/kg DM regulatory threshold. NP2EO accounted for up to 80% of the total load.

Benefits and Practical Applications of the Method

• Rapid chromatographic runtime (<20 min) and high throughput.
• Enhanced sensitivity and selectivity via derivatization and GC/MS detection.
• Effective cleanup minimizes matrix interferences, ensuring robustness across sludge types.
• Direct applicability for environmental compliance and regulatory monitoring.

Future Trends and Potential Applications

Extensions of this approach may include direct analysis of wastewater, broader profiling of NPEO homologues, adoption of LC/MS or supercritical fluid techniques for labile compounds, and integration of automated sample handling for high-throughput environmental surveillance.

Conclusion

The presented method combining Soxtec extraction, Florisil cleanup, Sigma-Sil-A derivatization, and high-speed GC/MS delivers reliable, sensitive, and rapid quantification of NP and its ethoxylates in sewage sludge, supporting regulatory compliance and routine environmental monitoring.

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