A High Sensitivity Method for Quantitative Determination of Ten Phenols in Surface Water on LC/MS/MS with APCI Interface

Significance of the Topic

The presence of phenolic compounds in surface waters is a critical concern due to their toxicity, potential carcinogenicity, and widespread use in industrial, agricultural, medical, and domestic applications. Regulatory agencies such as the US EPA and the European Community impose strict limits (0.1 µg/L for individual phenols) to safeguard drinking water and environmental quality. Accurate, sensitive, and efficient analytical methods are therefore essential for monitoring and compliance.

Objectives and Overview of the Study

This study focused on developing a fast, high‐sensitivity LC-MS/MS method with an APCI interface for simultaneous quantitation of ten phenolic compounds in treated and reservoir water samples. The target analytes comprised unsubstituted phenol and nine substituted phenols, including alkylphenols, chlorophenols, and nitrophenols. The method aimed to eliminate extensive sample preparation by employing direct injection and a rapid gradient elution.

Methodology

An optimized multiple reaction monitoring (MRM) approach was established using a Shimadzu LCMS-8050 triple quadrupole mass spectrometer coupled with a Nexera UHPLC system. Separation was achieved on a pentafluorophenyl (PFP) column (100 mm × 2.1 mm, 2.6 µm) with a binary mobile phase of water and methanol under an 8-minute gradient. Two MRM transitions per compound were selected for quantification and confirmation. Calibration curves were constructed over 0.05–10 µg/L for most analytes (R2 > 0.995) and up to 10 µg/L for phenol and 2,4-dimethylphenol.

Applied Instrumentation

• UHPLC System: Shimadzu Nexera.
• Mass Spectrometer: Shimadzu LCMS-8050 triple quadrupole.
• Ionization Interface: Atmospheric pressure chemical ionization (APCI) in negative mode.
• Column: Phenomenex Kinetex PFP, 100 mm × 2.1 mm, 2.6 µm.
• Mobile Phase: A = water, B = methanol; gradient from 5% to 95% B.
• Flow Rate: 0.5 mL/min; column oven at 40 °C; injection volume 10 µL.
• Gas Conditions: Nebulizing gas N2 at 4 L/min; drying gas N2 at 5 L/min; interface temperature 500 °C.

Main Results and Discussion

The method achieved baseline separation of all ten phenols, including isomeric nitrophenols (2-NP, 4-NP at 3.40 and 3.51 min). Calibration exhibited excellent linearity (R2 > 0.995) across the tested range. Limits of detection were between 0.02 and 0.25 µg/L for eight substituted phenols; phenol and 2,4-dimethylphenol showed higher LODs at 1.0 µg/L due to lower APCI ionization efficiency. Direct injection of control water samples (low and high spiked levels) confirmed accurate quantitation of all analytes except phenol and 2,4-dimethylphenol at low levels. Analysis of treated and reservoir water detected only 2-NP and 4-NP at concentrations below regulatory thresholds.

Benefits and Practical Applications

• Direct injection without sample pre-concentration or derivatization reduces analysis time and labor.
• Fast 8-minute gradient enables high sample throughput.
• Sufficient sensitivity for eight substituted phenols meets drinking water regulations.
• MRM transitions provide reliable confirmation and quantitation for environmental monitoring.

Future Trends and Possibilities

Enhancements in ionization techniques, such as dopant-assisted APCI or alternative interfaces, could improve sensitivity for low-polarity phenols. Integration of on-line enrichment (for example, SPE or SPME) and automation may extend applicability to ultra-trace levels and complex matrices. Expansion of MRM libraries and application of chemometric data analysis and artificial intelligence could further streamline routine water quality screening and real-time monitoring.

Conclusion

A rapid MRM-based LC-APCI-MS/MS method was established for ten phenols, achieving regulatory detection limits for eight substituted compounds without pre-concentration. Phenol and 2,4-dimethylphenol require additional sample enrichment to reach sub-µg/L sensitivity. The approach offers a streamlined workflow for environmental laboratories to monitor priority phenolic pollutants in surface and drinking water.

Reference

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6. Shimadzu Application News No. C96.