Accurate Mass Analysis of Hydraulic Fracturing Waters: Identification of Polyethylene Glycol Surfactants by LC/Q-TOF-MS

Significance of the Topic

Identification of ethoxylated surfactants such as polyethylene glycols (PEGs) in hydraulic fracturing flowback waters is critical for environmental monitoring and contamination tracing.
Potential leakage of fracking fluids can impact groundwater and surface water quality, driving the need for robust analytical markers.

Objectives and Study Overview

The study aimed to develop a rapid ultra-high-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UHPLC/Q-TOF-MS) workflow to detect and characterize PEG surfactants in flowback samples.
It applied the Kendrick mass defect approach to distinguish PEG oligomers and created an accurate-mass database for fast screening.

Methodology and Instrumentation

The method employed an Agilent ZORBAX Eclipse XDB-C8 column with a water/formic acid and acetonitrile gradient at 0.6 mL/min.
Mass detection used positive electrospray ionization and high-resolution Q-TOF-MS with internal mass calibration for 30 000 resolving power.

Used Instrumentation

• Agilent 1290 Infinity LC System
• Agilent 6540 Ultra High Definition Accurate-Mass Q-TOF LC/MS with Jet Stream ESI

Main Results and Discussion

Chromatograms revealed a bimodal PEG distribution: a hydrophilic zone (4–12 min) and a less-polar zone (12–14 min), with repeating 44.026 Da mass units corresponding to CH2-CH2-O.
Kendrick mass scaling identified consistent mass defects across PEG oligomers (PEG-3 to PEG-11) and their proton, sodium, and ammonium adducts.
MS/MS fragmentation confirmed linear PEG structures through successive losses of 44 Da.
A shift from sodium to ammonium adduct dominance at higher oligomers was observed, attributed to cage-like stabilization of NH4+.

Benefits and Practical Applications

The accurate-mass database of over 40 PEG species enables rapid (<2 min) screening of water samples for PEG tracers.
This approach supports environmental monitoring, quality control, and regulatory compliance in fracking operations.

Future Trends and Potential Uses

Expansion to other ethoxylated surfactants and real-time field monitoring platforms is anticipated.
Integration with automated MS/MS libraries and environmental data analytics can enhance contaminant tracking.

Conclusion

The developed UHPLC/Q-TOF-MS method, combined with Kendrick mass defect analysis, provides a fast and reliable means to detect and characterize PEG surfactants in hydraulic fracturing waters, offering valuable tools for environmental assessment.

References

1. Kargbo DM, Wilhelm RG, Campbell DJ. Natural gas plays in the Marcellus Shale: Challenges and potential opportunities. Environ Sci Technol. 2010;44:5679–5684.
2. Thurman EM, Ferrer I, Blotevogel J, Borch T. Analysis of hydraulic fracturing flowback and produced waters using accurate mass: identification of ethoxylated surfactants. Anal Chem. 2014;86:9653–9661.
3. Kendrick E. A mass scale based on CH2=14.0000 for high resolution mass spectrometry of organic compounds. Anal Chem. 1963;35:2146–2154.