Accurate Mass Analysis of Hydraulic Fracturing Waters

Significance of the Topic

The analysis of hydraulic fracturing waters is critical for environmental monitoring and wastewater management. Polypropylene glycol surfactants (PPGs), used as clay stabilizers and scale inhibitors in fracking fluids, serve as robust tracers due to their low background levels in natural water sources.

Goals and Study Overview

This application note demonstrates a workflow for detecting and characterizing PPG surfactants in flowback and produced waters. The study aims to separate complex polymer mixtures, accurately identify repeating units, and establish a database for rapid screening across multiple field samples collected in the western United States.

Methodology

• Sample Collection: Produced and flowback water samples were obtained onsite from oil/water/gas separators in Colorado, North Dakota, Oklahoma, and Texas, and stored at 4 °C prior to analysis.
• UHPLC Conditions: Separation performed on an Agilent ZORBAX Eclipse XDB-C8 column (4.6 × 150 mm, 3.5 μm) at 25 °C. Mobile phase A: 0.1 % formic acid in water; B: acetonitrile; gradient from 10 % B to 100 % B over 25 min; flow rate 0.6 mL/min; run time 30 min.
• Mass Spectrometry: Agilent 6545 Q-TOF MS with ESI positive mode. Drying gas: 10 L/min at 325 °C; sheath gas: 11 L/min at 350 °C; capillary voltage: 4000 V; mass range m/z 50–1000; resolving power ~30 000 at m/z 1522.

Used Instrumentation

• Agilent 1290 Infinity II LC
• Agilent 6545 Q-TOF LC/MS with Jet Stream technology
• Agilent MassHunter software and Personal Compound Database Library

Main Results and Discussion

The total ion chromatogram revealed two distinct polymer regions: a PEG window (retention 9–12.5 min) with 44 Da mass spacing and a broader PPG region (12.5–19 min) with 58 Da spacing due to multiple isomers. Application of the Kendrick mass defect technique (scaling factor 0.9992787 for 58.0419 Da units) aligned PPG homologues (PPG-PO4 to PPG-PO9) with identical mass defects (~0.029–0.030). MS/MS fragmentation of PPG-PO7 confirmed successive losses of 58.0419 Da and a terminal OH group.
The isomeric complexity broadened peak widths, underscoring the need for accurate mass and retention time databases. A custom PPG PCDL enabled automated screening of ~20 field samples, streamlining compound identification.

Benefits and Practical Applications

• Reliable Tracers: PPGs are scarcely present in background waters, making them specific markers of fracturing activities.
• High Selectivity: Accurate mass and Kendrick filtering differentiate polymer homologues and adducts.
• Rapid Screening: Personal Compound Database accelerates analysis across multiple sites.

Future Trends and Potential Applications

Integration of high-resolution MS with machine learning algorithms may further enhance polymer identification. Expanded databases could include diverse surfactant classes, while real-time field-deployable systems may enable on-site monitoring of wastewater composition.

Conclusion

UHPLC-Q-TOF MS combined with the Kendrick mass defect offers a robust platform for characterizing PPG surfactants in hydraulic fracturing waters. The approach provides accurate polymer assignment, efficient database-driven screening, and reliable environmental tracers.

References

1. Thurman EM, et al. Analytical Chemistry 2014, 86, 9653–9661.
2. Thurman EM, et al. Journal of Hazardous Materials 2017, 323, 11–17.
3. Kendrick E. Analytical Chemistry 1963, 35, 2146–2154.