Mass Spectrometry Applications for Environmental Analysis

Significance of the Topic

The increasing public health and environmental concerns over pesticide and herbicide contamination in water demand fast, sensitive, and robust analytical methods. Traditional sample preparation (liquid–liquid extraction, SPE) and long chromatographic runs limit throughput and can lead to analyte loss. Emerging techniques—direct ionization, on-line solid phase extraction (SPE), fast LC separations, and high-resolution mass spectrometry (HRMS)—address these challenges, enabling sub-ppb to fg/L detection in drinking, surface, and environmental waters.

Aims and Overview of the Study

Across multiple application reports, researchers have developed and compared:

• DART® direct analysis coupled to Orbitrap HRMS for rapid screening of 23 common pesticides in water, achieving mass accuracy <1 ppm and 1 ng/mL sensitivity.
• Online SPE with EQuan™ and TSQ Quantum Access™ MAX for automated pre-concentration of herbicides, enabling large-volume (1–20 mL) injections and quantitation at low-pg/mL levels.
• Fast-HPLC separations with divert valve strategies to resolve early-eluting pesticides in acetonitrile extracts and extend injection volumes up to 8–10 μL.
• TraceFinder™ software workflows for targeted and non-targeted LC-MS/MS screening of triazines in drinking water with sub-ppt detection limits.
• EPA Method 549.2 compliance by direct injection and LC-MS/MS quantitation of triazine degradates at 0.25–5 ng/mL.
• On-line SPE with mixed-mode Acclaim™ Trinity P1/Q1 columns and UV detection for paraquat/diquat in water, achieving MDLs ~0.1 µg/L.

Methodology and Instrumentation

• Direct Analysis in Real Time (DART) coupled to Thermo Scientific™ Exactive Orbitrap for atmospheric pressure chemical ionization of pesticides on mesh strips; fast 30-s acquisition at 50,000 resolving power.
• Online SPE systems (EQuan, Dionex UltiMate RSLC x2 DualPump) with guard and analytical columns (Hypersil GOLD, Trinity mixed-mode) for large volume injections, back-flush switching via multi-port valves.
• Fast-HPLC on sub-2 µm UHPLC columns (Hypersil GOLD PFP 100×2.1 mm) for 3-min separations; flow rates up to 850 µL/min.
• Triple quadrupole LC-MS/MS (TSQ Quantum Access MAX) in selected-reaction monitoring (SRM) with polarity switching or single-polarity modes; full-scan product ion spectra via reverse energy ramps (RER) for MS/MS confirmation.
• Chromeleon™ and TraceFinder™ software for unified qualitative screening, library/database searching, automatic calibration, flagging, and reporting.

Main Results and Discussion

• DART-Orbitrap identified all 23 pesticides with mass accuracy 0.05–0.87 ppm; 1 ng/mL ng-level sensitivity demonstrated for acetochlor.
• EQuan SPE-LC-MS: 20 mL direct injections quantified 20 pesticides at 0.02–0.60 µg/L with r² >0.99; 6-min run times on Fast-HPLC.
• Divert valve approach avoided peak splitting for early eluters in acetonitrile extracts; injection volumes up to 8 µL yielded R² >0.99 and RMS S/N >10 at 5 µg/L.
• TraceFinder workflows achieved sub-ppt triazine quantitation (0.1–10 pg/mL) with R² ≥0.992 and no carryover in 20 mL water injections.
• EPA 549.2 direct injection LC-MS/MS separated triazines in 20 min; linearity from 0.25–5 ng/mL with R² ≥0.996;
• Mixed-mode online SPE with UV detection resolved paraquat/diquat in <7 min; method detection limits 0.09–0.10 µg/L, recoveries 104–108% in tap/pond water.

Benefits and Practical Applications

• Dramatic reduction of sample prep and analysis time (minutes instead of hours/days).
• High throughput screening compatible with environmental monitoring, QA/QC, food safety, forensics.
• Minimized solvent usage and operator intervention via on-line SPE and direct ionization.
• Enhanced confidence in identifications through HRAM, MS/MS spectra, and software-driven flagging.

Future Trends and Opportunities

• Integration of automated sample introduction with robotics for unattended operation.
• Expanded HRAM libraries and machine-learning–based non-target screening for emerging contaminants.
• Miniaturization and field-deployable DART-MS and portable LC-MS systems for on-site environmental analysis.
• Coupling ion-mobility separations to further resolve isobaric interferences.

Conclusion

Recent advances in direct ionization, on-line SPE, fast chromatographic separations, and HRMS have enabled rapid, sensitive, and reliable analysis of pesticides and herbicides in water at ppt to sub-ppt levels. These automated, high-throughput workflows meet or exceed regulatory requirements while reducing solvent consumption, labor, and turnaround time.

Reference

1. U.S. EPA Method 549.2, ‘‘Determination of Paraquat and Diquat in Drinking Water,’’ 1997.
2. EU Directive 98/83/EC, ‘‘Water Quality Standards for Pesticides,’’ 1998.
3. Cody RB, Laramee JA, Durst HD. Anal. Chem. 2005, 77, 2297–302.
4. Song L, et al. Anal. Chem. 2009, 81, 10080–88.
5. Beck J, Yang C. Thermo Fisher Scientific Application Note, 2008.
6. Thermo Fisher Scientific, ‘‘Acclaim Trinity Mixed-Mode Columns,’’ Product Brochure.