Analysis of BTEX in Water with a CAR(WR)/PDMS 95 μm SPME Fiber

Significance of the Topic

Volatile aromatic hydrocarbons such as benzene, toluene, ethylbenzene and xylenes (BTEX), as well as methyl tert-butyl ether (MTBE), frequently contaminate drinking water due to fuel leaks and industrial discharges
These compounds are regulated at low parts-per-billion levels because of their toxicity and widespread occurrence
A rapid, sensitive and solvent-free analytical approach is essential for routine monitoring and compliance testing

Objectives and Overview

This study evaluates the performance of a CAR(WR)/PDMS 95 µm solid-phase microextraction (SPME) fiber for headspace sampling of BTEX and MTBE in water
Key goals include assessing linearity, calibration accuracy, detection and quantitation limits, retention time stability and reproducibility under automated conditions

Methodology and Instrumentation

Sample Preparation and Calibration

• Salt addition: 4 ± 0.05 g NaCl in 20 mL headspace vials enhances analyte partitioning
• Internal standard (ISTD) solution: dibromofluoromethane, toluene-d8 and 4-bromofluorobenzene at 2.5 µg/mL
• Calibration standards: MTBE, benzene, toluene, ethylbenzene, m-xylene, p-xylene and o-xylene at 2.5 µg/mL stock, diluted to 1.25–6.25 µg/L

SPME Headspace Extraction

• Fiber: CAR(WR)/PDMS 95 µm
• Incubation: 5 min at 40 °C, agitation at 1 000 rpm
• Extraction: 24 min at 40 °C with no additional agitator

Gas Chromatography and Detection

• Instrumentation: Automated PAL RTC rail with Agilent 7890B GC, 5977B MSD and FID detectors
• Column: CP-Sil 5 CB, 30 m × 0.25 mm × 1.0 µm
• Injection: splitless at 290 °C; oven program from 30 °C (4 min) to 100 °C at 4 °C/min
• MS conditions: scan mode, transfer line 260 °C, source 280 °C, quadrupole 150 °C
• FID conditions: H2 40 mL/min, air 400 mL/min, makeup He 25 mL/min at 300 °C

Main Results and Discussion

Linearity and Calibration Accuracy

• All analytes showed linear responses with R2 ≥ 0.99
• Calibration accuracy ranged from 98.8 % to 100.9 % across 1.25–6.25 µg/L levels

Retention Time Stability

• Average RT RSDs were below 0.4 %, confirming reproducible chromatography

Detection and Quantitation Limits

• Method detection limits (MDLs) were below 0.80 ppb for all compounds
• Limits of quantitation (LOQs) were below 2.39 ppb

Benefits and Practical Applications of the Method

The headspace SPME approach requires no solvents and minimizes sample handling
High sensitivity and automated sampling enable rapid throughput in drinking water monitoring labs
Selective fiber coating enhances extraction of low-molecular-weight volatiles, improving method robustness

Future Trends and Potential Applications

Integration with portable GC-MS systems for field screening of VOCs in environmental waters
Development of multi-fiber coatings to expand the target analyte range
Implementation of online SPME-GC-MS workflows for real-time process monitoring and compliance testing

Conclusion

The CAR(WR)/PDMS 95 µm SPME fiber combined with automated headspace extraction and GC/MS-FID detection provides a reliable, sensitive and solvent-free method for BTEX and MTBE analysis in water
Linearity, accuracy, retention stability and low detection limits meet regulatory and laboratory quality requirements

Used Instrumentation

• PAL RTC rail sampler
• CAR(WR)/PDMS 95 µm SPME fiber
• Agilent 7890B GC system
• Agilent 5977B High Efficiency Source GC/MSD
• Agilent FID detector
• CP-Sil 5 CB capillary column

References

1. Almeida C. M. M.; Vilas Boas L., Journal of Environmental Monitoring, 2004, 6, 80–88
2. American Water Works Association, Water Quality & Treatment: A Handbook of Community Water Supplies, 5th ed., McGraw-Hill, 1999
3. Vassalli G., Agilent Technologies Application Note SI-01251, 2010