Comparison of Mold Odor Analysis in Water by Purge and Trap (PTC) and Solid-Phase Microextraction (SPME)

Significance of the Topic

A reliable detection of geosmin and 2-methylisoborneol at part-per-trillion levels is critical for maintaining consumer confidence in drinking water quality. These microbial by-products impart musty odors at concentrations well below human sensory thresholds. Implementing robust analytical methods ensures rapid identification and mitigation of taste and odor issues, safeguarding both public perception and regulatory compliance.

Objectives and Study Overview

This study compares two headspace concentration techniques—Purge and Trap concentrator (PTC) versus Solid-Phase Microextraction (SPME)—coupled with GC/MS analysis for trace mold odor compounds in water. Key performance metrics include turnaround time, linearity, accuracy, precision, method detection limits (MDLs), and carryover.

Methodology and Instrumentation

Sample Preparation and Extraction

• SPME: A coated fiber immersed in a water sample for 30–60 min, followed by thermal desorption in a GC injection port; requires fiber conditioning and specialized liners.
• PTC with AQUATek 100 Autosampler: Automated loading of 5 mL or 25 mL aliquots into a 100-position carousel; analytes purged onto a proprietary sorbent trap and thermally desorbed to GC/MS.

Instrumentation Used

PTC and Autosampler

• Stratum Purge and Trap Concentrator with Teledyne Tekmar #9 trap
• AQUATek 100 Waters-only Autosampler

GC/MS System

• Agilent 7890A GC with Restek Rtx-624 column (20 m × 0.18 mm × 1.0 µm)
• Agilent 5975C MSD in SIM mode (selected ions: 95, 107, 112, 124, 125, 137, 151, 152, 195, 197, 212)

Key Operating Conditions

• Oven program: 40 °C (2 min) → 160 °C @ 16 °C/min → 240 °C @ 20 °C/min
• Purge: 10 min at 20 °C, 100 mL/min; dry purge: 5 min at 20 °C, 45 mL/min
• Desorb: 2 min at 250 °C, 300 mL/min; bake: 5 min at 260 °C, 250 mL/min

Main Results and Discussion

Calibration and Sensitivity

• Linear calibration from 1 ppt to 100 ppt for geosmin, 2-MIB, IBMP, and 2,4,6-trichloroanisole (r² ≥ 0.9998)
• MDLs below 0.05 ppt for all target analytes
• Carryover under 0.5% after 100 ppt standard

Precision and Accuracy

• %RSD ≤ 6.5% across calibration range
• 24-hour continuing calibration verification with ≥ 80% recovery in 10% NaCl matrix

Comparison with SPME

• PTC provided equal or superior linearity, sensitivity, and precision
• Fully automated sample preparation eliminated specialized consumables and fiber handling
• Continuous operation increased throughput by avoiding long fiber equilibration and conditioning steps

Benefits and Practical Applications of the Method

The PTC–AQUATek 100 approach offers:

• Complete automation of liquid sample extraction, reducing hands-on time and variability
• No requirement for specialized fibers or liners, lowering consumable costs
• Capability to run multiple analyses (mold odor and VOCs) sequentially without hardware changes
• Scalability for high-throughput laboratories monitoring water quality under EPA Method 524.2

Future Trends and Applications

Emerging opportunities include integrating PTC systems with high-resolution mass spectrometry for simultaneous non-target screening of odorants and emerging contaminants. Development of novel sorbent materials may extend analyte coverage and enhance trap capacity. Real-time monitoring modules linked to automated sampling platforms could enable online odor surveillance in distribution networks.

Conclusion

The Stratum PTC coupled to an AQUATek 100 Autosampler and GC/MS in SIM mode delivers robust, automated analysis of trace mold odor compounds in water. It surpasses traditional SPME in sensitivity, throughput, and operational simplicity, while meeting or exceeding EPA Method 524.2 criteria. The method’s adaptability to simultaneous VOC and odorant monitoring streamlines water quality assessment, offering significant benefits for laboratories and water utilities.

Reference

1. USEPA Method 524.2, Revision 4.1, 1995
2. Supelco, Solid-Phase Microextraction of Odors in Drinking Water for Analysis by GC/MS, 2002
3. Thermo Scientific, Determination of Geosmin and 2-MIB in Drinking Water by SPME-PTV-GC/MS, 2007