Improved method for the storage of groundwater samples containing volatile organic analytes

Area of Science:

• Environmental Chemistry
• Analytical Chemistry

Background:

• Standard methods for analyzing volatile organic compounds (VOCs) in water often use Teflon septa in glass vials.
• Teflon's inertness is generally assumed, but its sorption properties for specific analytes require careful evaluation.

Purpose of the Study:

• To investigate the sorption of various volatile organic analytes by Teflon septa in standard sample vials.
• To assess the impact of this sorption on the accuracy of volatile petroleum hydrocarbon measurements.
• To develop and validate an alternative storage method to prevent analyte loss.

Main Methods:

• Analyzed volatile organic analytes including alkanes, aromatics, and chloroethenes in laboratory solutions and field samples.
• Evaluated analyte concentration changes in standard Teflon-lined vials stored at room temperature and 4°C over time.
• Tested an alternative storage protocol using lead foil septa and a sodium phosphate preservative.

Main Results:

• Significant loss (>10%) of n-alkanes and isoalkanes occurred within 24 hours at room temperature.
• Aliphatic analyte losses (>10%) were also observed over 21 days at 4°C.
• The alternative storage method successfully prevented analyte loss for at least 21 days at room temperature.

Conclusions:

• Sorption by Teflon septa can significantly reduce the accuracy of volatile petroleum hydrocarbon measurements in water samples.
• Traditional storage methods using Teflon septa are inadequate for preserving the integrity of certain volatile organic analytes.
• A novel storage protocol employing lead foil septa and a sodium phosphate preservative offers a reliable alternative for sample preservation.