Determination of Henry's law constants for low volatile mixed halogenated anisoles using solid-phase microextraction

Trihalogenated anisoles (THAs) are present in drinking water at low concentrations and are linked to odor complaints. Understanding their behavior requires knowledge of Henry's law constants (K_H), which influence how these compounds move from water to air. Prior research has shown that THAs can cause noticeable odors, but the specific mechanisms of their volatility remain unclear. No prior work had resolved the K_H values for mixed halogenated anisoles using precise methods. This gap motivated the need for accurate K_H measurements. Existing methods are limited in their applicability to low-volatility compounds like THAs. The study addresses this limitation by using EPICS-SPME. The need for a narrow headspace/water volume ratio was identified as a key challenge. This study provides a framework for measuring K_H under controlled conditions.

The aim of this study is to determine Henry's law constants (K_H) for trihalogenated anisoles (THAs) using a precise analytical approach. THAs are low-volatility compounds that contribute to odor events in drinking water. The specific problem addressed is the lack of accurate K_H values for these compounds. The motivation stems from the need to better predict and manage odor episodes in water supplies. The study focuses on THAs with mixed halogen substitutions. The researchers propose using equilibration partitioning in a closed system and headspace microextraction (EPICS-SPME). This method allows for controlled measurement of K_H at specific temperatures. The goal is to provide reliable data for environmental and water quality modeling.

The study employs equilibration partitioning in a closed system (EPICS) combined with solid-phase microextraction (SPME) to determine Henry's law constants (K_H) for trihalogenated anisoles (THAs). The method involves equilibrating THAs in water and measuring their partitioning into the vapor phase. Two theoretical approaches, Ramachandran and Dewulf, are used to calculate K_H values. The experiments are conducted at two temperatures: 45°C and 22°C. A narrow headspace/water volume ratio range (80/1 to 8/1) is maintained to ensure accurate measurements. The Ramachandran method relies on theoretical relationships to derive K_H. The Dewulf method provides an alternative calculation based on partitioning data. Both methods are validated for their linearity and reproducibility.

The study reports Henry's law constants (K_H) for trihalogenated anisoles (THAs) at 45°C and 22°C using EPICS-SPME. The Ramachandran method yielded linearity (r²) values ranging from 0.9276 to 0.9989. The Dewulf method showed lower variability, with R.S.D.% below 20% for five replicates. These results suggest both methods are suitable for THAs under controlled conditions. At 45°C, K_H values were higher than at 22°C, indicating increased volatility with temperature. The study confirms that a narrow headspace/water volume ratio is essential for accurate K_H measurements. The calculated K_H values provide a reliable basis for predicting THA behavior in water systems. These findings support the use of EPICS-SPME for low-volatility compounds.

The study concludes that equilibration partitioning in a closed system and headspace microextraction (EPICS-SPME) is a viable method for determining Henry's law constants (K_H) for trihalogenated anisoles (THAs). Both the Ramachandran and Dewulf methods were found to be effective under the specified conditions. The linearity of the Ramachandran method ranged from 0.9276 to 0.9989, while the Dewulf method showed variability below 20%. These findings suggest that the methods can be reliably applied to THAs. The study confirms the importance of maintaining a narrow headspace/water volume ratio for accurate measurements. The results support the use of EPICS-SPME for low-volatility compounds in environmental studies. The authors propose that these K_H values can aid in predicting odor events in water systems. The findings contribute to the understanding of THA behavior in aqueous environments.