Stir Bar Sorptive Extraction: Recovery of Organic Acids and Amines
The determination of volatile and semi-volatile compounds in aqueous solutions using Stir Bar Sorptive Extraction (SBSE) as the extraction step is gaining acceptance in a wide variety of application areas including water, beverages, consumer products and environmental. It has been shown to be simple, sensitive, quantitative, and can often eliminate cumbersome solvent extraction or other sample preparation steps. Efficiency of partitioning into the polydimethylsiloxane (PDMS) phase on the stir bar can be predicted based on the known analyte partitioning between octanol and water as described by the octanol-water partition coefficient Kow. This prediction usually works well for most compounds, but can overestimate recovery of ionizable compounds like organic acids and amines since only the neutral form can be extracted into the bar. SBSE of organic acids and amines is evaluated from simple aqueous solutions as well as at pH extremes. Extraction behavior as a function of pH is correlated to published compound dissociation constants. Strategies to enhance extraction efficiency of ionizable compounds are discussed.