Extraction of phthalic acid esters from soil samples using aqueous room temperature sonication coupled to bubble-in-drop single-drop microextraction

As a pre-concentration technique, bubble-in-drop, single-drop microextraction has received considerably less attention than its counterparts despite its efficiency, simplicity, eco-friendliness and affordability. Herein, we present the development of this method using a non-chlorinated solvent–dodecane and its application in the extraction and pre-concentration of 17 phthalic acid esters (PAEs) from aqueous samples. The optimised method used 1 µL dodecane and 0.5 µL air bubble, 5% NaCl and a static extraction time of 20 min. The method demonstrates sufficient linearity (R² ≥ 0.9635) and repeatability (%RSD ≤ 20% for n = 27) with the estimated limit of detection in the range 0.23–0.69 ng/mL using the statistical approach for a 17-component standard mixture of the esters. Enrichment factors ranged from 10 to 38 for all the esters, except dimethyl phthalate that did not show any preference to the dodecane solvent used in the study. Application of the technique to contaminated soil samples detected only one ester–bis-(2-ethylhexyl) phthalate (0.62 ng/g of soil), the most common PAE found in most solid waste dumpsite studies due to its wide use in everyday life. The study further highlights the difficulty of extracting the phthalates from soil samples owing to their susceptibility to hydrolysis thereby lowering their extractability from the aqueous solutions which is a prime requirement for the liquid-based microextraction techniques.