The combination of solid-phase micro-extraction (SPME) with infrared (IR) attenuated total reflection (ATR) spectroscopic methods provides a fast and convenient way to detect organic compounds in aqueous solutions. In an effort to overcome the limitation of commercially available polymers, polystyrene (PS) was derivatized with different alkyl groups chain lengths to increase the performance of SPME-IR/ATR in detection of various aromatic compounds in aqueous solutions. The alkylated PS provides higher extraction efficiency and speed of diffusion in analysis of aromatic compounds than the commonly used polymers in SPME-IR/ATR methods. The increase of extraction efficiency is mainly caused by the pi - pi interaction between the phenyl rings of PS and the aromatic compounds. Meanwhile, the high rate of diffusion in the SPME phase is due to the lower crystallinity after alkylation. Results from analysis of different polarity aromatic compounds indicated that alkylated PS provides both a higher partition coefficient and a faster diffusion rate for the examined aromatic compounds. Better extraction performance of longer chain length PS was observed for low-polarity aromatic compounds. For higher polarity aromatic compounds, the increased chain length reduces the extraction efficiency in detection of this type of compound. This observation may reveal that the pi - pi interaction is more important in attraction of medium to polar aromatic compounds.
Jyisy Yang and Yuh-Shenq Huang, "IR Chemical Sensor for Detection of Aromatic Compounds in Aqueous Solutions Using Alkylated Polystyrene-Coated ATR Waveguides," Appl. Spectrosc. 54, 202-208 (2000)