New SBSE–HPLC-DAD Method Proposed to Analyze Trace PCBs in Environmental Waters

A study published in the Journal of Chromatography A, from a team of researchers in the Department of Chemistry at Wuhan University in Wuhan, China, has detailed a new method used successfully in the detection of trace polychlorinated biphenyls (PCBs) in the Yangtze River and East Lake in Wuhan (1).

China's largest rivers: the Yangtze | Image Credit: © gui yong nian - stock.adobe.com

The approach improves upon the preferred pretreatment of stir bar sorptive extraction (SBSE), which is considered superior to other microextraction techniques when it comes to enriching trace PCBs because of its large adsorption capacity, low consumption of organic solvents, simple phase separation process, and an avoidance of the competitive adsorption of target analytes on magnetons such as with solid-phase microextraction (SPME). High performance liquid chromatography (HPLC) has been widely used to analyze trace PCBs regardless of the microextraction deployed, whether that be liquid-phase microextraction (LPME), magnetic solid-phase extraction (MSPE), SPME, or SBSE. In this study, diode array detection (DAD) was added to the HPLC process.

Solid-phase microextraction (SPME) is a technique used for sample preparation in which a fiber coated with a stationary phase is used to extract analytes from a sample. In the case of PCB analysis, the fiber may be coated with various types of polydimethylsiloxane (PDMS) stationary phase. The fiber is inserted into the sample and left to equilibrate for a period of time, during which the analytes partition between the sample and the fiber. After extraction, the fiber is removed and inserted into an HPLC instrument for analysis, where the analytes are desorbed from the fiber and separated using chromatography. This technique offers advantages over traditional extraction methods, such as reduced sample volume and solvent requirements, and improved sensitivity and selectivity.

According to the researchers, fast, sensitive, and accurate quantification of trace PCBs in environmental samples is crucial to evaluating human health risks. While PCBs have many common applications such as plasticizers, flame retardants, coolants, and lubricants, they are persistent organic pollutants that do not easily biodegrade, photodegrade, or chemically decompose. When accumulated in the human body, they can have carcinogenic, teratogenic, and mutagenic effects including endocrine and immune function disorders as well as cancer.

The effectiveness of the combined methods of analysis in this study was attributed in part to the porous material, specifically a porous aromatic framework (PAF), developed as the coating component for analyte extraction by SBSE. With the target PCBs having molecular size and structure of 1.1 to 1.4 nm in length, 0.7 to 0.8 nm in width, and 0.5 to 0.8 nm in thickness, PAF-47 containing a benzene ring structure with a pore size of 0.5 to 0.9 nm and 1.2 to 1.4 nm was chosen and synthesized through the Suzuki coupling reaction to prepare PAF-47-polydimethylsiloxane (PDMS) coated stir bars by a sol-gel method, making the PAF-47 evenly dispersed in the PDMS.

The PAF-47-PDMS coating applied in conjunction with SBSE was found to provide high extraction recovery for five PCBs in the relatively short time of 60 minutes, versus 12 or 24 hours for commercial PDMS coating. The extraction recovery expressed as a ratio of actual enrichment factor (EF) to theoretical EF was between 77.6% and 90.6%. After HPLC-DAD analysis, the limits of detection for the five PCBs were within 44 to 70 ng/L with actual EF of 64.0 to 71.5-fold where maximal EF was 83.3-fold.

Applied to the environmental waters of the Yangtze River and East Lake, recovery rates were between 81.0% and 113%, and 86% and 111%, respectively, further demonstrating the significant improvements in extraction recovery made possible by integrating the PAF-47-PDMS coating into the SBSE–HPLC-DAD method.

Reference

(1) Zhang, Q.; Yao, X.; He, M.; et al. Porous aromatic framework/polydimethylsiloxane coated stir bar sorptive extraction coupled with high performance liquid chromatography-diode array detection of trace polychlorinated biphenyls analysis in environmental waters. J. Chromatogr. A 2023, 1688, 463709. DOI: 10.1016/j.chroma.2022.463709