Analysis of lipopolysaccharides by coupling microscale solid-phase extraction with capillary electrophoresis-laser induced fluorescence

Abstract

Lipopolysaccharides (LPS), also known as endotoxins, can be released into the environment when the bacteria’s cell wall breaks apart, which induces inflammatory responses in humans at amounts of 1–10 ng kg−1. This paper reports on the development and optimization of a novel analytical method for the analysis of LPS based on the coupled use of a laboratory–made microscale solid-phase extraction (μSPE) device for the purification and enrichment of LPS before fluorescent dye derivatization and lastly capillary electrophoresis with laser-induced fluorescence (CE-LIF) for separation and detection. In this work, the limits of detection and quantification of Klebsiella pneumoniae (KP)-LPS were found to reach 1.32 ng mL−1 and 4.39 ng mL−1, respectively with a linear dynamic range of 0.125–0.625 mg L−1 and a relative standard deviation of 0.9% in migration time. Scanning electron microscopy analysis clearly supports the successful entrapment of KP-LPS within the sorbent before elution. In contrast to other LPS extraction methods, the optimized μSPE-based method coupled with CE-LIF provides the following advantages: small sample amount for sensitive and selective detection in CE-LIF (μSPE preconcentration factor of 23 times), reduced volumes of organic solvents used (175–225 µL), high recovery rate of 98%, as well as portability for on-site extraction and quantification of analytes. The method was successfully applied in the analysis of three types of real water samples (i.e. deionized water, secondary effluent and raw sewage). Raw sewage was found to contain the highest KP-LPS amount of 12.5 ng mL−1 followed by secondary effluent of 7.3 ng mL−1.