Membrane-based Continuous SPE Online Fluorescence Analysis and Its Application to Rapid Detection of Tetracycline in Aquatic Environment

With the widespread detection of antibiotics in the environment, rapid online monitoring of trace tetracycline in water is of great significance for pollution early warning and risk assessment. To address the drawbacks of conventional analytical methods such as high-performance liquid chromatography, which involve expensive instruments, complex operation, and difficulty in achieving real-time on-site monitoring, this study develops an online detection technique and device based on membrane continuous solid-phase extraction coupled with fluorescence spectroscopy (CSPES). A mixed cellulose membrane is used to selectively enrich tetracycline, and the fluorescence signal on the membrane surface is collected in situ via a light source and an optical fiber probe. System parameters including the distance between the fiber probe and the membrane surface, vacuum pump pressure, and membrane material are optimized to achieve efficient spectral acquisition of tetracycline. By introducing a two-dimensional (2D) smoothing pretreatment method, a CSPES theoretical model is constructed and a quantitative relationship among fluorescence intensity, time, and concentration is established. The calibration curve exhibits a linear correlation coefficient of R² = 0.996 6, confirming the applicability of the CSPES model for trace analysis. The method provides a limit of detection of 0.1 μg/L and a linear range of 0.5-5 μg/L. For the prediction of unknown samples, the relative error is less than 2%, and the relative standard deviation (RSD) ranges from 1.27% to 2.08%, demonstrating good quantitative accuracy and repeatability. The method is further applied to spiked drinking water, tap water, and river water samples, yielding recoveries of 95.27%-105.8% with RSDs (n = 5) of 1.65%-5.06%, which are consistent with the results obtained by HPLC. This indicates that the device has good adaptability and anti-interference capability in complex water matrices. Compared with traditional detection approaches, the CSPES online detection system features a compact structure, a high degree of automation, fast analysis, and low cost. It provides an efficient, sensitive and scalable technical solution for on-site online monitoring of tetracycline and other antibiotic pollutants and lays a methodological foundation for future extension to simultaneous multi-component detection and intelligent environmental monitoring systems.