Determination of Theophylline Across Biological, Environmental and Food Matrices Using Liquid-Phase Microextraction Coupled with LC-MS/MS

Theophylline represents a significant public health challenge due to its dual acute and chronic toxicity resulting from therapeutic, environmental, and dietary exposures. Effective monitoring across the bio-environmental–food triad requires analytical methods that are highly sensitive, universally applicable, and capable of overcoming complex matrix interferences. This study introduces a flat membrane-based liquid-phase microextraction (LPME) technique combined with LC–MS/MS for the determination of theophylline in diverse matrices. The method eliminates the need for specialized adsorbents or equipment, offering a simple and cost-effective solution for high-throughput sample clean-up. Under optimized conditions, the method demonstrated exceptional sensitivity (LOD: 0.2 ng mL−1) and a wide linear range (0.01–10 μg mL−1). It was successfully applied to plasma, urine, hospital sewage, and green tea, providing accurate (recoveries of 86.7–111.3%) and reproducible (RSD < 10%) results across all matrices. This unified and robust approach effectively addresses matrix interferences and provides a reliable tool for the monitoring and risk assessment of theophylline across multiple domains.