Online hyphenation of in-capillary aptamer-functionalized solid-phase microextraction and extraction nanoelectrospray ionization for miniature mass spectrometry analysis

In this study, an integrated experimental protocol has been developed, combining in-capillary aptamer-functionalized solid-phase microextraction (SPME), extraction nanoelectrospray ionization (nanoESI), and miniature MS analysis. The established method was applied to analyze caffeine in electronic cigarette liquid and beverage samples as proof-of-concept demonstrations. A custom SPME strip fabricated with caffeine-binding aptamers was prepared with an immobilization density of up to 0.812 nmol cm^-2. Critical parameters affecting the effects of extraction, desorption, and ionization were optimized. A novel transition ion ratio-based strategy with enhanced quantitation accuracy was developed. The analytical performance of the proposed method was evaluated under optimized conditions. Acceptable recoveries of 87.5–111.5% with relative standard deviations of 3.1–6.1% and satisfactory sensitivity with limits of detection of 1.5 and 3 ng mL^-1 and limits of quantitation of 5 and 10 ng mL^-1 were obtained, respectively. The developed approach demonstrates a promising potential for rapid on-site applications with appealing analytical performance and efficiency.

In this study, the online hyphenation of in-capillary aptamer-functionalized SPME, extraction nanoESI, and a miniature mass spectrometer was explored. Sample extraction, enrichment, desorption, ionization, and detection were streamlined. Proof-of-concept experiments were performed for the rapid onsite detection of caffeine in electronic cigarette liquid and beverage samples. A custom SPME strip was prepared by immobilizing specific aptamers on a gold-sputtered aluminum foil with a high coverage density, allowing the selective recognition and enrichment of caffeine analytes. Simultaneous desorption and ionization of enriched analytes were achieved using extraction nanoESI with a pulled glass capillary. A novel TIR-based quantitation strategy was implemented for miniature MS analysis, exhibiting enhanced linearity and quantitation robustness compared to those of traditional external standard calibration. Our method demonstrates great potential for outside-the-laboratory applications, enabling rapid on-site chemical analysis with satisfactory performance.