Vial-wall sorptive extraction (VWSE), in which a layer of sorbent covers the inner wall of a vial, sampling tube or bottle [1], is emerging as an alternative to other solid-phase extraction setups. This approach is user-friendly and couples sampling and extraction, offering the possibility of on-site monitoring and providing a greener sample treatment when biochar is used as a carbon-based sorbent. This is possible thanks to its ease of preparation by pyrolysis, the low-cost and large availability of precursors, as well as the abundance of aliphatic and aromatic moieties bearing oxygenated groups that widen the sorbent affinity to a variety of analytes [2].
In this work, char derived from pumpkin peel, immobilized in a Falcon® tube (15 mL capacity), showed a good sorption capability towards steroid hormones in fresh and brackish waters and wastewaters, for at least 20 sorption/desorption cycles, with complete analytes’ elution in ethanol. The final procedure allows a multiclass preconcentration at the trace levels from a few-mL samples, in agreement with Green Analytical Chemistry (GAC) and Green Sample Preparation (GSP) Principles, as further pointed out by three dedicated software for greenness assessment [1].
The applicability of the biochar-based VWSE was also assessed in a miniaturized format (1.5 mL Eppendorf® tubes) for the analysis of gastric cancer biomarkers (e.g., bile acids) in urine. Preliminary data using synthetic urine (1 mL), under orbital shaking, show that the sorbent (28 mg ± 5 mg) uptakes the analytes under acidic conditions via formic/formate buffering (pH ~3.5). Experiments are ongoing to evaluate the extraction efficiency in real human urine, and to refine the elution using ethanol, as a safe and environmentally friendly solvent.
The herein developed sample treatments are successfully applied to simultaneous extraction/cleanup/enrichment before HPLC-MS/MS analysis (Multiple Reaction Monitoring Mode), which entails NH4F (1 mM) as additive for the aqueous phase to increase sensitivity of the target analytes, allowing the chromatographic separation of organic analytes with a wide range of logP values (1.5-4.9).
Merlo F., Speltini A., Profumo A., Advances in Sample Preparation, 15 (2025), 100203. https://doi.org/10.1016/j.sampre.2025.100203
Merlo F., Tassi L., Milanese C., Profumo A., Speltini A., Green Analytical Chemistry, 15 (2025), 100298, https://doi.org/10.1016/j.greeac.2025.100298