Activated carbon from avocado seed as sorbent phase for microextraction technologies: activation, characterization,...

According to green analytical chemistry principles, the use of agricultural byproducts as sorbent phases is an interesting topic due to their lignocellulosic origin, as they are biodegradable and inexpensive. To the best of our knowledge, this is the first study in which avocado seed and avocado seed activated carbon are proposed as sustainable sorbents for solid-phase microextraction technologies, which were used to assess the proof of concept. Rotating disk sorptive extraction (RDSE) was used as a model technology and ibuprofen (Ibu) and 1-hydroxy-ibuprofen (1-OH-Ibu) as representative analytes. It was found that activated carbon (AC) prepared at 600 °C with an impregnation ratio (raw material/activating agent (ZnCl₂), w/w) of 1:1.2 had better extraction efficiency than other ACs obtained at different temperatures, impregnation ratios, and activating agents (K₂CO₃). Characterization revealed several differences between natural avocado seed, biochar prepared at 600 °C, and selected AC since the typical functional groups of the natural starting material begin to disappear with pyrolysis and increasing the surface area and pore volume, suggesting that the main interactions between analytes and the sorbent material are pore filling and π-π stacking. By using this AC as the sorbent phase, the optimal extraction conditions in RDSE were as follows: the use of 50 mg of sorbent in the disk, 30 mL of sample volume, pH 4, 90 min of extraction time at a rotation velocity of the disk of 2000 rpm, and methanol as the elution solvent. The extracts were analyzed via gas chromatography coupled to mass spectrometry (GC-MS). The method provided limits of detection of 0.23 and 0.07 µg L^-1 and recoveries of 81% and 91% for Ibu and 1-OH-Ibu, respectively. When comparing the extraction efficiency of the selected activated carbon with those provided by Oasis® HLB and C18 in RDSE, nonsignificant differences were observed, indicating that avocado seed activated carbon is a suitable alternative to these commercial materials.