A novel sorbent based on carbon nanotube/amino-functionalized sol-gel for the headspace solid-phase microextraction of α-bisabolol from medicinal plant samples using experimental design

A novel sol-gel coating on a stainless-steel fiber was developed for the first time for the headspace solid-phase microextraction and determination of α-bisabolol with gas chromatography and flame ionization detection. The parameters influencing the efficiency of solid-phase microextraction process, such as extraction time and temperature, pH, and ionic strength, were optimized by the experimental design method. Under optimized conditions, the linear range was between 0.0027 and 100 μg/mL. The relative standard deviations determined at 0.01 and 1.0 μg/mL concentration levels (n = 3), respectively, were as follows: intraday relative standard deviations 3.4 and 3.3%; interday relative standard deviations 5.0 and 4.3%; and fiber-to-fiber relative standard deviations 6.0 and 3.5%. The relative recovery values were 90.3 and 101.4% at 0.01 and 1.0 μg/mL spiking levels, respectively. The proposed method was successfully applied to various real samples containing α-bisabolol.

Sol-gel niobia sorbent with a positively charged octadecyl ligand providing enhanced enrichment of nucleotides and organophosphorus pesticides in capillary microextraction for online HPLC analysis

A niobia-based sol-gel organic-inorganic hybrid sorbent carrying a positively charged C₁₈ ligand (Nb₂ O₅ -C₁₈ (+ve)) was synthesized to achieve enhanced enrichment capability in capillary microextraction of organophosphorus compounds (which include organophosphorus pesticides and nucleotides) before their online analysis by high-performance liquid chromatography. The sorbent was designed to simultaneously provide three different types of molecular level interactions: electrostatic, Lewis acid-base, and van der Waals interactions. To understand relative contributions of various molecular level analyte-sorbent interactions in the extraction process, two other sol-gel niobia sorbents were also created: (a) a purely inorganic sol-gel niobia sorbent (Nb₂ O₅ ) and (b) an organic-inorganic hybrid sol-gel niobia sorbent carrying an electrically neutral-bonded octadecyl ligand (Nb₂ O₅ -C₁₈ ). The extraction efficiency of the created sol-gel niobia sorbent (Nb₂ O₅ -C₁₈ (+ve)) was compared with that of analogously designed and synthesized titania-based sol-gel sorbent (TiO₂ -C₁₈ (+ve)), taking into consideration that titania-based sorbents present state-of-the-art extraction media for organophosphorus compounds. In capillary microextraction with high-performance liquid chromatography analysis, Nb₂ O₅ -C₁₈ (+ve) had shown 40-50% higher specific extraction values (a measure of extraction efficiency) over that of TiO₂ -C₁₈ (+ve). Compared to TiO₂ -C₁₈ (+ve), Nb₂ O₅ -C₁₈ (+ve) also provided superior analyte desorption efficiency (96 vs. 90%) during the online release of the extracted organophosphorus pesticides from the sorbent coating in the capillary microextraction capillary to the chromatographic column using reversed-phase high-performance liquid chromatography mobile phase.