Flow-through dispersed carbon nanofiber-based microsolid-phase extraction coupled to liquid chromatography for automatic determination of trace levels of priority environmental pollutants

Abstract

Handling of carbon nanoparticles as sorptive materials in a flow-through packed-bed mode has been to date hampered by undue pressure drop and deteriorated retention efficiency because of nanoparticle bundling and entanglement. To surmount this limitation, a dedicated stirred-flow sorptive microchamber integrated in a fully automated sequential injection (SI) assembly is herein proposed for expedient handling and reuse of carbon nanoparticles in microsolid-phase extraction (μSPE) procedures. The assembled setup features automatic uptake, preconcentration, and retrieval of target organic species using dispersed nanoparticles as a front-end to liquid chromatographic (LC) assays. Chlorotriazine residues (atrazine, simazine, and propazine) and dealkylated metabolites thereof (deisopropyltriazine (DIA) and deethylatrazine (DEA)) were selected as model compounds because of their electron-poor aromatic structure and potentially strong π-π interactions with electron-rich sorptive materials. The effect of several parameters on the analytical performance including the type and amount of nanoparticles (carbon nanofibers (CNFs), multiwalled carbon nanotubes (MWCNTs) and oxidized carbon nanotubes (MWCNT-COOH), the sample volume (breakthrough volume), the nature and volume of eluent, and the interface between the sample processing module and LC was explored in detail. Using dispersed CNFs at-line coupled to LC, absolute recovery percentages for 10 mL sample percolation were >94% for the overall herbicides with enrichment factors of ca. 20, limits of detection (S/N = 3) of 0.004-0.03 ng mL(-1), limits of quantification (S/N = 10) of 0.01-0.09 ng mL(-1) and repeatability within the range 0.5-1.8%. The SI-CNF-LC hyphenated system was harnessed to the analysis of not merely untreated environmental waters at concentration levels below those endorsed by the current EU Water Framework Directives but to crude soil extracts for which CNF reuse with no loss of retention efficiency was proven feasible by resorting to appropriate automatic regeneration procedures and internal standardization.