Oxidized Buckypaper for Stir-Disc Solid Phase Extraction: Evaluation of Several Classes of Environmental Pollutants Recovered from Surface Water Samples

This paper describes, for the first time, the use of oxidized buckypaper (BP) as a sorbent membrane of a stir-disc solid phase extraction module. The original device, consisting of a BP disc (d = 34 mm) enveloped in a polypropylene mesh pouch, was designed to extract organic micropollutants (OMPs) from environmental water samples in dynamic mode. High-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) was used to analyze the extracts. Several classes of pesticides and pharmaceuticals were chosen as model compounds to evaluate key parameters affecting the recovery rates. To this end, the effects of adsorption time, desorption time, stirring speed, type and volume of solvent, and sample volume were thoroughly examined. After optimization, a novel and in-depth study was conducted to find a correlation between physicochemical properties of the analytes and extraction yields. Recoveries were mainly governed by a combination of logP and pK_a values. As indicated, hydrophilic compounds with logP < 1 showed poor affinity for the oxidized BP, compounds having logP > 1 exhibited recoveries ranging between 50% and 100% depending on their pK_a, while compounds with pK_a between 6 and 7.5 gave low yields irrespective of their logP. The analytical method was also validated and tested as large scale screening method of OMPs in surface waters. The analysis of real samples revealed the presence of some nonsteroidal anti-inflammatory drugs, sulfonamides, and pesticides at low ng L^–1 concentration levels with relative standard deviations lower than 8%.