Determination of acidic non-steroidal anti-inflammatory drugs in aquatic samples by liquid chromatography-triple quadrupole mass spectrometry combined with carbon nanotubes-based solid-phase extraction.

A solid-phase extraction (SPE) method based on multi-walled carbon nanotubes (CNT) was developed for the determination of 12 acidic non-steroidal anti-inflammatory drugs (NSAIDs) in surface waters and tap water. Pristine and functionalised CNTs were evaluated as sorbent materials. Batch experiments were used to optimise sorption and desorption conditions (sorbent type and amount, adsorption time, pH). The adsorption equilibrium was reached after 8 to 48 h duration, which increased with the pH of solution. Non-agglomerated pristine CNTs (20 mg) showed the most optimal adsorption (94 to 100%) for all of the analytes after a 30-min contact period in acidified water solutions (100 mL). The compounds retained at those conditions were recovered by 40 to 95% by using 5% ammonium hydroxide in methanol as the desorbing solution at ambient conditions. A comprehensive liquid chromatography coupled to triple quadrupole mass spectrometry (LC-QqQ-MS/MS) was used for the analysis of real water samples. The method showed sufficient recovery (65-125%) and good precision (2-14% relative standard deviation (RSD)). The limits of detection and quantification ranged between 0.01 and 1.3 ng L-1 and 0.04 and 3.9 ng L-1. Only diclofenac and ibuprofen were found in the analysed surface water samples from Latvia (n = 10) and Norway (n = 14). Diclofenac was found at 1.7-8.4 ng L-1 concentration in two samples of surface waters, whereas the concentrations of ibuprofen ranged between 1.0 and 9.2 ng L-1 in seven samples collected in Norway and 3.9-17 ng L-1 in three samples from Latvia.