Bar adsorptive microextraction coated with multi-walled carbon nanotube phases - Application for trace analysis of pharmaceuticals in environmental waters

Bar adsorptive microextraction devices were modified with multi-walled carbon nanotubes for the first time. A bar adsorptive microextraction method followed by microliquid desorption and high-performance liquid chromatography with diode array detection was developed for the determination of trace levels of ketoprofen, diclofenac, gemfibrozil and mefenamic acid in water samples. The mean parameters affecting the bar adsorptive microextraction and microliquid desorption efficiency were studied and optimized using a univariate optimization strategy. The methodology was validated in terms of linearity, limits of detection and quantification, recovery, intra- and inter-day precision, accuracy, and matrix effect. The developed method showed lower limits of quantification of 0.35 μg L⁻¹, calibration curves from 0.35 up to 1000.0 μg L⁻¹ and determination coefficients higher than 0.9917. Recoveries in tap, surface, sea and waste water samples at three spiking levels were between 70.2 and 117.3% for all the pharmaceuticals. The coefficients of variation values for intra- (n = 6) and inter-day precisions (n = 18) were below 9.7%. The proposed analytical methodology allowed preconcentration factors up to 250 and proved to be cost-effective, easy to operate and environmentally friendly.