Expanding the applicability of cork as extraction phase for disposable pipette extraction in multiresidue analysis of pharmaceuticals in urine samples.

In this paper, cork is proposed as a natural and renewable material for the extraction phase in disposable pipette extraction to be applied in the multiresidue determination of pharmaceuticals in human urine by HPLC with diode array detection. The compounds carbamazepine, losartan, ketoprofen, 17‑β‑estradiol, naproxen, diazepam, 17‑α‑ethinylestradiol, estrone, diclofenac and ibuprofen were studied. A known amount (5 mg) of cork, with a size of 200 mesh, was inserted into a pipette tip. The method optimization was carried out with univariate and multivariate approaches. The optimized conditions were sample pH adjusted to 3, urine dilution factor of 40 (158 μL of urine diluted in 6.142 mL of ultrapure water), 9 extraction cycles each performed with 700 μL of sample, and extraction time of 10 s per cycle. Desorption was performed with 85 μL of methanol applying 6 cycles of 10 s each using the same solvent aliquot. For the clean-up step, 4 cycles were carried out each with 200 μL of methanol. The limits of quantification varied from 5 to 10 μg L-1 with determination coefficients higher than 0.9919 for the calibration curves for all the analytes. Intra-day and inter-day precision and relative recovery from urine samples donated by two volunteers were assessed based on three spiked concentrations. The analyte relative recoveries ranged from 65 to 117% (n = 3) for the two samples. Intra-day precision ranged from 1.2 to 17% (n = 3) and inter-day precision varied from 11 to 21% (n = 9).