Simultaneous determination of naproxen, ibuprofen and diclofenac in wastewater using solid-phase extraction with high performance liquid chromatography

The occurrence and removal efficiency for naproxen, ibuprofen and diclofenac in two of eThekwini Municipality's wastewater treatment plants (WWTPs), Kingsburgh and Umbilo, were investigated. This paper describes a simple method that can be used routinely for the simultaneous determination of such compounds in the influent and effluent of the WWTPs. Target compounds were extracted from wastewater and pre-concentrated using the optimized Oasis MAX solidphase extraction (SPE) method. During SPE, the pH of wastewater samples was adjusted to 2.5; then 100 mL of each sample was loaded onto a pre-conditioned cartridge. The SPE cartridge was rinsed with methanol: water (10: 90%, v: v) prior to sequential elution of retained analytes with 2 mL methanol, followed by 2 mL methanol and acetic acid (90: 10, v:v) and 2 mL of 2% (v:v) formic acid diluted using a mixture of methanol and acetic acid (40:60, v:v). The eluted analytes from the SPE cartridge were quantified using high performance liquid chromatography (HPLC) equipped with photo diode array detection. The analytical method was validated by spiking deionized water with 5 and 50 mu g . L-1 of target compounds, for which the recovery range of 76 to 98% was achieved with good precision. The instrument quantification limits obtained were 0.1 mu g . L-1, for naproxen and 0.4 mu g . L-1 for both ibuprofen and diclofenac. The detected concentrations for naproxen, ibuprofen and diclofenac in the influent of both WWTPs were in the ranges of 15-20 mu g . L-1, 55-69 mu g . L-1 and 6.4-16 mu g . L-1, respectively. In effluent, the detected concentrations for naproxen, ibuprofen and diclofenac were in the ranges of 0.6-1.1, 2.1-4.2 and 1.4-2.0 mu g . L-1, respectively. Overall, the employed SPE-HPLC method led to rapid pre-concentration of target compounds prior to their trace quantification in wastewater samples.