Unmodified and rGO-modified Zn/Al layered double hydroxides; nanoadsorbents employed for the solid phase extraction/HPLC determination of naproxen

The applicability of two layered double hydroxide adsorbents, that is, Zn/Al LDH and the reduced graphene oxide-modified Zn/Al-rGO LDH for the solid phase extraction-preconcentration of naproxen followed by HPLC determination is evaluated and compared. The adsorbents are characterized by using XRD, FT-IR, FE-SEM, BET, and TEM techniques. The optimization of parameters affecting the extraction procedure included pH and sample solution volume, amount of the adsorbents, adsorbent/sample solution contact time, type, concentration, and volume of the desorption solution, and the time required for desorption process was performed by using univariate method. It is assumed that the uptake of anionic form of naproxen is taken place via the ion exchange mechanism with interlayer carbonate anions of the studied LDHs. The applicability of the adsorbents is evaluated by the determination of naproxen in human urine, hospital, and pharmaceutical wastewater samples. The obtained linear ranges by employing the unmodified and modified LDHs for the determination of naproxen in pharmaceutical wastewater were found to be 10–530 µg L⁻¹ (R² = 0.9999) and 5–630 µg L⁻¹ (R² = 0.9999), respectively. The limits of detection and enrichment factor were appraised as 5.1 µg L⁻¹ and 42 by employing Zn/Al LDH, and 3.1 µg L⁻¹ and 54.5 by using Zn/Al-rGO LDH. Both investigated LDHs are able to be used in solid phase extraction-preconcentration of naproxen in real samples. However, the evaluated figures of merit reveal that the modified Zn/Al-rGO LDH is more efficient adsorbent than the unmodified Zn/Al LDH for the extraction of naproxen.