A green liquid phase microextraction using phthalic acid as switchable hydrophilicity solvent for the HPLC determination of sildenafil (Viagra®) in human urine.

[Display omitted] • Phthalic acid as switchable-hydrophilicity solvent for the extraction of sildenafil. • No sample cooling is required for the solidification of phthalic acid. • The analytical protocol is rapid using environmentally friendly solvents. Herein, a green liquid phase microextraction protocol using phthalic acid as switchable hydrophilicity solvent (SHS) is reported for the quantification of sildenafil in authentic human urine. The analyte was extracted onto phthalic acid solid particles which were produced through acidification of the sample. Its solidification was accomplished at ambient conditions without sample cooling. The determination of the sildenafil was carried out using high performance liquid chromatography-ultraviolet detection (HPLC-UV). The microextraction parameters that affect the extraction efficiency of the drug (i.e. SHS type and its concentration, acid type and concentration, extraction time, filter type) have been studied. The optimized analytical protocol involved the mixing of 300 μL of phthalate solution (0.75 M) with 600 μL of sample, followed by the addition of 50 μL of concentrated H 3 PO 4. The produced solid was collected using membrane syringe filter (0.45 μm) and was finally dissolved in 500 μL of CH 3 OH. Method validation data showed determination coefficient ≥ 0.99 for the linear range of 50 – 2000 ng/mL. The limit of detection (LOD) and the lower limit of quantitation (LLOQ) were 30 and 100 ng/mL, respectively. The accuracy (expressed as % recovery) of the method ranged between 88.0 – 108.9 % while the precision (expressed as % RSD) was less than 17.8 % in all cases. The robustness of the microextraction procedure and the instrumental method were investigated using Plackett-Burman experimental designs. The applicability of the method was demonstrated by analyzing both spiked and authentic human urine samples after oral administration of drug-containing pharmaceutical formulation. The developed protocol offers cost-efficiency, handling simplicity, and high throughput. Its green character was evaluated using Green Analytical Procedure Index and Blue Applicability Grade Index. [ABSTRACT FROM AUTHOR]