A dispersive liquid-phase microextraction method combined with UV–vis spectrophotometry was utilized to highly selective determination of creatinine in human serum and urine samples. To overcome the interferences in complex matrices, creatinine reacted with 1,4-naphthoquinone-2- potassium sulfonate reagent to produce a red coloured product that could be extracted into a small volume of 1-hexyl-3-methylimidazolium hexafluorophosphate ([HMIM]PF6) ionic liquid solvent. To increase the sensitivity of the assay, gluconic acid capped silver nanoparticles (Ag NPs) were used. On addition of Ag NPs to the red coloured extracted product, the solution turned to blue accompanied with a red shift in wavelength around 620 nm that could be detected by the naked eye. The effective variables on the determination of creatinine such as concentration of the reagent, amount of formic and hydrochloric acids, type and volume of the extractant, and concentration of Ag NPs were investigated. Under the optimal conditions, the calibration plot was bimodal with linear ranges from 0.1 to 1.5 µg mL−1 and 1.5 to 105 µg mL−1 creatinine with a limit of detection 0.1 µg mL−1. The relative standard deviation for five measurements at 35 µg mL−1 concentration level was 3.8%. The newly developed assay was used for the determination of creatinine in human serum and urine specimens with satisfactory results.
Determination of Total Hydroxyproline and Proline in Human Serum and Urine by HPLC with Fluorescence Detection.