Ultrasound-assisted hollow fiber/ionic liquid-based liquid phase microextraction using an ionic liquid solvent for preconcentration of cobalt and nickel ions in urine samples prior to FAAS determination
Ultrasound-assisted (UA) hollow fiber (HF) liquid-phase microextraction (LPME) coupled with flame atomic absorption spectrometry (FAAS) has been developed to preconcentrate and determine ultra-trace amounts of cobalt (Co) and nickel (Ni) ions in human urine. To the best of our knowledge, no previous reports have described the coupling of UA-ionic liquid (IL)-HF-LPME with an FAAS system to analyze metal ions in biological samples. In this study, the ILs 1-hexyl-3-methylimidazolium hexafluorophosphate, sodium hexafluorophosphate, and 1-(2-pyridylazo)-2-naphthol were used as extraction, ion-pairing, and chelating agents, respectively. With the assistance of an ultrasonic probe, the analyte exchange between the phases increased, and the extraction efficiency of Co and Ni ions improved significantly. The collected extraction phase was subsequently analyzed directly through FAAS. Under optimized conditions, the detection limits of Co and Ni ions were 0.09 and 0.03 μg L−1, respectively. The precision of the analysis of Co and Ni ions was within a relative standard deviation of 10% under normal operating conditions. The ultrasonic assistance provided enrichment factors of 66 and 82 for Co and Ni ions, respectively. The recoveries of Co and Ni ions spiked in urine samples ranged from 93.8 to 104.3%. The practicality of the proposed method was demonstrated through satisfactory analyses of samples of a standard reference material and real human urine.