Cloud point-TiO2/sepiolite composites extraction for simultaneous preconcentration and determination of nickel in green tea and coconut water

In this work, cloud point-TiO2/sepiolite composites–octyl alcohol extraction combined with UV–vis spectrometry was applied to analyze nickel in real samples. Trace nickel was separated and preconcentrated with PAN as chelating agent, and TiO2/sepiolite composites—octylphenoxypolyethoxyethanol (TX-114)—octyl alcohol as extraction agent. Factors influencing extraction efficiency, such as concentrations of TX-114 and octanol, type of the desorption on the extraction system, concentration of chelating agent, pH, incubation temperature, incubation time and conditions of phase separation were investigated and optimized systematically. The results showed that TiO2/sepiolite composites exert significant effects on the extraction efficiency; especially nickel concentration is very low. Under the optimal conditions, the absorbance signal is linear with nickel concentration in the range of 0.02–3 mg L−1and the detection limit was 5 μg L−1. The developed method was successfully applied to the determination of nickel in natural products of Baisha green tea and coconut water in Hainan.