Application of a Novel Metal-Phase Microextraction as a Solventless Method for Determination of Nickel in Water Samples

In the present study, an environmentally friendly microextraction of nickel based on solid-phase method coupled to flame atomic absorption spectrophotometry was investigated. Due to elimination of organic solvents in this method, it can be used as a green technique to extract and reduce the detection limit of nickel in water samples.

By adding 0.06 g sodium borohydride (NaBH4) to 100 ml of the solution containing Fe (II) ions with concentration of 12 mg/l and nickel, these ions were converted to zero-valent particles. The nickel revived particles were trapped in the iron microparticles and deposited with them. After that, the solid phase produced was dissolved in 200 µl  of hydrochloric acid (HCl) 6N and the nickel concentration was measured using atomic absorption method. To optimize the process, effect (1 to 8), the amount of potassium hydrogen phthalate (KHP) (0.02-0.30), Fe (II) concentration (2.20-5.00 mg/l), NaBH4 (0.20-0.01 g), time (0.5-15.00 minutes), and temperature (20° -80°  C) were investigated. In addition, the effect of interfering ions was evaluated. Finally, the figures of merit were calculated, and the function of the method was investigated in the real water samples.

According to the performed optimization, pH = 4.5, NaBH4 = 0.06 g, Fe (II) = 2.5 mg/l, KHP = 0.08 g, time= 4 minutes, temperature = 50° C , and sample size = 100 ml were the optimum conditions. Besides, the concentration factor of 410, the detection limit of 0.3 ng/ml, and relative standard deviation (RSD) of 2.7% were obtained.

Due to the low detection limit and the elimination of organic solvents in nickel microextraction, this method can be a suitable method for determining trace amount of nickel with high efficiency. The low detection limit is due to the high concentration factor, which is significantly higher than the other microextraction methods.