Fast and green separation of malachite green in water samples by micro-dispersion scanometry method without heating, cooling and organic solvents at room temperature

•Very trace level of Ni(OH)2 nanopowder is able to remove malachite green effectively.•Dispersive method can be done at room temperature without cooling and heating processes by salting out.•Sacanometry is a good alternative for UV–vis detector in dispersive method.•In micro level of reagents including non-ionic surfactant, no need to organic solvents to resolve surfactant rich phase. In the present work, novel, easy, rapid, green, and, economical technique, micro-dispersion scanometry (MDS) is presented for the first time and employed using suspended Ni(OH)2 nanopowder in the micellar medium for the determination of slight amounts of malachite green chloride. In the meanwhile, we introduced a new simple method for the synthesis of Ni(OH)2 nanopowder followed by characterization via various methods such as scanning electron microscopy (SEM), X-ray diffraction (XRD) and, Brunauer, Emmett and Teller (BET). The process of scanning (detecting) was done on the cells including the sample solution via a usual flatbed-scanner. Then, for analyzing the color of the cells, a software system designed in Visual Basic (VB 6), to R (red), G (green), and B (blue) values was applied. To build the cells, some holes were created in the plexiglas sheet. The impact of experimental variables namely pH, weight of sorbent, volume of 4% Triton X-114, eluting solution, and sample volume have been investigated and optimized in multivariate method using design Expert 7.0 software for statistical data analysis. A contrast done between the proposed and traditional UV–vis spectrophotometry methods revealed the comparable tendency in both methods Calibration curves were linear in the range of 0.37–110 and 0.45–110μgL−1 for scanometry and UV–vis methods, respectively. The detection limits were 0.060 and 0.068μgL−1 for scanometry and UV–vis methods, respectively. The capacity of Ni(OH)2 nanopowder for malachite green was 80mgg−1.