Micro-Milli Scale for the Removal of Iron and Copper by a Positively Charged Foam before Nickel Colorimetric Detection using Handy Spectrometer

Abstract

Introduction: Simple alternative detection of nickel with iron and copper as interferences was proposed. The procedure was based on sampling a milligram sample and a micro-milliliter operation. Methods: The method has been applied to jewelry items. A 50 mg sample was digested by 5 mL of nitric acid with heating. The obtained solution was added with KSCN before passing through polyurethane foam (PUF) (1 cm i.d. × 8 cm length). Some metal ions-SCN complexed (e.g., Fe(III) and Cu(II)) were retained in the column while Ni(II) ions were in the eluate. A 200-500 µL aliquot was added with 4-(2-pyridylazo)-resorcinol (PAR) as the color reagent. At least 30 µL of a portion was measured for the absorbance of the color product using a handy spectrometer. Results: The positively charged foam could remove iron and copper altogether before determining nickel. A standard calibration was a plot of absorbance versus Ni(II) concentration for 1-30 mg/L: absorbance = 0.0123[Ni(II), mg/L] + 0.0435 (R2=0.9945) with a limit of detection (LOD) and limit of quantitation (LOQ) of 0.24 mg/L and 0.81 mg/L, respectively. Two bracelet samples showed the presence of nickel at 0.97 ± 0.25 and 0.27 ± 0.04 mg/g, respectively, and agreed with the reference FlameAAS method. Conclusion: The proposed method could be used to assay nickel in samples containing high levels of iron and copper, such as jewelry. This will benefit general wearers with health concerns associated with nickel, particularly in case of inexpensive accessories. The handy spectrometer used in the study might make be helpful to carry out these studies with a limited tight budget.