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

Abstract: Introduction: A simple alternative removal of iron and copper before the
determination of nickel 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 to KSCN before passing through
polyurethane foam (PUF) (1 cm i.d. × 8 cm length). Some metal ions-SCN complexes (e.g.,
Fe(III) and Cu(II)) were retained in the column while Ni(II) ions were kept 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.