Determination of total chromium in tea samples by suspension dispersive solid phase extraction combined with silver nanoparticles and using flame atomic absorption spectrometry

Abstract

A method to separate and preconcentrate trace levels of chromium using silver nanoparticle (Ag NP) technology and suspension dispersive solid phase extraction is proposed. The synthesized Ag NPs combine with chromium to form aggregations. Suspension dispersive solid phase extraction is based on the reaction of zinc sulfate (ZnSO₄) and sodium hydroxide (NaOH) to form a zinc hydroxide suspension. The UV-vis absorption spectra and transmission electron microscopy (TEM) confirmed the aggregation of the Ag NPs. The influence of several parameters, such as volume of silver nitrate, extraction temperature, the solution pH, type and mass of the sorbent, vortex time, equilibration time, Ag NP volume, and the type, concentration and volume of the acid and foreign ions were investigated and optimized. Linearity was investigated from 10 to 1000 μg L⁻¹, and the correlation coefficient was 0.9988. Recoveries of 97.7–103.3% and an enrichment factor of 20 were achieved with 40 mL of sample. The LOD was 3.2 μg L⁻¹ for total chromium, and the relative standard deviation (RSD) was 4.2% at 20 μg L⁻¹. This method is simple and is successfully applied for the determination of chromium in tea samples with satisfactory results.