Development of a micro-solid phase extraction procedure using a histidine-copper adsorbent for the extraction of Zn(II) and Cd(II) ions from tea samples.

In this study, a micro-solid phase extraction method was developed using a sorbent synthesized from histidine and copper nitrate for the extraction of Zn(II) and Cd(II) ions from tea samples. The extraction system consisted of a syringe cylinder with a compressed cotton layer as a filter, onto which a few milligrams of the sorbent were layered. The extract of the tea sample was passed through the sorbent and elution was performed using methanol. The extracted analytes were quantified by flame atomic absorption spectrometry. The effect of critical parameters such as sorbent amount, pH, eluate type and volume, salt, and flow rate on extraction efficiency was studied and optimized. Under optimal conditions, the method demonstrated linear ranges of 2-100 and 1-100 μg Kg^-1 with detection limits of 0.7 and 0.4 μg Kg^-1 for Cd(II) and Zn(II) ions, respectively. The intra- and inter-day relative standard deviations were ≤5% for repeated measurements, indicating good repeatability. This method was efficient without requiring vortexing or centrifuging steps, simplifying the procedure. Finally, by determining the concentrations of Zn(II) and Cd(II) ions in tea samples, the feasibility of the method was confirmed with relative recoveries between 94.5 and 100.8%.