*2.6. Specific Selectivity and Spike Recovery for Cr6+ Detection in Tea*

According to the previous literature [23,24], common metal ion pollutants in tea include Hg2+, Mn2+, Ni2+, Pb2+, Cu2+, Cd2+, Fe3+, As3+, and Na+. To validate the selectivity of carbimazole in detecting Cr6+, the change of Raman intensity at the characteristic peak (595 cm−1) was compared when these metal ions were added to the system at an equal concentration (100 μg/L). Additionally, the experiment was repeated 3 times for the spiked tea sample (5 μg/L), and the spectra of 15 different points were obtained on each prepared detection solution to analyze the repeatability of the method. The relative standard deviation (RSD) of the spectral intensity at the characteristic peak was calculated to analyze the repeatability of the detection method. the reproducibility of the method

The quantitative data obtained from the SERS analysis were compared against the standard ICP-MS method [25]. Tea samples with different concentrations of Cr6+ (2.5, 5, 10, 20 mg/kg) were used for ICP-MS analysis with triplicates, and the recovery rate and RSD values were calculated for each sample. Thus, the practical applicability of the developed method for the detection of Cr6+ was confirmed.
