2.5.1. Antioxidant Activity—DPPH Assay

The antioxidant capacity of the aqueous extract of Ephedra aphylla and its selenium and zinc nanoparticles was investigated following the DPPH^• colorimetric method using ascorbic acid as a standard by way of the assay reported by Kitts et al. [39]. The serial dilution of each sample was prepared by mixing the sample with methanol in an equivalent amount. The DPPH^• solution was prepared in a concentration of 0.135 mM and mixed with each sample in the serial dilution with a volume of 1 mL. after the addition of DPPH^• solution; the samples were kept in the dark for 30 min at room temperature. The absorbance of each sample was measured at 517 nm in the next step. The % DPPH^• remaining was calculated using Equation (1):

The values of % DPPH^• remaining were plotted versus mg extract/mL using an exponential curve to identify the inhibitory concentration “IC₅₀”. IC₅₀ indicates the constitutes amount of antioxidants needed to decrease the initial concentration of DPPH^• solution by 50%. The values of IC₅₀ point out the inverse relationship with the antioxidant capacity of the tested sample [40].