Depends on the assay. Several mg for the assay

G. G. A. Balavoine and Yu. V. Geletii, Nitric Oxide 3, 40 (1999).

Depend of the assay, sample, triplicates...

Article The hydrophilic and lipophilic contribution to total antioxi...

Most antioxidant activity assays, especially microplate-based ones like DPPH or TAC, require as little as 10–20 µl of sample per well, making them suitable for limited sample amounts. Careful dilution and assay planning can help maximize data from minimal sample volumes.

The minimum sample size for assessing antioxidant activity depends on several factors, including the type of study, the variability of the data, and the statistical methods used. However, here are some general guidelines:

1. Pilot Studies: If your resources are limited, a pilot study with at least 5-10 samples can help estimate variability and inform future studies.

2. Statistical Power: Aim for at least 20-30 samples per group for more robust studies to achieve adequate statistical power (usually 80%).

3. Effect Size: Smaller sample sizes may be sufficient if you expect a large effect size. Conversely, more samples are needed if the effect size is small.

4. Replicates: Consider including technical replicates for each sample to increase reliability.

5. Statistical Tests: The choice of statistical tests can also influence sample size requirements; some tests are more robust to small sample sizes than others.

If you're working with a few samples, clearly state this limitation in your study and consider using appropriate statistical methods to account for it.