Well, I was assuming this is a beginners chemistry question, so I thought I'd start out simple.
Have you used household strength hydrogen peroxide for any reason? Do you know what it does when used, and why? Can you tell us some more about your particular problem -- the peroxide poisoning of a patient? Class assignment? Mystery novel writing? Genuine criminal investigation with other facts available?
Ah, just checked your previous posts. Okay, H2O2 rapidly decomposes with a number of catalysts. I suppose chemically, NaI or Manganese dioxide are common ones, you can Google those. Another common catalyst is the enzyme catalase -- virtually all living things produce it, and it can be purchased in purified form. Large amounts of H2O2 rapidly fizz on contact with catalase, but trace amounts, I'm not so sure. Peroxide is a powerful oxidizing agent, but finding a red-ox titration (I know you tend to favor those) that is specific for just peroxide may be difficult. As for other tell-tale traces, peroxide breaks down to water and oxygen, and they're ubiquitous.