Which agent should NOT be contained in the leak detectant used to check the final connection of piping systems?

The agent that should not be contained in the leak detectant used to check the final connection of piping systems is ammonia. Ammonia is a hazardous substance that can pose significant health risks, including respiratory irritation and other toxic effects, especially in confined spaces. Its strong odor can also complicate leak detection, as it can easily mask or mislead the identification of other gases. Therefore, using ammonia as a leak detectant can create safety hazards for personnel and may not provide a reliable means of detecting leaks in medical gas systems.

On the other hand, the other substances listed, like chlorine, ethylene, and carbon dioxide, serve different roles in industrial applications and have specific safety protocols surrounding their use, albeit with precautions. However, ammonia's inherent risks and properties make it unsuitable for this particular purpose within medical gas systems.