There are several anti-ethylene chemicals. Silver thiosulfate (STS) is used on flowers. Aminoethoxyvinyl-glycine (AVG, trade name ReTain) blocks ethylene synthesis. It is applied preharvest. The fruit (plant) will not produce much ethylene, so there is not an ethylene response. The ethylene blocker 1-methylcyclopropene (1-MCP, trade name EthylBloc) blocks ethylene by binding to its receptor. It is applied postharvest. The fruit (plant) may still produce some ethylene, but there is no response to the ethylene.
There are several ways to measure ethylene: 1) gas chromatography (best but expensive); 2) kitagawa tubes, or equivalent; 3) other types of chemical sensors; or 4) another plant that is sensitive to ethylene.