How to detect harmful gas occurence in carboy bottle To fill with drinkable water, I have lots of empty 19lt carboy bottles. Since they came from different people and companies, I have to check their healthiness to decide wheter they can be sterilise for reuse or not.

I need to detect if a 19lt carboy bottle was used previously for gas, lpg, diesel etc. or is there any other harmful chemical (such as urine) in it.

What could be the cheapest and trustable solution for it? Could I use gas sensors or infrared imaging or something else?

Thanks in advance.
Gas sensors are probably too specific. Infrared imaging is going to have to take account of the carboy material itself. However, sampling the air and performing a gc/ms analysis could work - basically its headspace analysis.