Studied a fair bit of chemistry, but not a pro, so this is only a rough outline.
A lot of chemical test equipment use semiconductor sensors of some kind - optical or otherwise - and most likely the sensitivity limit is simply the noise floor of the sensors. In good instruments they tend use good, or amazing detectors but they are still operating at the noise floor, or sometimes even below.
So running tests again doesn't really help sensitivity, for that you would most likely have to use some chemical process that amplifies the effect of the contaminants you are looking for. Hence the problem of having to know what to lool for in validating new chemicals, if you need ultra pure chemicals.
A lot of chemical test equipment use semiconductor sensors of some kind - optical or otherwise - and most likely the sensitivity limit is simply the noise floor of the sensors. In good instruments they tend use good, or amazing detectors but they are still operating at the noise floor, or sometimes even below.
So running tests again doesn't really help sensitivity, for that you would most likely have to use some chemical process that amplifies the effect of the contaminants you are looking for. Hence the problem of having to know what to lool for in validating new chemicals, if you need ultra pure chemicals.