MS/MS was so well received because it provided the analyst with
a previously unknown degree of selectivity and sensitivity. Hence,
complex, labor-intensive, sample-processing techniques could be
significantly simplified. Analysts soon considered it normal that their
instrument only saw the things that it was told to see. However,
they also realized that monitoring a few known compounds does
not provide a comprehensive description of the sample as a whole.
For example, there was the need to monitor toxic metabolites of a
particular drug. The abuse of certain veterinary drugs could not be
proved by monitoring the short-living active drugs, but rather by
detecting metabolites that showed much longer clearance times.
In addition, the number of pesticides used had increased significantly,
so classic targeted analysis became more and more
challenging.