In LC/MS the trend is towards collecting as much data as possible – e.g. in drug metabolism or environmental screening.
The most accurate way is to use isotopically labelled standard substances. If these are commercially available, they are expensive.
- Available isotopically labelled standards are expensive.
- Standards are not available for most of the substances.
- Synthesising a standard in-house is time-consuming and tedious.
- Using structrally similar compounds leads to misleading results – using positional isotope may lead to a misestimation of concentration of 40 times.