Veterinary Drug Analysis: The Role of Isomers and Metabolites

In recent years, it is shown that the presence of isomers and
metabolites of veterinary drugs can affect the quantification and
identification of compounds present in a sample. If not handled with
care, results of a substance may be reported incorrectly, and
subsequent enforcement may be incorrect. WFSR has conducted a
study to investigate the analytical consequences of possibly present
isomers and metabolites on the analysis of the marker molecules. The
collected information was used to assess whether these compounds
could interfere in the official analysis, e.g., by yielding false-positive
or false-negative findings.
Here, two cases are presented that illustrate the analytical challenges
when it comes to isomers in official analyses. Each of these cases
poses different challenges and was chosen to demonstrate the
importance of being aware of the possible issues that can arise when
(un)knowingly dealing with isomers.