In such a case, transformation mechanisms are identifiable from plots of 13 C/12 C versus 15 N/14 N parent compound data, reflecting different underlying carbon- and nitrogen-isotope effects. The approach requires a relatively high amount of substance for gas chromatography–isotope ratio mass spectrometry (GC-IRMS) or LC-IRMS analysis (100 ng to 1 μg), which, for instance, requires extraction of 10 liters of groundwater at pesticide concentrations of 100 ng/liter. For the special case of chiral pesticides, enantiomer analysis may substitute for isotopes in such analyses as a result of stereoselective reactions.