Isotope effect may cause partial
chromatographic separation of
labeled (heavy) and unlabeled (light) isotopologue pairs. Together
with a simultaneous matrix effect, this could lead to unacceptable
accuracy in quantitative liquid chromatography–mass spectrometry
assays, especially when electrospray ionization is used. Four biologically
relevant reactive aldehydes (acrolein, malondialdehyde, 4-hydroxy-2-nonenal,
and 4-oxo-2-nonenal) were derivatized with light or heavy (d3-, 13C6-, 15N2-, or 15N4-labeled) 2,4-dinitrophenylhydrazine
and used as model compounds to evaluate chromatographic isotope effects.
For comprehensive assessment of retention time differences between
light/heavy pairs under various gradient reversed-phase liquid chromatography
conditions, major chromatographic parameters (stationary phase, mobile
phase pH, temperature, organic solvent, and gradient slope) and different
isotope labelings were addressed by multiple-factor screening using
experimental designs that included both asymmetrical (Addelman) and
Plackett–Burman schemes followed by statistical evaluations.
Results confirmed that the most effective approach to avoid chromatographic
isotope effect is the use of 15N or 13C labeling
instead of deuterium labeling, while chromatographic parameters had
no general influence. Comparison of the alternate isotope-coded derivatization
assay (AIDA) using deuterium versus 15N labeling gave unacceptable
differences (>15%) upon quantifying some of the model aldehydes
from
biological matrixes. On the basis of our results, we recommend the
modification of the AIDA protocol by replacing d3-2,4-dinitrophenylhydrazine with 15N- or 13C-labeled derivatizing reagent to avoid possible unfavorable consequences
of chromatographic isotope effects.