Separation and photostability analysis of retinoic acid isomers and their derivatives based on ion mobility mass spectrometry and theoretical calculations.

Retinoic acid (RA) regulates cell proliferation, differentiation, and apoptosis and exists in three primary isomers: all-trans-RA (ATRA), 9-cis-RA (9cRA), and 13-cis-RA (13cRA). RA derivatives, such as bexarotene (BT) and arotinoid acid (TTNPB), are used to treat cutaneous T-cell lymphoma and induce cellular pluripotency. Due to their distinct biological activities, accurate identification and analysis of these isomers are crucial. This study developed a rapid and efficient method for analyzing RA isomers and their derivatives using ion mobility mass spectrometry (IM-MS) and theoretical calculations. RA isomers and derivatives exhibit overlapping mobilities and cannot be separated by direct IM-MS. By forming ternary complexes with β-cyclodextrin (β-CD) and metal ions, baseline separation was achieved with a peak resolution (R) of up to 3.42. Tandem MS and theoretical calculations revealed distinct differences in interactions, spatial structures, and binding energies, enabling mobility-based separation. Photostability tests showed rapid photoisomerization of 13cRA into 9cRA and ATRA within seconds. Analysis of 13cRA soft capsules from four brands demonstrated good stability, with measured content aligning closely with labeled values. This method offers a new approach for accurate RA isomer analysis, with potential applications in pharmaceuticals and food industries.