Methyl retinoate chromatography

Baillet, A., Corbeau, L., Rafidson, R, and Ferrier, D., Separation of isomeric compounds by reversed-phase high-performance liquid chromatography using Ag+ complexation. Application to cis-trans fatty acid methyl esters and retinoic acid photoisomers, /. Chromatogr., 634, 251, 1993. 

Besler et al. [671] studied retinal and retinol isomer retention on a silica column (A = 325nm or 371 nm) with hexane/MlBE (97/3 and 93/7), hexane/dioxane (93/7 and 94/6), and heptane/MrBE (94/6 and 93/7) mobile phases. The purpose of this work was to find an accq)table replacement for dioxane, namely, MrBE. The best overall chromatography resulted when 94/6 hexane/dioxane resolved 11,13-di-cis-, 13-CIS-, 9,11-13-tri-cis-, 9,13-di-cis-, 11-cis-, 7,1 l-di-c , 9-cis-, 7,9-di-cis, and all-tra s retinol in 15 min. Broader peaks but better resolution were obtained for the same solute set when 93/7 hexane/MtBE was used (elution was complete in 21 min), MlBE in hexane also gave excellent resolution of 13-c/s-retinoic acid and z -trans retinoic acid methyl esters on a silica column (A = 340 nm) in <5 min, whereas dichloromethane/hexane (35/65) required 17 min and toluene/hexane (45/55) required 10 min. It was found that for the toluene/hexane mobile phase, very small changes in the water content of the system dramatically and adversely affected the chromatography. The MrBE/hexane mobile phase provided more overall stability with respect to these changes. 

Retinoic acid and other retinoid carboxylic acids, however, can be readily converted to derivatives that are suitable for gas chromatography. Many of these applications have used mass spectrometry for detection (see below). Diazomethane is used, at room temperature, to prepare the methyl esters without apparent isomerization. Pentafluorobenzyl esters of retinoic acid and its analogs have also been prepared for GC-MS (280) or HPLC-MS (281). Deuterated analogs of retinoic acid or other retinoid carboxylic acids have been used as internal standards, with mass spectrometric detection (88,282) (reviewed by Napoli [283] and by De Leenheer and Lambert [89]). The pentafluorobenzyl ester of a synthetic retinoid, Ro 13-7410, was analyzed by column switching the peak of interest from a SE54 colunm was cut to an OV 240 column, with subsequent detection by negative ion chemical ionization mass spectrometry (280). 

---