SILVER-PLATED VITAMINS - A METHOD OF DETECTING TOCOPHEROLS AND CAROTENOIDS IN LC ESI-MS COUPLING/

In LC/MS, nonpolar substances in the majority of cases cannot be ioniz ed by standard electrospray ionization (ESI) because they obviously la ck a site for protonation or deprotonation. The ionization of caroteno ids and tocopherols can be greatly enhanced by the addition of sih er ions. The Ag+-carotenoid and Ag+-tocopherol adducts thus formed render these substances amenable to MS. alpha-, beta-, gamma-, and delta-toc opherol, alpha-tocopherol acetate, and the various isomers of lycopene and beta-carotene were separated by C-30 RP-HPLC and could be identif ied by online ESI-MS. A mixture of six different carotenoids was analy zed by scanning the mass range from m/z 500 to 800. The mass spectra o f the peaks revealed that all carotenoids and most tocopherols were pa rtially oxidized to radical cations,The detection limit for canthaxant hin was similar to 500 fmol while that of beta-carotene was below 300 fmol. An increase in sensitivity in the MRM mode can be attained by mo nitoring ions formed by loss of elemental silver from the adducts in t he CID cell. Dichloromethane extracts of tomato, carrot, and vegetable juices, a vitamin drink, and a commercial infant food product were an alyzed by LC/MS. After postcolumn argentation, from the mass-selective extracts of the TIC, the carotenoids and tocopherols present could be identified by their masses and their retention times. For all studies , a sih er perchlorate solution with an overall concentration of 50 mu g/mL was used.