The retention time together with the UV spectrum of individual peaks can be considered characteristic, and can easily be used to detect known coumarins in a crude extract. The coupling of MS to LC-PDA provides further structural information that is helpful for on-line identification of individual coumarins in any crude extract. AGI-6780? Various coumarins together with other oxygen heterocyclic compounds, e.g., psoralens and polymethoxylated flavones, present in the nonvolatile residue of the citrus essential oils of mandarin, sweet orange, bitter orange, bergamot, and grapefruit, were analyzed by atmospheric pressure ionization (API) LC-MS system equipped with an APCI probe in positive ion mode. Recording MS spectra at different voltages provided information on molecular weight as well as fragment ions, and this allowed the identification of the main components in the extracts.
In this study, cold-pressed citrus oils were analyzed by a Shimadzu LC system coupled with UV and MS detector with an APCI interface. The LC separation was carried out on a C18 Pinnacle column (250 �� 4.6 mm, 5 mm), eluted isocratically or using a gradient at a flow rate of 1 mL/min with the solvent mixture: solvent A (THF:ACN:MeOH: water?15:5:22:58) and solvent B (100% ACN). As coumarins are UV-absorbing compounds, they could be detected at 315 nm. The MS acquisition conditions were as follows: probe high voltage, 4 kV; APCI temperature, 400��C; nebulizing gas (N2) flow rate, 2.5 L/min; curved desolvation line (CDL) voltage, 25.5 V; CDL temperature, 230��C; deflector voltage, 25 and 60 V; and acquisition mode SCAN, 50�C500 m/z.
Carotenoids This group of natural products includes the hydrocarbons (carotenes) and their oxygenated derivatives (xanthophylls). LC-TLS has been applied successfully for the determination of carotenoids in four marine phytoplankton species, and a good degree of separation of diadinoxanthin, diatoxanthin, and other carotenoids has been achieved by isocratic HPLC elution with a greater sensitivity and selectivity than UV detection. This technique has allowed the monitoring of the interconversion of diadinoxanthin to diatoxanthin, and changes of other carotenoids under different light conditions. LC-TLS has also been found to be an ultrasensitive method for determination of b-carotene in fish oil-based supplementary drugs.
 Carfilzomib Essential oil and volatile components GC-MS has been demonstrated to be a valuable analytical tool for the analysis of mainly nonpolar components and volatile natural products, e.g., mono- and sesquiterpenes. Chen et al. described a method using direct vaporization GC-MS to determine approx 130 volatile constituents in several Chinese medicinal herbs. They reported an efficient GC-MS method with EI for the separation and structure determination of the constituents in ether-extracted volatile oils of Chinese crude drugs, Jilin Ginseng, Radix aucklandiae, and Citrus tangerina peels.