Various carotenoids were analyzed by ultra-high-pressure liquid chromatography with tandem mass spectrometry detection (UHPLC-MS/MS). Three different techniques to ionize the carotenoids were compared: electrospray ionization (ESI), atmospheric pressure chemical ionization (APCI) and atmospheric pressure photoionization (APPI). For all of the carotenoids tested, it was possible to obtain characteristic transitions for their unequivocal identification using each ionization technique. APCI was shown to be a more powerful technique to ionize the carotenoids than ESI or APPI. Transitions to differentiate carotenoids that coelute were determined to distinguish antheraxanthin from astaxanthin and lutein from zeaxanthin. In addition, four dopants were evaluated to improve ionization and enhance the carotenoid signal strength in APPI. These dopants were acetone, toluene, anisole, and chlorobenzene. Carotenoids improved their response in almost all cases when a dopant was used. The use of dopants allowed the enhancement of the carotenoid signals strength up to 178-fold.

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A specific, sensitive, precise, and accurate method for the determination of abscisic acid (ABA) in grapevine leaf tissues is described. The method employs high-performance liquid chromatography and electrospray ionization-mass spectrometry (LC-ESI-MS) in selected ion monitoring mode (SIM) to analyze ABA using a stable isotope-labeled ABA as an internal standard. Absolute recoveries ranged from 72% to 79% using methanol/water pH 5.5 (50:50 v/v) as an extraction solvent. The best efficiency was obtained when the chromatographic separation was carried out by using a porous graphitic carbon (PGC) column. The statistical evaluation of the method was satisfactory in the work range. A relative standard deviation (RDS) of < 5.5% and < 6.0% was obtained for intra-batch and inter-batch comparisons, respectively. As for accuracy, the relative error (%Er) was between -2.7 and 4.3%, and the relative recovery ranged from 95% to 107%.