Determination of carotenoids by liquid chromatography/mass spectrometry: effect of several dopants

Abstract

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.

We thank Dr. C. Zhu and G. Farré (Departament de Producció Vegetal i Ciència Forestal (PVCF), Universitat de Lleida, Lleida, Spain) for supplying the transgenic maize seeds; Dr. P. Christou (PVCF and Institucio Catalana de Recerca i Estudis Avancats, Barcelona, Spain) for critical comments on the manuscript and the Comissionat per a Universitats i Recerca del DIUE de la Generalitat de Catalunya (Barcelona, Spain) and to the European Social Fund (ESF) for the PhD fellowship of Sol M. Rivera. This work was supported by the University of Lleida, Ministry of Science and Innovation (MICINN), Spain (BFU200761413 and CTQ2009- 14699-C02-01) and an ERC Advanced Grant (BIOFORCE) to Paul Christou