Capillary electrophoresis‐electrospray ionization‐mass spectrometry method to determine the phenolic fraction of extra‐virgin olive oil

Abstract We describe the first analytical method involving SPE and CZE coupled to ESI‐IT MS (CZE‐ESI‐MS) used to identify and characterize phenolic compounds in olive oil samples. The SPE, CZE and ESI‐MS parameters were optimized in order to maximize the number of phenolic compounds detected and the sensitivity of their determination. To this end we have devised a detailed method to find the best conditions for CE separation and the detection by MS of the phenolic compounds present in olive oil using a methanol–water extract of Picual extra‐virgin olive oil (VOO). Electrophoretic separation was carried out using an aqueous CE buffer system consisting of 60 mM NH 4 OAc at pH 9.5 with 5% of 2‐propanol, a sheath liquid containing 2‐propanol/water 60:40 v/v and 0.1% v/v triethylamine. This method offers to the analyst the chance to study important phenolic compounds such as phenolic alcohols (tyrosol (TY), hydroxytyrosol (HYTY) and 2‐(4‐hydroxyphenyl)ethyl acetate), lignans ((+)‐pinoresinol and (+)‐1‐acetoxypinoresinol), complex phenols (ligstroside aglycon (Lig Agl), oleuropein aglycon, their respective decarboxylated derivatives and several isomeric forms of these (dialdehydic form of oleuropein aglycon, dialdehydic form of ligstroside aglycon, dialdehydic form of decarboxymethyl elenolic acid linked to HYTY, dialdehydic form of decarboxymethyl elenolic acid linked to TY) and 10‐hydroxy‐oleuropein aglycon) and one other phenolic compound (elenolic acid) in extra‐VOO by using a simple SPE before CE‐ESI‐MS analysis.