Advantages of using a modified orthogonal sampling configuration originally designed for LC-ESI-MS to couple CE and MS for the determination of antioxidant phenolic compounds found in virgin olive oil.
A ThermoFinnigan sheath liquid flow capillary electrophoresis-mass spectrometry system designed for coupling via a co-axial interface was coupled through an adapted via an alternative, commercially available interface for orthogonal sampling. The affordable, reversible structural alterations made in the commercial LC-MS interface resulted in improved analytical performance. The results of a conventional capillary electrophoresis (CE) method using a commercial co-axial source to determine antioxidant phenolic acids present in virgin olive oil, were compared with those obtained by using a modified orthogonal sampling position. In both cases, separations were done using a 10 mM ammonium acetate/ammonium hydroxide buffer solution at pH 10.0 and a constant applied voltage of 25 kV. The operating variables for the mass spectrometry interface were re-optimized for the modified orthogonal orientation. This allowed the sheath liquid, sheath gas flow rates and capillary voltage to be lowered with respect to the co-axial coupling configuration. In addition, the orthogonal sampling position provided a higher selectivity by effect of ion sampling excluding larger droplets-with an increased momentum along the axis-which were drained through the sink at the bottom of the ion source. Also, the new configuration facilitated sample ionization, improved electrospray stability and led to stronger signals as a result. The new system was validated in terms of precision (repeatability), linearity, and limits of detection and quantification. A comparison of the validation data with the results previously obtained by using a commercial co-axial configuration revealed the adapted orthogonal sampling position to provide better repeatability in both migration times and relative peak areas (<1% and 7% respectively with n=15 replicates), a good linear range (with levels in the microgram-per-litre region) and lower limits of detection-especially for the compounds detected with the lowest sensitivity when co-axial ESI was used, as HFA, GEN, FER and VAN finding LOD among 24-3.0 microg L(-1) respectively.
Nevado
Juan José Berzas
JJ
Department of Analytical Chemistry and Food Technology, University of Castilla-La Mancha, Ciudad Real, Spain. juanjose.berzas@uclm.es
Peñalvo
Gregorio Castañeda
GC
Robledo
Virginia Rodríguez
VR
D000975:Antioxidants / Q000032:analysis* / Q000737:chemistry; D002853:Chromatography, Liquid; D019075:Electrophoresis, Capillary / Q000379:methods; D062385:Hydroxybenzoates / Q000032:analysis* / Q000737:chemistry; D057230:Limit of Detection; D015394:Molecular Structure; D000069463:Olive Oil; D010938:Plant Oils / Q000032:analysis / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods
D000975:Antioxidants; D062385:Hydroxybenzoates; D000069463:Olive Oil; D010938:Plant Oils; C017616:phenolic acid