Determination of α‐tocopherol in infant foods by liquid chromatography combined with atmospheric pressure chemical ionisation mass spectrometry

Abstract

A novel, sensitive and specific method for the quantification of alpha-tocopherol in two infant foods (milk and cereals) using liquid chromatography on-line with positive atmospheric pressure chemical ionisation mass spectrometry detection (LC/APCI-MS) has been developed. The samples were first saponified in order to eliminate fats and to transform tocopherol esters into free tocopherol, followed up by a liquid-liquid extraction of the analyte in petroleum benzine/diisopropyl ether (75:25, v/v) prior to injection onto the LC system. For the quantification, deuterium-labelled tocopherol was used as internal standard and the samples were monitored in selected ion monitoring (SIM) mode. Calibration curves between 1-40 microg/mL of alpha-tocopherol showed a good linear correlation (r(2) = 0.99994), and the detection limit was determined to be 2.5 ng/mL. The within-day and between-day precision were determined for several dietetic infant formulae and certified reference samples, and found to be below 3.5%. The accuracy determined on a Nestlé reference sample (milk powder) was calculated to be 115.2 +/- 1.2%, which confirms the robustness of the proposed method. This study shows that single quadrupole LC/MS can be applied for the quantification of vitamins in food and the method offers better sensitivity and selectivity than traditional method such as LC-UV. This would simplify the preparation of the food samples and consequently enhance the vitamin analysis throughput in the food area.

Development of a liquid chromatographic time‐of‐flight mass spectrometric method for the determination of unlabelled and deuterium‐labelled α‐tocopherol in blood components

“…In this case the closest match corresponds to C 29 H 49 O 2 , which is the formula for α ‐tocopherol. The clear and monoisotopically resolved spectrum obtained by ESI‐TOF contrasts with the spectrum obtained in previous methods employing either single14 or triple12,13 quadrupole mass spectrometers. In these methods, APCI+ MS/MS,12 APCI+ MS,14 and ES+ MS/MS13 produced a cluster of ions for α ‐tocopherol in the m/z range 423–432, the expected target protonated ion not being the predominant species.…”

“…The clear and monoisotopically resolved spectrum obtained by ESI‐TOF contrasts with the spectrum obtained in previous methods employing either single14 or triple12,13 quadrupole mass spectrometers. In these methods, APCI+ MS/MS,12 APCI+ MS,14 and ES+ MS/MS13 produced a cluster of ions for α ‐tocopherol in the m/z range 423–432, the expected target protonated ion not being the predominant species. The presence of these additional ions has been attributed both to the oxidation of α ‐tocopherol, and to the protonation followed by dehydrogenation of α ‐tocopherol, during ionisation12 and represents novel ionisation characteristics.…”

“…However, the disadvantage of GC/MS is the need for sample clean‐up and prior derivatisation of the samples which can greatly increase experimental error, especially as the trimethylsilyl derivatives are unstable and rapidly hydrolyse in the presence of moisture. Recently, a number of LC/MS methods for the analysis of tocopherols have been established 12–14. These methods involve either single14 or triple quadrupole12,13 instruments.…”

“…Recently, a number of LC/MS methods for the analysis of tocopherols have been established 12–14. These methods involve either single14 or triple quadrupole12,13 instruments. Until now, no time‐of‐flight mass spectrometry (TOFMS) methods for vitamin E analysis, or indeed analysis of biomolecules, have been available.…”

Products of the reaction between α- or γ-tocopherol and nitrogen oxides analyzed by high-performance liquid chromatography with UV-visible and atmospheric pressure chemical ionization mass spectrometric detection

“…Thus, other detection methods were investigated, and it was found that the application of atmospheric pressure chemical ionization (APCI)-MS to the usual HPLC afforded a partial improvement to the problem [32]. Furthermore, the use of a shorter column (150 mm × 4.6 mm i.d.)…”