Stop-flow comprehensive two-dimensional liquid chromatography combined with mass spectrometric detection for phospholipid analysis

Quantitative metabolite profiling utilizing parallel column analysis for simultaneous reversed-phase and hydrophilic interaction liquid chromatography separations combined with tandem mass spectrometry

In this work, a fully automated parallel LC column method was established in order to perform orthogonal hydrophilic interaction chromatography (HILIC) and reversed-phase (RPLC) chromatography within one analytical run for targeted quantitative mass spectrometric determination of metabolites from central carbon metabolism. In this way, the analytical throughput could be significantly improved compared to previously established dual separation work flows involving two separate analytical runs. Two sample aliquots were simultaneously injected onto a dual column setup columns using a ten-port valve, and parallel separations were carried out. Sub 2 μm particle size stationary phases were employed for both separation methods. HILIC and RPLC eluents were combined post column followed by ESI-MS/MS detection. The orthogonal separations were optimized, aiming at an overall separation with 2 retention time segments, while reversed-phase separation was accomplished within 5.5 min; metabolites on the HILIC phase were retained for a minimum time of 6 min. The overall run time was 15 min. The setup was applied to the quantification of 30 primary intercellular metabolites, including amino acids, organic acids, and nucleotides employing internal standardization by a fully (13)C-labeled yeast extract. The comparison with HILIC-MS/MS and RPLC-MS/MS in separate analytical runs revealed that an excellent analytical performance was achieved by the parallel LC column method. The experimental repeatability (N = 5) was on average <5% (only for 2 compounds >5%). Moreover, limits of detection for the new approach ranging from 0.002-15 μM were in a good agreement with ones obtained in separate HILIC-MS/MS and RPLC-MS/MS runs (ranging from 0.01-44 μM).

Determination of flavor enhancers in milk powder by one-step sample preparation and two-dimensional liquid chromatography

Maltol, ethyl maltol, vanillin, and ethyl vanillin are important food additives as flavor enhancers. To quantify the four additives in milk powder, a novel 2D liquid chromatographic (2DLC) method was developed in this article. In such a 2DLC system, the target fractions eluted from the first dimensional column (C4) are stored onto the trapping column (C8) for subsequent analysis; after that, they were switched into the second dimensional column (C18) by a two-position six-port switching valve. A one-step sample preparation method was used prior to 2DLC chromatographic analysis, which was easy and convenient. After optimization of all experimental parameters, the new method was validated in terms of linearity, LODs, and LOQs, intra- and interday precision, and accuracy. A conventional single-dimensional liquid chromatographic method was also proposed in this work for comparison. In order to evaluate the applicability of the new 2DLC method, five brands of commercial milk powder samples (n = 8) were analyzed. Vanillin and ethyl vanillin were detected in two samples, respectively. It is showed that the 2DLC method is effective in quality control programs of milk powder products.