Careful selection of mobile phase composition, especially the buffer, is crucial for developing robust LC and LC-MS separations, optimizing selectivity, peak shape, and reproducibility. For samples with ionizable compounds, choosing the appropriate mobile phase pH to control the analyte's ionization state is essential for achieving reliable retention times. The most robust method is typically achieved when the pH is set well away from the analyte's pKa, ideally ±2 pH units. In LC-MS, volatile buffers (e.g., ammonium formate or acetate) must be used instead of non-volatile ones (like phosphate), which would precipitate in the detector. Buffer concentrations typically range from 5 to 50 mM, with 5 to 10 mM providing sufficient buffering capacity. During mobile phase preparation, the pH should never be adjusted or measured after the organic modifier is added. For gradient methods, it is highly recommended to include the buffer or additive at an equal concentration in both the A and B lines to prevent reproducibility issues and sloping baselines. Finally, using modern, high-purity 'type-B' silica columns, such as Avantor® ACE® columns, is advised for improved peak shape and reproducibility.

Accurate LC-MS/MS determination of Poly- and Perfluoroalkyl Substances (PFAS) is complicated by background PFAS contamination from the LC system components, which co-elutes with sample analytes and causes inaccurate quantification. The Avantor® ACE® PFAS Delay Column is a mandatory, simple solution. Installed before the injector, this highly retentive column retains the system PFAS contamination, forcing it to elute significantly later than the sample PFAS. This separation effectively eliminates interference, safeguarding the analytical data integrity.

Avantor ACE HTP-MS columns are designed to provide a cost-effective solution for high-throughput LC- MS analysis. They are developed to meet the requirements of bioanalytical and environmental laboratories that need to analyze on increasing number of samples daily. The column uses a low-dead volume, cartridge-style holder with replaceable 10 × 2.1 mm cartridges packed with high-efficiency 2um UHPLC silica particles, The cartridges are pressure rated to 1,000 bar and Individually QC tested. This design allows for short gradient and re-equilibration times, dramatically reducing LC-MS method cycle times and substantially increasing sample throughput compared to standard format columns. LC-MS/MS offers high specificity, allowing quantification of different analytes even with co-elution. Examples include the separation of perfluoroalkyl substances (PFAS) In less than 2.5 minutes, achieving full resolution for seven of the eight analytes. Additionally, the rapid LC-MS/MS analysis of immunosuppressant drugs (Tacrolimus, Sirolimus, Cyclosporin A) was successfully performed in less than 1 minute by maintaining the HTP-MS column at 80 ℃ to ensure good chromatographic performance.