[Skip to Content](https://www.sigmaaldrich.com#main-content) [![MilliporeSigma](https://www.sigmaaldrich.com/static/logos/purple/millipore_sigma.svg)](https://www.sigmaaldrich.com/US/en) Products Cart0 USEN Products ProductsApplicationsServicesResourcesSupport [Login / Register](https://www.sigmaaldrich.com/oidc-sign-in) [Order Lookup](https://www.sigmaaldrich.com/US/en/order-lookup) [Quick Order](https://www.sigmaaldrich.com/US/en/quick-order) Cart0 [Home](https://www.sigmaaldrich.com/US/en)[Small Molecule HPLC](https://www.sigmaaldrich.com/US/en/applications/analytical-chemistry/liquid-chromatography/small-molecule-hplc)Ascentis® Express U/HPLC Column Selection # Ascentis® Express U/HPLC Column Selection ## Column selection by phase chemistry The column selectivity has the highest influence on resolution in chromatography. Therefore, the selection of the best suitable column chemistry for the target analytes is an important selection parameter. C18 column chemistries are typically the first choice. Nevertheless, when a C18 doesn't give the desired separation or the sample contains compounds that are known to be difficult to retain or resolve on a C18, consider changing stationary phases. The range of selectivity provided by Ascentis® Express makes this easy. The flowchart below helps guide users in the selection of an Ascentis® Express phase, based on the particular compound type or separation challenge ![Ascentis® Express HPLC Column Selection Guide](https://www.sigmaaldrich.com/content/dam/cms-commons/sigmaaldrich/marketing/global/images/technical-documents/articles/analytical-chemistry/small-molecule-hplc/guide-to-selecting-ascentis-express-uhplc-hplc-column-phases.jpg "guide-to-selecting-ascentis-express-uhplc-hplc-column-phases") ## column selection by column dimension The separation goals, detection method and the instrument used for the separation define the column dimension and the particle size. ### Select Column ID NeedsColumn ID (mm)Typical Flow Rate (mL/min) Best Suitability for Mass Spec and UHPLC2.10.2 – 1.0 Solvent Savings in HPLC3.00.5 – 2.0 Standard HPLC4.61.0 – 3.0 ### Select Column Length NeedsColumn Length (mm) Maximize Speed20 - 75 Balance of Resolution and Speed100 Maximize Resolution150 ### Select Particle Size NeedsParticle Size (µm) UHPLC / High Throughput2.0 Fast on any HPLC System2.7 "Plug and Play" for Improving Existing HPLC Methods5.0 __Related Technical Articles__ - [Ascentis® Express Biphenyl UHPLC and HPLC Columns](https://www.sigmaaldrich.com/US/en/technical-documents/technical-article/analytical-chemistry/small-molecule-hplc/ascentis-express-biphenyl-uhplc-and-hplc-columns) - [Ascentis® Express C18 U/HPLC Columns](https://www.sigmaaldrich.com/US/en/technical-documents/technical-article/analytical-chemistry/small-molecule-hplc/ascentis-express-c18-u-hplc-columns) - [Ascentis® Express C8 U/HPLC Columns](https://www.sigmaaldrich.com/US/en/technical-documents/technical-article/analytical-chemistry/small-molecule-hplc/ascentis-express-c8-u-hplc-columns) - [Ascentis® Express F5 (Pentafluorophenyl) U/HPLC Columns](https://www.sigmaaldrich.com/US/en/technical-documents/technical-article/analytical-chemistry/small-molecule-hplc/ascentis-express-f5-pentafluorophenyl-u-hplc-columns) - [Ascentis ® Express HILIC U/HPLC Columns](https://www.sigmaaldrich.com/US/en/technical-documents/technical-article/analytical-chemistry/small-molecule-hplc/ascentis-express-hilic-u-hplc-columns) - [Ascentis® Express Phenyl Hexyl Columns for U/HPLC](https://www.sigmaaldrich.com/US/en/technical-documents/technical-article/analytical-chemistry/small-molecule-hplc/ascentis-express-phenyl-hexyl-columns) Top __Sign In To Continue__ To continue reading please sign in or create an account. 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