Many factors affect selectivity in chromatography. In this seminar we discuss why selectivity should always be considered first in new method development activities and / or sample screening from both theoretical and practical viewpoints. For charged species, exploring mobile phase pH can be a powerful tool to influence selectivity and retention for: complex sample method development, peak shape optimisation, isolation work or to ensure all analytes are observed before final method lock down. Examples with practical tips for each of these scenarios are provided. A brief review of the effects of mobile phase pH on the analytes and the column / stationary phase is included. The buffer system choices across the pH range are also discussed with tips to ensure consistent reproducible chromatography. For a range of analytes various pragmatic UHPLC / HPLC method development platforms based on porous and solid core particles (compatible with broad mobile phase pH ranges from pH 1.5 – 11.0) are described. The column and mobile phase selections in these method development platforms are supported with various selectivity data and chromatography demonstrating orthogonality.