Partial loop injection is a well known way of sample introduction to HPLC. In ion chromatography, it is not yet used to a large extent. Liquid handling with Metrohm's Dosino technology now enables to use partial loop injection on a highly reproducible and accurate level. It includes multi-level calibration out of one standard solution. This Application Note shows its use for parallel anion and cation determination in tap water applying one single Sample Processor. The anion results are shown in Application Note S–287.