Apparatus and method for introducing a sample into a separation unit of a chromatography system

An apparatus for introducing a sample into a separation unit of a chromatography system with a mobile phase, the mobile phase comprising a first mobile phase component and a second mobile phase component, the apparatus comprising:

• an injection unit;
• a first pump system configured to provide the first mobile phase component, a first portion of the first mobile phase component flowing from the first pump system through a first branch to the injection unit, and a second portion of the first mobile phase component flowing through a second branch;
• a second pump system configured to provide the second mobile phase component, at least a first portion of the second mobile phase component flowing from the second pump system through a third branch to the injection unit;
• and
• an input junction configured to provide a combined stream, comprising the first portion of the first mobile phase component provided via the first branch and the first portion of the second mobile phase component provided via the third branch, wherein:
• the injection unit is configured to receive the combined stream from the input junction and to inject the sample into the combined stream to form a sample-containing stream;
• and
• the sample-containing stream is subsequently combined with the second portion of the first mobile phase component provided via the second branch to form a diluted sample-containing stream, which flows to the separation unit of the chromatography system for separating sample constituents.