Sample injector with metering device balancing pressure differences in an intermediate valve state

A method of injecting a sample liquid in a sample chromatography system, the method including:

• (a) isolating a sample loop of the liquid chromatography system from a high-pressure fluidic path of the liquid chromatography system, the high-pressure fluidic path communicating with a liquid chromatography column of the liquid chromatography system, wherein the sample loop comprises a variable volume portion for loading the sample liquid into the sample loop;
• (b) placing the sample liquid in the sample loop preparatory to injecting the sample liquid into the high-pressure fluidic path;
• (c) with the sample liquid placed in the sample loop and with the sample loop remaining isolated from the high-pressure fluidic path, performing a pressure compensation operation in which a volume of the variable volume portion is decreased to raise the pressure in the sample loop from essentially ambient pressure to the operating pressure of the liquid chromatography column;
• and
• (d) connecting the sample loop to the high-pressure fluidic path so that a pump pressure from a high-pressure pump is applied to the sample loop to cause the sample liquid in the sample loop to flow from the sample loop through a portion of the high-pressure fluidic path to the chromatography column.