Preconcentration of fluid samples with alternating dual loop introduction

A sample preconcentration system comprising:

• a first sample loop and a second sample loop alternately fluidically coupled with a sample source;
• a first valve fluidically coupled with the first sample loop and the second sample loop and configured to alternately introduce fluid from the sample source to the first sample loop and the second sample loop;
• a second valve fluidically coupled with the first valve to alternately receive fluid from the first sample loop and the second sample loop, the second valve configured to be fluidically coupled with a preconcentration column and to alternately provide access to the preconcentration column to fluid received from the first sample loop and the second sample loop;
• and
• a pump system configured to alternately introduce sample held in the first sample loop and sample held in the second sample loop to the preconcentration column via the first valve and the second valve and to alternately introduce sample from the sample source into the first sample loop and the second sample loop.