After the pump, the mobile phase encounters the autosampler. An autosampler works by aspirating and injecting a precise sample volume into the mobile phase stream. Using an autosampler reduces manual labor and improves injection precision and accuracy compared to manual sample injection, an absolute priority for a quantitative HPLC analysis.
Types of autosamplers
All autosamplers aspirate a sample from a vial or well plate. Differences arise in sample placement inside the sample loop and the relationship of the needle to the mobile phase flow path. There are two main autosampler operating principles: pushed/pulled-loop and split-loop.
In pushed-loop and pulled-loop autosamplers, the sample is delivered into the sample loop either by pushing (pushed-loop) or aspirating (pulled-loop) with a syringe. Only the sample loop switches into the pump flow path for the separation during the actual injection process. In contrast, with the split-loop design, the needle is part of the sample loop, and no excess sample is required to fill the loop.
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