In high-performance liquid chromatography (HPLC), what does the term isocratic refer to?

Isocratic in high-performance liquid chromatography (HPLC) refers specifically to a condition where the mobile phase consists of a constant solvent composition throughout the analysis. This means that the mixture of solvents used in the mobile phase does not change during the run, leading to a stable elution environment.

Maintaining a constant solvent composition allows for reproducibility and consistency in the separation of the components within the sample. It helps in achieving optimized retention times for the analytes, which is crucial for accurate identification and quantification. Isocratic elution is especially effective for samples that have similar properties and where a fixed polarity solvent system can effectively separate the compounds.

In comparison, other factors such as temperature, stationary phase equilibration, or the flow rate can influence the separation process in different ways, but they do not define the term "isocratic." Therefore, the concept of having a constant composition of the mobile phase is central to understanding what isocratic refers to in the context of HPLC.