Theory of Chromatography

Introduction to Supercritical Fluid Chromatography

Substances can be in a solid, liquid, or gaseous state depending on the temperature and pressure conditions. For example, water is a liquid at room temperature and pressure, but at atmospheric pressure, it changes to vapor (gas) at 100 degrees C and ice (solid) at 0 degrees C. When water is placed inside a sealed container and subjected to a vacuum as shown in Fig. 1, some of the water evaporates and the remainder remains in a liquid phase. When the water vapor pressure reaches a certain value, the evaporation rate becomes equal to the condensation rate. This is referred to as the saturated water vapor pressure and depends on temperature.

As the vessel is heated, the liquid water expands and evaporates, so that its density is reduced. This leads to an increase in the density of the vapor phase. If the temperature exceeds 374 degrees C and the pressure exceeds 22.06 MPa, the density of the liquid and vapor phases becomes the same, making it impossible to distinguish between liquid water and water vapor. The water in this state will not become liquid even if the pressure is increased further. In other words, it’s like a dense gas that doesn’t liquefy.

Introduction to High-performance Liquid Chromatography

HPLC is an abbreviation for high-performance liquid chromatography. Chromatography refers to the measurement method, chromatogram refers to the measurement results, and chromatograph refers to the instrument. Chromatography separates components in a particular substance and performs qualitative and quantitative analyses on those components. Qualitative analysis refers to “what kind of compound each component is”, and quantitative analysis refers to “how much of each component is present”