Instantaneous potential, liquid phase chemical

Modern LC/MS systems employ two ionization processes that are accomplished at atmospheric pressure, termed electrospray (ESI) and atmospheric pressure chemical ionization (APCI). In a typical ESI source, the eluent from the HPLC column composed of liquid mobile phase and analyte molecules passes through a stainless steel capillary with a high positive or negative potential applied to the end (3-5 The electric-field causes instantaneous... [Pg.1703]

For any form of (gas or liquid) chromatography, one can define the distribution of solute between the stationary and mobile phases by an equilibrium (2). At equilibrium the chemical potentials of each solute component in the two phases must be equal. The driving force for solute migration from one phase to the other is the instantaneous concentration gradient between the two phases. Despite the movement of the mobile phase in the system, the equilibrium exists because the solute diffusion into and out of the stationary phase is fast compared with the flow rate. Under dilute solution conditions, the equilibrium constant (the ratio of solute concentrations in the stationary to the mobile phases) can be related to the standard Gibbs free-energy difference between the phases at constant temperature and pressure ... [Pg.2]