Instant Notes: Analytical Chemistry

● variations in the distribution ratio of a solute with its total concentration also

leads to asymmetricalor skewedpeaks (vide infra).

Figure 1 illustrates the symmetrical nature of a chromatographic peak and

symmetrical broadening. Figure 2 illustrates the mutiple-path, longitudinal

diffusion and mass transfer effects.

D2 – Principles of chromatography 125

Mobile phase

Stationary phase

Flow

Interface

Equilibrium concentration

Actual concentration

Fig. 1. The symmetrical nature and broadening of a chromatographic peak.

(a) Stationary phase particles

Mobile phase

SP

(b)

Mobile phase

Concentration

profile of band Forward and backward

diffusion in mobile phase

as band moves along

Analyte band

(c) Mobile phase

Movement onto SP

Stationary Analyte attracted onto SP

phase (SP)

Movement off SP

Fig. 2. Illustration of the three principal causes of band broadening: (a) multiple-path effect; (b) longitudinal diffusion
effect; (c) mass-transfer (non-equilibrium) effect. Reproduced from A. Braithwaite & F.J. Smith, Chromatographic
Methods, 5th edn, 1996, first published by Blackie Academic & Professional.