The aqueous component of the mobile phase might contain acids like formic, phosphoric or trifluoroacetic acid or salts to enable the separation of the sample components. The composition of the mobile phase is either maintained as a constant or as varied during the chromatographic analysis. The constant approach is effective for the separation of the sample components that are not very dissimilar in their affinity for the stationary phase. In the varied approach, the composition of the mobile phase differs from low to high eluting strength. The eluting strength of the mobile phase is reflected by analyte retention times where high eluting strength produces fast elution.